Ubiquitination in plant immunity

Available online at www.sciencedirect.com

Ubiquitination in plant immunityMarco Trujillo1 and Ken Shirasu2

Plant immune responses require the coordination of a myriad of

processes that are triggered upon perception of invading

pathogens. Ubiquitin, the ubiquitination system (UBS) and the

26S proteasome are key for the regulation of processes such as

the oxidative burst, hormone signaling, gene induction, and

programmed cell death. E3 ligases, the specificity

determinants of ubiquitination, have received by far the most

attention. Several single-unit ligases, which are rapidly induced

by biotic cues, function as both positive and negative

regulators of immune responses, whereas multisubunit ligases

are mainly involved in hormone signaling. An increasing body of

evidence emphasizes the heavy targeting of the UBS by

pathogen virulence effectors, underlining its importance in

immunity.

Addresses1 Julius-von-Sachs Institute, Department of Pharmaceutical Biology,

University of Wurzburg, Julius-von-Sachs Platz 2, Wurzburg, Germany2 Plant Immunity Research Group, RIKEN Plant Science Center, 1-7-22

Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan

Corresponding authors: Trujillo, Marco ([email protected]

wuerzburg.de) and Shirasu, Ken ([email protected])

Current Opinion in Plant Biology 2010, 13:402–408

This review comes from a themed issue on

Biotic interactions

Edited by Jane E. Parker and Jeffrey G. Ellis

Available online 12th May 2010

1369-5266/$ – see front matter

# 2010 Elsevier Ltd. All rights reserved.

DOI 10.1016/j.pbi.2010.04.002

IntroductionFrom perception to response, plants are in a race against

pathogens to react as quickly and effectively as possible.

It starts with the perception of conserved pathogen-

associated molecular patterns (PAMPs) mediated by

plasma membrane-located pattern recognition receptors

(PRRs), which relay the signal via mitogen activated

protein kinase (MAPK) cascades, leading to the activation

of immune responses known as PAMP-triggered immu-

nity (PTI). However, PTI can be suppressed by

pathogen-derived virulence effector proteins. In turn,

some effector proteins can be perceived by a different

subset of receptors that activates a second layer of

defense, called effector-triggered immunity (ETI) [1].

Launching of defense responses for these two branches of

immunity in plants requires ubiquitination for positive

and negative regulation. In addition, profound changes in


hormone levels take place that integrate biotic stress cues,

and recent studies have demonstrated the extent to which

ubiquitin-mediated proteolysis is involved in the regula-

tion of hormone signaling [2,3�].

Ubiquitin is a small (8.5 kDa) and highly conserved

protein modifier, tightly engaged in a wide range of

cellular processes [3�]. Modification of target proteins

by the covalent attachment of ubiquitin, termed ubiqui-

tination (or ubiquitylation), condemns the protein to

proteolysis or other fates such as relocalization or endo-

cytosis [4]. Ubiquitination is mediated by a three-step

enzymatic cascade that consists of the activating (E1),

conjugating (E2), and ligating (E3) enzymes [3�]. Atten-

tion has centered on ubiquitin ligases (E3s) because they

specify the target protein (substrate). On the basis of their

domain and subunit composition, as well as mode of

action, E3s can be classified into four groups [3�]: HEC-

T, RING, U-box, and cullin-RING ligases (CRLs,

Figure 1). E3 ligases mediate the attachment of ubiquitin

to a lysine (Lys) e-amino group on the target protein

either by forming an intermediate, as in the case of

HECT-type ligases, or by acting as a scaffold to bring

the target and E2 into proximity (Figure 1). Ubiquitin can

be conjugated as a monomer or as chains of different

lengths linked by any one of its seven Lys residues. The

linkage-type of the ubiquitin chain specifies the function

it mediates [4]. The best characterized function of ubi-

quitin is mediated by the labeling of a protein with a

ubiquitin chain linked via its Lys48 residue. Proteins

labeled with at least four Lys48-linked ubiquitins are

the favored substrate for proteolysis by the 26S protea-

some, a large, 2.5 MDa multisubunit protein complex

present in the nucleus and cytoplasm.

In this review, we summarize and discuss recent insights

to the role of the ubiquitination system (UBS) in immu-

nity, focusing on E3 ubiquitin ligases, emerging concepts

about their functions, and targeting by pathogen viru-

lence effectors.

CRLs and hormone signalingJasmonic acid (JA)

The COI1 F-box was the first component of the UBS

shown to play a role in plant immunity [5]. The Arabi-dopsis coi1 mutant was originally identified because of its

insensitivity to the bacterial toxin coronatine, and was

later shown to be required for all JA-dependent responses

[6]. JA is synthesized in response to pathogen attack, and

coi1 mutants are unable to relay the JA-signal, making

them more susceptible to necrotrophic pathogens [6].

