Occurrence of Gibberellins in Vascular Plants - Plant Hormones
Gibberellins GAs. a class of plant hormones affect several important plant processes eg., seed...
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Transcript of Gibberellins GAs. a class of plant hormones affect several important plant processes eg., seed...
GibberellinsGAs
a class of plant hormones
affect several important plant processes
eg., seed germination
stem elongation
flowering
male sterility
Gibberellins (GAs)
Gibberellins
1926 Japanese scientist Gibberella fujikuroigibberellin A (terpenoid cpd)
1954, 1955 US and UK scientists1958 GA1 in higher plant
GAx1987 synthesis/metabolism
Gibberellins
1991 84 GAs
1995 89 GAs
64 plants, 12 fungi
13 both
1996 more than 100 / 136
1997 genes being cloned
Gibberellic acid (GA3)
End metabolic product in fungi
Plant GA20 GA5 GA3
Commercial
High activity
Slow degradation
Similar to GA1
additional double bond
Gibberellins
GA4 GA7 nonpolar, slowly diffuse
GA9 GA12 precursor
GA29 GA34 deactivated form
Different tissues
Different forms of GA
fungi algae
bacteria
moss fern
gymnosperm
angiosperm
Gibberellins
growing, differentiated tissues
young, developing, expanding leaves
developing seeds/fruit
Gibberellins
elongated internode/petiole
shoot/stem apex
root cap/tip
xylem sap
Gibberellins
Synthesis and Metabolism
Mevalonic acid pathway
in cytosol
Non mevalonic acid pathway
in plastid
Mevalonic acid pathway
In higher plants
from GA12 aldehyde
Early 13-hydroxylation pathway
(GA1)
Non 13-hydroxylation pathway
(GA4)
with GA20oxidase genes:
pathway shifted
GA4 increased / GA1 decreased
12GA aldehyde: precursor of GA derivatives
20 13 3 2by oxidation (C ) and hydroxylation (C C C )
Vegetative tissue: conserved synthetic pathway
13-OH pathway to GA20 (C19-GA)
then 3-OH to GA1
except: arabidopsis and cucumber
non 13-OH pathway to GA4
Reproductive tissue/seed: various pathways
different forms of GA
From mevalonic acid (6C)
GGPP (20C-linear cpd)
ent kaurene (1st specific cpd)
GA12 aldehyde (first GA)
GAx
Isoprene (5 C) as basic unit
- ent Gibberellane skeleton
tetracyclic diterpenoid cpd
Gibberellins
2 main types:
C20-GA and C19-GA
GA derivatives by modification of 4 rings
* C20 oxidation: CH3 CH2OH CHO COOH
* Hydroxylation at C2 C3 and C13:
number, position
stoichiometry
* Loss of C20 (C20 to C19 GA)
* 2-OH: GA20 GA29
GA1 GA8
* C20 oxidation to COOH
GA inactivation
* Conjugation by glucose
Glycosylation:
inactive, storage and transport
Glucose via COOH: GA glycoside
Glucose via OH: GA glycosyl ether
GA inactivation
GA synthesis mutants
Pea na mutant: dwarf
ent-kaurene GA12 aldehyde
Pea le mutant: dwarf
exogenous GA1 tall
exogenous GA20 no response
cloned Le gene: 3 hydroxylase
GA20 GA1
Considering 2 locina Le normal ent-kaureneNa le normal GA20
Grafting1. na Le scion
Na le stock tall
2. Na le scionNa Le stock dwarf
Conclusion?
Unlike auxin (acidification)
Increase wall extensibility
Decrease minimum force
for wall extension
GA mechanism in elongation
By (may)
decrease Ca concentration in the wall
increase Ca uptake into the cell
reduce crosslinking of lignin-related cpd
(via peroxidase)
GA mechanism in elongation
GA mechanism in germination
Activate transcription of
amylase gene
In scutellum and aleurone
GA detection and assayBioassay
Easy but not specificFractionation Plant response
Lettuce hypocotyls elongationMicrodrop/dwarf rice amylase production
GC-MSSolvent extraction
Chromatography (polarity)
GC (boiling point)
MS (mass)
Identification and quantification
High sensitivity and more specific
Inhibit ent-kaurene synthesis
AMO1618
Cycocel
Inhibit ent-kaurene oxidation
PaclobutrazolUniconazol
Ancymidol Tetcyclasis
Inhibit later steps by dioxygenases
Bx-1112
LAB1988999
GA inhibitors
Hormone Responses
Perception: receptor
Signal transduction:
second messenger (cAMP, cGMP)
G protein
Ca-Calmodulin
enzyme
transcription factor
At last step
Gene expression
Specific region in promoter
cis element
DNA-binding protein
transcription factor
Exogenous GA / GA inhibitor
GA mutant
Gene identification / Gene cloning
Gene expression / Transformation
GA studies
Enzyme: gene product of multigene family
Each gene with specific pattern of expression
AtGA20ox1: shoot growth
AtGA20ox2: inflorescence development
AtGA20ox3: early seedling development
GA synthesis
Genes controlled by GA, light and daylength
GA: inhibit transcription of GA20oxidase
(GA19