Two groups recently uncovered the long-sought after

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http://dx.doi.org/10.1016/j.pbi.2010.04.002

Ubiquitination in plant immunity Trujillo and Shirasu 403

Figure 1

E3 ubiquitin ligases categorized by domain. (a) RING and U-box domain

E3 ubiquitin ligases are composed of a single subunit. Both domains are

structurally related and bind the E2-conjugating enzyme–ubiquitin

complex. The RING motif is stabilized by two zinc ions, while the U-box

motif exploits electrostatic interactions. Substrate specificity is

conveyed by various protein–protein interaction domains such as

ankyrin repeats in RING type ligases, and prominently by armadillo-like

(ARM) repeats in U-box ligases. (b) Cullin-RING ligases (CRLs) are

composed of multiple subunits and are composed of a cullin, a RING-

box 1 (RBX1, which binds the E2–ubiquitin complex), and different target

recognition modules. CRLs include the S phase kinase-associated

protein 1 (SKP1)–cullin 1 (CUL1)–F-box (SCF) and bric-a-brac–

tramtrack–broad complex (BTB) ligases. The F-box motif mediates

interactions with the adaptor protein SKP1 in SCF ligases, whereas

additional protein–protein interaction domains are responsible for target

recognition. The modular BTB subunit binds directly to CUL3 via the

BTB domain and specifies the substrate through additional motifs, such

as ankyrin repeats, as in the case of NPR1. (c) HECT domain ligases are

single unit ligases, and in contrast to all other known ubiquitin ligases,

the HECT domain itself binds to ubiquitin before mediating ubiquitination

of a substrate. Thus far, there is no evidence for the involvement of

HECT domain ligases in plant immunity. Numbers in parentheses

indicate the number of predicted proteins in Arabidopsis. For a complete

and detailed account of E3 ligases, please refer to the outstanding

Vierstra review [3�].

missing link in JA signaling, namely the jasmonate ZIM-

domain (JAZ) transcriptional repressors [7��,8��]. Chini

et al. and Thines et al. showed that JAZ proteins are

targeted by SCFCOI1 for proteasomal degradation in a

JA-dependent manner, and that JA-isoleucine (JA-Ile) is

the active form that mediates the recruitment of JAZ

proteins to SCFCOI1 [8��] (Figure 2). A similar mechanism

was observed for SCFTIR1. Auxin binds TIR1, a close

homolog of COI1, and prompts the degradation of the

AUX/IAA transcriptional repressors [9]. Interestingly,

interference with auxin signaling also affects the resist-

ance against necrotrophic pathogens [10].


Salicylic acid (SA)

SA is the key hormone in systemic acquired resistance

(SAR), and is also pivotal for defense responses against

biotrophic and hemibiotrophic pathogens. Spoel and col-

leagues recently showed that the master coactivator of the

SA pathway, NPR1, is continuously degraded in the

nucleus in a proteasome-dependent manner [11��]. Intri-

guingly, SA treatment facilitates recruitment of NPR1 to

a CUL3-based ligase, and proteolysis is required for full

activation of SA marker genes. This process requires the

phosphorylation of NPR1 at residue Ser11/Ser15, show-

ing the importance of phosphorylation to activate, or

enhance the recruitment to proteolytical complexes.

NPR1 contains a broad-complex, tramtrack, and bric-a-

brac (BTB) domain, which is present in CRL substrate

adaptors [3�] (Figure 1). The presence of a BTB domain

raises the possibility that NPR1 itself is actively engaged

in the ubiquitination process. NPR1 coimmunoprecipi-

tates with CUL3A and the interaction is enhanced by SA

[11��]; however, an interaction with CUL3 could not be

detected in a yeast two-hybrid assay [12]. The lack of

post-translational modifications in yeast (on target or

CRL), which are required to regulate the interaction,

may explain these results. CUL3A could possibly recruit

NPR1 via its BTB domain to mediate autoubiquitination,

thereby regulating its own activity by proteolysis

(Figure 2).

It may thus also be possible that NPR1 acts a substrate

adaptor for a BTBNPR1 CRL. In addition to the BTB

domain, NPR1 also contains ankyrin repeats that mediate

protein–protein interactions, as for example, with the

TGA2 transcription factor [13]. TGA2 is a repressor of

PR genes [14] and an activator of genes of the antagonistic

JA pathway [15]. In this scenario, SA would induce a

CUL3-based BTBNPR1 ligase that mediates the degra-

dation of transcriptional repressors such as TGA2 or

NIMIN1 [14,16]. In addition, phosphorylation of NPR1

could switch autoubiquitination activity of BTBNPR1 to

substrate ubiquitination by enhancing its affinity to tar-

gets such as TGA2 (Figure 2). This possibility does not

contradict the observations that NPR1 restricts TGA2

function by interacting with it [14]. NPR1 is able to

sequester TGA2 away from its cognate promoter, negat-

ing its repressor activity and at the same time making it

more accessible to the proteasome. This model would

also agree with the observation that CUL3 and protea-

some activity are necessary for full activation of the

pathway [11��].

Ethylene (ET)

ET biosynthesis is induced in response to PAMPs and

infection by several pathogens. ET apparently fine-tunes

antagonistic SA and JA responses through NPR1 [17].

Ubiquitin-mediated proteolysis is intricately involved in

the regulation of ET perception [18], biosynthesis [19,20],

and signaling [21] (Figure 2). The exact mechanism by


404 Biotic interactions

Figure 2

Ubiquitination and immunity signaling. Attack by necrotrophic pathogens induces the jasmonic acid (JA) pathway. JA-Ile, the active form of JA, binds

to COI1 and induces the interaction with the JAZ transcriptional repressors, leading to ubiquitination by SCFCOI1 and proteasomal degradation

followed by the release of MYC2, thus allowing activation of the JA response. Perception of PAMPs and effector proteins induces the salicylic acid

pathway. Pathogen perception leads to changes in the redox status of the cell and induces the monomerization of NPR1. NPR1 relocalization to the

nucleus is accompanied by transcriptional activation of PR genes. NPR1 is proposed to mediate signaling by sequestering transcriptional repressors

(e.g. TGA2). Alternatively, NPR1 could participate in a BTBNPR1 ligase complex that mediates ubiquitination and degradation of repressors. NPR1

function is regulated by phosphorylation, perhaps by affecting substrate affinity and autoubiquitination. Perception of PAMPs or effectors leads to

activation of distinct but related immune responses, referred to as PAMP-triggered immunity (PTI) or effector triggered immunity (ETI). Plasma

membrane or intracellular receptors mediate signaling, which is positively or negatively regulated by different PUBs and RING ligases. Ethylene

biosynthesis is induced by various biotic stresses. The turnover of the ethylene precursor ACC synthases (ACS) 2 and ACS6 is reduced by

phosphorylation leading to increased ET synthesis. Proteolysis of the EIN3 transcriptional factor is under the control of antagonistic pathways. CTR1

promotes phosphorylation that renders EIN3 accessible to degradation, probably by the cognate SCFEBF1/EBF2. Conversely, MAPK3/6 mediates the

stabilization of EIN3. Arrows and bar-headed lines indicate functional interactions, and double-headed arrows indicate a physical interaction. Dotted

forms and arrows denote inferred interactions and components for which data are not available. Light blue arrows indicate ubiquitination, a question

mark (?) indicates an unknown target, yellow dots indicate ubiquitin (U), and red dots indicate phosphorylation (P).

which PAMP perception induces ET biosynthesis is not

known. However, MPK6, which is activated by PAMP

perception, phosphorylates the ET biosynthesis enzymes

1-aminocyclopropane-1-carboxilic acid (ACC) synthase

(ACS) 2 and ACS6, protecting them from proteasome-

mediated degradation [22]. Similarly, protein levels of

ACS4, ACS5, and ACS9, which belong to the type 2 ACSs,

are also under proteolytic control via the BTB domain E3

subunits ethylene-overproducing 1 (ETO1) and ETO-like

1 (EOL1) and EOL2 [20].


The central ethylene signaling hub, ethylene insensi-

tive 3 (EIN3), was recently reported to be under the

control of bifurcating and antagonistic MAPK cascades

[23��]. MPK6 phosphorylates EIN3 at its threonine

(Thr) 174 residue, rendering it susceptible to degra-

dation, probably by the cognate SCFEBF1/EBF2 [9]

(Figure 2). By contrast, MPK6-independent phos-

phorylation of the Thr592 residue protects EIN3 from

degradation, illustrating the importance of UBS in the

ET pathway.



Cross-talk between ET and PAMP-triggered signaling

was recently shown to involve the stability of the ET-

responsive element binding factor 104 (ERF104). Per-

ception of the conserved peptide from the PAMP flagel-

lin, flg22, induces phosphorylation and release of ERF104

from a complex with MPK6, which results in enhanced

turnover [24�]. Furthermore, mutation of the phosphoryl-

ation site further reduces ERF104 stability, indicating

that modification of the target is important for regulating

ubiquitination followed by proteasomal degradation.

RINGs and PUBs in early immune responsesRING and Plant U-box type (PUB) E3 ligases involved in

immunity have been identified mainly by transcript pro-

filing of genes rapidly induced by biotic cues. This

circumstantial evidence led to the identification of

numerous homologs and orthologs in different plant

species [25–27]. The gene family ‘Arabidopsis toxicos paralevadura’ (ATL), coding for putative RING-type ligases,

has been proposed to play a role in immunity because

some of its members are induced by the PAMP chitin

[28]. However, a role in immunity for this gene family has

only been confirmed for ATL9 (At2g35000) since the atl9mutants are more susceptible to the biotrophic fungus

Erysiphe cichoracearum [27]. A related ATL gene in tomato,

RING finger protein 1 (RFP1), is necessary for resistance

against the necrotrophic pathogen Phytophthora infestans[29], suggesting a conserved role for the ATL gene family.

Notably, transcriptional induction of ATLs is not only

restricted to chitin, but also observed for other PAMPs

[26,30]. Nevertheless, despite the large number of RING-

type genes in Arabidopsis (477), few have been shown to

have a function in immunity.

Several PUBs have been documented as positive and

negative regulators of immune responses in different

plant species. For example, the Avr9/Cf9 rapidly elicited

(ACRE) genes ACRE74 (CMPG1) and ACRE276 (PUB17)

are required for the hypersensitive response, a pro-

grammed cell death-type reaction, in response to percep-

tion of the Avr9 peptide by the Cf9 receptor-like protein

in tobacco [31�,32�] (Figure 2). Further supporting their

role in resistance, tomato knock-down lines are more

susceptible to the biotrophic fungus Cladosporium fulvum.

In addition, the two closely related U-box proteins M-

AC3A and MAC3B are required to mount an effective

defense response against several virulent and avirulent

biotrophic and hemibiotrophic pathogens [33]. MAC3A

and MAC3B are not strongly induced by biotic cues, and

show homology to yeast and human Prp19 ubiquitin

ligases involved in RNA processing, suggesting a prob-

able role in the regulation of gene expression (Figure 2).

By contrast, three closely related E3 ligases, PUB22,

PUB23, and PUB24 negatively regulate PAMP-triggered

signaling and PTI cumulatively [34��] (Figure 2). Inter-


estingly, the pub22/23/24 triple mutant reacts with an

enhanced oxidative burst to various PAMPs, indicating

that these E3 ligases have a function in a process shared

by distinct pattern recognition receptors required for

downregulation of signaling. The closest homologs to

NtACRE74 in Arabidopsis are PUB20 and PUB21, which,

together with PUB22–PUB24, are conspicuously induced

by many biotic stresses and pathogen attack, suggesting

that they also perform a function in immunity. Analysis of

pub21 and pub22 mutants has revealed that these two are

also negative regulators of PAMP-triggered immunity

(our unpublished results), which contrasts to the function

of their homolog ACRE74 in tomato and in tobacco [31�].Mutants of the Lotus japonicus CERBERUS, a U-box

encoding gene, produce more prenodule structures in

response to infection by Rhizobium bacteria, but are

unable to support the formation of an infection thread,

suggesting a function in the negative regulation of nodu-

lation and possibly of immunity [35].

In comparison to CRLs, little is known about the sub-

strates of PUBs and RING ligases, and therefore the

cellular processes they participate in. However, there

are a few exceptions that can provide some clues. The

rice XA21 binding protein 3 (XB3) is a RING ligase which

is phosphorylated by the kinase domain of the PRR XA21

in vitro [36�]. Reduced transcript levels of XB3 in trans-

genic plants lead to an increase in susceptibility to the

avirulent Xanthomonas oryzae pv. oryzae [36�]. Although

unrelated in function, several PUBs in Arabidopsis interact

with S-type receptors, which mediate self-incompatibility

in Brassica and a chitinase-related receptor-like kinase in

tobacco [37,38]. Whether these E3 ligases are able to

ubiquitinate the receptors or phosphorylation controls

their activity are still open questions.

In mammals, RING and U-box proteins, although diver-

gent in domain composition, also function as E3 ligases,

and are regulatory components of both innate and adaptive

immunity. Most notably, TNF receptor-associated factor

(TRAF) 6 catalyses Lys63-linked polyubiquitin chains,

leading to the activation of downstream signaling com-

ponents [39]. TRAF6 is also targeted for Lys63 polyubi-

quitination by Act1, a U-box-containing ligase required for

Interleukin-17 signaling [40]. Importantly, endocytosis of

receptor tyrosine kinases, such as the epidermal growth

factor receptor (EGFR), is also regulated by Lys63 ubiqui-

tination by the Cbl RING ligase [41]. EGFR is structurally

related to the plant PRRs, and endocytosis of PRRs

has been shown [42], opening the possibility that such

processes are conserved in plants.

Virulence effectorsThe UBS is heavily targeted by pathogen virulence

effector proteins and virulence compounds. In many

cases, effector proteins co-opt coopt the UBS [43]. The

bacterial effector AvrPtoB from Pseudomonas syringe pv.



tomato, is probably the best studied example. The

C-terminal domain of AvrPtoB displays structural

homology to U-box/RING domains and is an active

ubiquitin ligase [44��]. In its host tomato, AvrPtoB

ubiquitinates the kinase Fen, which is required for

resistance, and targets it for degradation [43]. AvrPtoB

also ubiquitinates other kinase domains, such as those from

the PRRs FLS2 and CERK1 in Arabidopsis [45��,46��],targeting them for degradation. In the case of FLS2,

degradation is sensitive to the proteasomal inhibitor

MG132, but in the case of CERK1, degradation is sensitive

to bafilomycin A, which inhibits vacuolar degradation,

suggesting different preferences for degradation pathways.

Moreover, a whole spectrum of effector proteins can

be found in plant pathogens that covers any aspect of

ubiquitination. The Agrobacterium tumefaciens VirF was

the first identified effector that functions as an F-box. It

hijacks a host CRL, targeting VIP1 and VirE2 which are

bound to the transfer-DNA for the degradation and thus

liberates it to allow integration into the host genome [47].

Other effectors, such as HopM1, promote degradation of

the adenosine diphosphate-ribosylation factor-guanine

nucleotide exchange factor AtMIN7, probably by func-

tioning as adaptors of the UBS [48]. Conversely, there are

also virulence factors that display ubiquitin or ubiquitin-

like modifier protease activity such as XopD which belongs

to the widely distributed YopJ effector family [49].

Pathogens are also capable of manipulating the UBS by

synthesizing virulence molecules that are recognized by

the host, such as hormones or hormone analogs [50]. The

bacterial toxin coronatine binds to the CRL subunit COI1

and activates the degradation of JAZ transcriptional

repressors [7��]. By synthesizing coronatine, bacteria

are able to suppress PAMP-triggered stomata closure,

and induce the JA pathway, which is antagonistic to

the SA pathway, required for PTI [51]. In another such

example, the necrotrophic fungus Gibberella fujikuroi, the

causal agent of the foolish-seedling disease of rice, makes

gibberellins. Treatment of plants with flg22 results in the

stabilization of DELLA proteins, which mediate gibber-

ellin signaling and importantly, flg22 also increases resist-

ance against necrotrophs [52,53]. Therefore, gibberellin

might act as a virulence factor by counteracting DELLA

stabilization induced by other PAMPs such as chitin. In

other cases, virulence molecules, such as syringolin A,

produced by P. syringae pv. syringae, are able to inhibit

proteasomal function [54]. However, how this might be of

advantage to the pathogen is yet unknown.

Conclusions and outlookIt is tempting to speculate that the vast expansion of the

plant UBS, especially of the E3 ligases, encoded by more

than 1400 genes in Arabidopsis, is in part due to the

constant attempts of manipulation by pathogens. Expan-

sion of genes coding for proteins targeted by pathogens,

presumably by duplication, would relax the constraints


posed by effectors or virulence compounds on UBS and

proteasome, especially in light of the fact that plants lack

an adaptive immune system. It is conceivable that some

ligases have evolved to act as decoys [55]. One important

aspect of such a model is that it would assure the stability

of the UBS network in the event that one or several of its

components were being manipulated by pathogens.

Alternatively, it is feasible that some ligases have evolved

to recognize effector proteins and to mediate their

neutralization by ubiquitination, thus targeting them

for degradation.

Future work will reveal the targets of PUB and RING

single-unit ligases and therefore the cellular processes

that they regulate. In contrast to CRLs, U-box and RING

domains, which mediate E2 interactions, show variation

between the main conserved residues. In fact, PUBs and

RING ligases are able to interact with more than one E2

[56,57�]. The E2–E3 combination determines the type of

polyubiquitin linkage, opening the possibility that these

ligases mediate noncanonical ubiquitination, such as

Lys63 polyubiquitination or monoubiquitination, and

thus regulate signaling by proteasome-independent ways.

In contrast, hormone signaling often involves the regu-

lation of transcriptional activators or repressors via turn-

over using CRLs. CRLs use RBX1 as an E2 adapter,

indicating interaction with only a small subset of E2s,

supporting the concept of a specialized role for CRLs in

Lys48 polyubiquitination.

Several studies have demonstrated the importance of

phosphorylation in regulating ubiquitination. This can

take place at the level of the UBS components and at the

substrate level. Although the former has not been shown

to play a major role for CRLs, which are mainly regulated

by other modifications, it could be relevant for PUB and

RING ligases. PUBs were shown to interact with kinase

domains of receptors [37,38], and XA21 phosphorylates

the RING ligase OsXB3 [36�], possibly indicating that

phosphorylation of single unit ligases is implicated in

their regulation. Conversely, phosphorylation clearly con-

trols the turnover of proteins, for example, ERF104 [24�],ACS2/6 [22], NPR1 [11��], and EIN3 [23��] (Figure 2).

Introduction of negative charges by phosphorylation

possibly changes the attributes of the substrate, making

it recognizable to the E3, or promoting the interaction.

An in-depth understanding of the UBS and target recog-

nition, in addition to the virulence stratagems employed

by pathogens to manipulate the system, should prove

useful to develop new strategies and tools to improve

resistance and other traits of crop plants.

AcknowledgementsWe thank Rebecca Lyons for critical reading of the manuscript. Research inKen Shirasu’s laboratory is funded by KAKENHI 19678001 and in MarcoTrujillo’s lab by the Deutsche Forschungsgemeinschaft SFB 567.



References and recommended readingPapers of particular interest, published within the period of review,have been highlighted as:

� of special interest

�� of outstanding interest

1. Jones JD, Dangl JL: The plant immune system. Nature 2006,444:323-329.

2. Pieterse CMJ, Leon-Reyes A, Van der Ent S, Van Wees SCM:Networking by small-molecule hormones in plant immunity.Nat Chem Biol 2009, 5:308-316.

3.�

Vierstra RD: The ubiquitin–26S proteasome system at thenexus of plant biology. Nat Rev Mol Cell Biol 2009, 10:385-397.

An excellent review about the current understanding of the ubiquitinationsystem and the various roles it plays including hormone signaling,morphogenesis, epigenetics, and self-incompatibility.

4. Ikeda F, Dikic I: Atypical ubiquitin chains: new molecularsignals, ‘protein modifications: beyond the usual suspects’review series. EMBO Rep 2008, 9:536-542.

5. Xie DX, Feys BF, James S, Nieto-Rostro M, Turner JG: COI1: anArabidopsis gene required for jasmonate-regulated defenseand fertility. Science 1998, 280:1091-1094.

6. Thomma BPHJ, Eggermont K, Penninckx IAMA, Mauch-Mani B,Vogelsang R, Cammue BPA, Broekaert WF: Separatejasmonate-dependent and salicylate-dependent defense-response pathways in Arabidopsis are essential for resistanceto distinct microbial pathogens. Proc Natl Acad Sci U S A 1998,95:15107-15111.

7.��

Chini A, Fonseca S, Fernandez G, Adie B, Chico JM, Lorenzo O,Garcia-Casado G, Lopez-Vidriero I, Lozano FM, Ponce MR et al.:The JAZ family of repressors is the missing link in jasmonatesignalling. Nature 2007, 448:666-671.

Through the use of forward genetics the authors identify JAZ proteins astargets of SCFCOI1. The authors demonstrate that JAI3 and other JAZs aredirect targets of the SCFCOI1 E3 ubiquitin ligase and JA treatment inducestheir proteasome degradation.

8.��

Thines B, Katsir L, Melotto M, Niu Y, Mandaokar A, Liu G,Nomura K, He SY, Howe GA, Browse J: JAZ repressor proteinsare targets of the SCFCOI1 complex during jasmonatesignalling. Nature 2007, 448:661-665.

Along with [7��], authors identify the family of JAZ genes that encodenegative regulators of the JA pathway. In vitro pull-down and yeast-two-hybrid assays demonstrate that COI1 interaction with JAZ1 is mediatedby JA-Ile but not by nonconjugated JAs.

9. Santner A, Estelle M: Recent advances and emerging trends inplant hormone signalling. Nature 2009, 459:1071-1078.

10. Llorente F, Muskett P, Sanchez-Vallet A, Lopez G, Ramos B,Sanchez-Rodriguez C, Jorda L, Parker J, Molina A: Repression ofthe auxin response pathway increases Arabidopsissusceptibility to necrotrophic fungi. Mol Plant 2008, 1:496-509.

11.��

Spoel SH, Mou Z, Tada Y, Spivey NW, Genschik P, Dong X:Proteasome-mediated turnover of the transcriptioncoactivator NPR1 plays dual roles in regulating plantimmunity. Cell 2009, 137:860-872.

This article reports the requirement of NPR1 proteasome-mediated degra-dation for target gene induction. They describe the importance of NPR1phosphorylation in the recruitment of CUL3 and promotion of degradation.

12. Dieterle M, Thomann A, Renou JP, Parmentier Y, Cognat V,Lemonnier G, Muller R, Shen WH, Kretsch T, Genschik P:Molecular and functional characterization of ArabidopsisCullin 3A. Plant J 2005, 41:386-399.

13. Despres C, DeLong C, Glaze S, Liu E, Fobert PR: The ArabidopsisNPR1/NIM1 protein enhances the DNA binding activity of asubgroup of the TGA family of bZIP transcription factors.Plant Cell 2000, 12:279-290.

14. Boyle P, Le Su E, Rochon A, Shearer HL, Murmu J, Chu JY,Fobert PR, Despres C: The BTB/POZ domain of the Arabidopsisdisease resistance protein NPR1 interacts with the repressiondomain of TGA2 to negate its function. Plant Cell 2009,21:3700-3713.


15. Zander M, La Camera S, Lamotte O, Metraux JP, Gatz C:Arabidopsis thaliana class-II TGA transcription factors areessential activators of jasmonic acid/ethylene-induceddefense responses. Plant J 2009, 61:200-210.

16. Weigel RR, Pfitzner UM, Gatz C: Interaction of NIMIN1 withNPR1 modulates PR gene expression in Arabidopsis. Plant Cell2005, 17:1279-1291.

17. Leon-Reyes A, Spoel SH, De Lange ES, Abe H, Kobayashi M,Tsuda S, Millenaar FF, Welschen RA, Ritsema T, Pieterse CM:Ethylene modulates the role of NONEXPRESSOR OFPATHOGENESIS-RELATED GENES1 in cross talk betweensalicylate and jasmonate signaling. Plant Physiol 2009,149:1797-1809.

18. Chen YF, Shakeel SN, Bowers J, Zhao XC, Etheridge N,Schaller GE: Ligand-induced degradation of theethylene receptor ETR2 through a proteasome-dependentpathway in Arabidopsis. J Biol Chem 2007,282:24752-24758.

19. Wang KL, Yoshida H, Lurin C, Ecker JR: Regulation of ethylenegas biosynthesis by the Arabidopsis ETO1 protein. Nature2004, 428:945-950.

20. Christians MJ, Gingerich DJ, Hansen M, Binder BM, Kieber JJ,Vierstra RD: The BTB ubiquitin ligases ETO1, EOL1 and EOL2act collectively to regulate ethylene biosynthesis inArabidopsis by controlling type-2 ACC synthase levels. Plant J2009, 57:332-345.

21. Qiao H, Chang KN, Yazaki J, Ecker JR: Interplay betweenethylene, ETP1/ETP2 F-box proteins, and degradation of EIN2triggers ethylene responses in Arabidopsis. Genes Dev 2009,23:512-521.

22. Joo S, Liu Y, Lueth A, Zhang S: MAPK phosphorylation-inducedstabilization of ACS6 protein is mediated by the non-catalyticC-terminal domain, which also contains the cis-determinantfor rapid degradation by the 26S proteasome pathway. Plant J2008, 54:129-140.

23.��

Yoo SD, Cho YH, Tena G, Xiong Y, Sheen J: Dual control ofnuclear EIN3 by bifurcate MAPK cascades in C2H4 signalling.Nature 2008, 451:789-795.

This article identifies the components of two potential MAP kinasecascades that mediate the antagonistic regulation of EIN3 via proteolysis.EIN3 is stabilized when phosphorylated on a particular residue by theMAP kinases MPK3 and MPK6. A second MAPK phosphorylation site onEIN3 promotes EIN3 degradation and CTR1 may play a role in thisphosphorylation.

24.�

Bethke G, Unthan T, Uhrig JF, Poschl Y, Gust AA, Scheel D, Lee J:Flg22 regulates the release of an ethylene response factorsubstrate from MAP kinase 6 in Arabidopsis thalianavia ethylene signaling. Proc Natl Acad Sci U S A 2009,106:8067-8072.

This paper describes a mechanism by which PAMP perception might bytranslated into a response via the interruption of a complex betweenMPK6 and ERF104 by the kinase activation. The release of ERF104 isaccompanied by an increase in turnover regulated by phosphorylation.

25. Durrant WE, Rowland O, Piedras P, Hammond-Kosack KE,Jones JD: cDNA-AFLP reveals a striking overlap in race-specific resistance and wound response gene expressionprofiles. Plant Cell 2000, 12:963-977.

26. Navarro L, Zipfel C, Rowland O, Keller I, Robatzek S, Boller T,Jones JD: The transcriptional innate immune response toflg22, interplay and overlap with Avr gene-dependent defenseresponses and bacterial pathogenesis. Plant Physiol 2004,135:1113-1128.

27. Ramonell K, Berrocal-Lobo M, Koh S, Wan J, Edwards H,Stacey G, Somerville S: Loss-of-function mutations in chitinresponsive genes show increased susceptibility to thepowdery mildew pathogen Erysiphe cichoracearum. PlantPhysiol 2005, 138:1027-1036.

28. Martinez-Garcia M, Garciduenas-Pina C, Guzman P: Geneisolation in Arabidopsis thaliana by conditionaloverexpression of cDNAs toxic to Saccharomyces cerevisiae:identification of a novel early response zinc-finger gene.Mol Gen Genet 1996, 252:587-596.



29. Ni X, Tian Z, Liu J, Song B, Xie C: Cloning and molecularcharacterization of the potato RING finger protein gene StRFP1and its function in potato broad-spectrum resistance againstPhytophthora infestans. J Plant Physiol 2010, 167:488-496.

30. Zipfel C, Kunze G, Chinchilla D, Caniard A, Jones JD, Boller T,Felix G: Perception of the bacterial PAMP EF-Tu by thereceptor EFR restricts Agrobacterium-mediatedtransformation. Cell 2006, 125:749-760.

31.�

Gonzalez-Lamothe R, Tsitsigiannis DI, Ludwig AA, Panicot M,Shirasu K, Jones JD: The U-box protein CMPG1 is required forefficient activation of defense mechanisms triggered bymultiple resistance genes in tobacco and tomato. Plant Cell2006, 18:1067-1083.

The authors demonstrate for the first time the role of a U-box type E3ligase, namely CMPG1 (ACRE74), as a positive regulator of cell deathreactions and resistance against a biotrophic fungus.

32.�

Yang CW, Gonzalez-Lamothe R, Ewan RA, Rowland O, Yoshioka H,Shenton M, Ye H, O’Donnell E, Jones JD, Sadanandom A: The E3ubiquitin ligase activity of arabidopsis PLANT U-BOX17 and itsfunctional tobacco homolog ACRE276 are required for celldeath and defense. Plant Cell 2006, 18:1084-1098.

See annotation to [34��].

33. Monaghan J, Xu F, Gao M, Zhao Q, Palma K, Long C, Chen S,Zhang Y, Li X: Two Prp19-like U-box proteins in the MOS4-associated complex play redundant roles in plant innateimmunity. PLoS Pathog 2009, 5:e1000526.

34.��

Trujillo M, Ichimura K, Casais C, Shirasu K: Negative regulation ofPAMP-triggered immunity by an E3 ubiquitin ligase triplet inArabidopsis. Curr Biol 2008, 18:1396-1401.

In this article, a set of highly related PUBs is shown to act as negativeregulators of PAMP-triggered signaling and resistance against biotrophicand hemibiotrophic pathogens.

35. Yano K, Shibata S, Chen WL, Sato S, Kaneko T, Jurkiewicz A,Sandal N, Banba M, Imaizumi-Anraku H, Kojima T et al.:CERBERUS, a novel U-box protein containing WD-40 repeats, isrequired for formation of the infection thread and noduledevelopment in the legume–Rhizobium symbiosis. Plant J 2009,60:168-180.

36.�

Wang YS, Pi LY, Chen X, Chakrabarty PK, Jiang J, De Leon AL,Liu GZ, Li L, Benny U, Oard J et al.: Rice XA21 binding protein 3 isa ubiquitin ligase required for full Xa21-mediated diseaseresistance. Plant Cell 2006, 18:3635-3646.

The authors show that the rice XA21 binding protein 3 (XB3) is a RING typeubiquitin ligase, which is able to interact with the XA21 receptor. Further-more, Xa21 is capable of phosphorylating XB3 suggesting that it mightregulate its activity.

37. Samuel MA, Mudgil Y, Salt JN, Delmas F, Ramachandran S,Chilelli A, Goring DR: Interactions between the S-domainreceptor kinases and AtPUB-ARM E3 ubiquitin ligasessuggest a conserved signaling pathway in Arabidopsis. PlantPhysiol 2008, 147:2084-2095.

38. Kim M, Cho HS, Kim DM, Lee JH, Pai HS: CHRK1, a chitinase-related receptor-like kinase, interacts with NtPUB4, anarmadillo repeat protein, in tobacco. Biochim Biophys Acta2003, 1651:50-59.

39. Bhoj VG, Chen ZJ: Ubiquitylation in innate and adaptiveimmunity. Nature 2009, 458:430-437.

40. Liu C, Qian W, Qian Y, Giltiay NV, Lu Y, Swaidani S, Misra S,Deng L, Chen ZJ, Li X: Act1, a U-box E3 ubiquitin ligase for IL-17signaling. Sci Signal 2009, 2:ra63.

41. Marmor MD, Yarden Y: Role of protein ubiquitylation inregulating endocytosis of receptor tyrosine kinases.Oncogene 2004, 23:2057-2070.

42. Robatzek S, Chinchilla D, Boller T: Ligand-induced endocytosisof the pattern recognition receptor FLS2 in Arabidopsis. GenesDev 2006, 20:537-542.


43. Spallek T, Robatzek S, Gohre V: How microbes utilize hostubiquitination. Cell Microbiol 2009, 11:1425-1434.

44.��

Janjusevic R, Abramovitch RB, Martin GB, Stebbins CE: Abacterial inhibitor of host programmed cell deathdefenses is an E3 ubiquitin ligase. Science 2006,311:222-226.

This study reveals that AvrPtoB is a RING/U-box-type E3 ubiquitin ligaseby structural analysis and its function in the suppression of celldeath.

45.��

Gohre V, Spallek T, Haweker H, Mersmann S, Mentzel T, Boller T,de Torres M, Mansfield JW, Robatzek S: Plant pattern-recognition receptor FLS2 is directed for degradationby the bacterial ubiquitin ligase AvrPtoB. Curr Biol 2008,18:1824-1832.

In this paper, authors show that the bacterial virulence effector proteinAvrPtoB is able to ubiquitinate the flagellin receptor FLS2 and target it forproteasome degradation.

46.��

Gimenez-Ibanez S, Hann DR, Ntoukakis V, Petutschnig E, Lipka V,Rathjen JP: AvrPtoB targets the LysM receptor kinase CERK1to promote bacterial virulence on plants. Curr Biol 2009,19:423-429.

Similar as in [45��], the authors show that the bacterial virulence effectorprotein AvrPtoB is able to ubiquitinate the CERK1 receptor and target itfor lysosome degradation.

47. Tzfira T, Vaidya M, Citovsky V: Involvement of targetedproteolysis in plant genetic transformation by Agrobacterium.Nature 2004, 431:87-92.

48. Nomura K, Debroy S, Lee YH, Pumplin N, Jones J, He SY: Abacterial virulence protein suppresses host innate immunity tocause plant disease. Science 2006, 313:220-223.

49. Hotson A, Chosed R, Shu H, Orth K, Mudgett MB: Xanthomonastype III effector XopD targets SUMO-conjugated proteins inplanta. Mol Microbiol 2003, 50:377-389.

50. Robert-Seilaniantz A, Navarro L, Bari R, Jones JD: Pathologicalhormone imbalances. Curr Opin Plant Biol 2007, 10:372-379.

51. Melotto M, Underwood W, Koczan J, Nomura K, He SY: Plantstomata function in innate immunity against bacterialinvasion. Cell 2006, 126:969-980.

52. Navarro L, Bari R, Achard P, Lison P, Nemri A, Harberd NP,Jones JD: DELLAs control plant immune responses bymodulating the balance of jasmonic acid and salicylic acidsignaling. Curr Biol 2008, 18:650-655.

53. Ferrari S, Galletti R, Denoux C, De Lorenzo G, Ausubel FM,Dewdney J: Resistance to Botrytis cinerea induced inArabidopsis by elicitors is independent of salicylic acid,ethylene, or jasmonate signaling but requires PHYTOALEXINDEFICIENT3. Plant Physiol 2007, 144:367-379.

54. Groll M, Schellenberg B, Bachmann AS, Archer CR, Huber R,Powell TK, Lindow S, Kaiser M, Dudler R: A plant pathogenvirulence factor inhibits the eukaryotic proteasome by a novelmechanism. Nature 2008, 452:755-758.

55. Shabab M, Shindo T, Gu C, Kaschani F, Pansuriya T, Chintha R,Harzen A, Colby T, Kamoun S, van der Hoorn RA: Fungaleffector protein AVR2 targets diversifying defense-related cysproteases of tomato. Plant Cell 2008, 20:1169-1183.

56. Wiborg J, O’Shea C, Skriver K: Biochemical function of typicaland variant Arabidopsis thaliana U-box E3 ubiquitin-proteinligases. Biochem J 2008, 413:447-457.

57.�

Kraft E, Stone SL, Ma L, Su N, Gao Y, Lau OS, Deng XW, Callis J:Genome analysis and functional characterization of the E2 andRING-type E3 ligase ubiquitination enzymes of Arabidopsis.Plant Physiol 2005, 139:1597-1611.

A detailed functional analysis of the interaction between E2 conjugatingenzymes and RING-type E3 ubiquitin ligases.


Ubiquitination in plant immunity

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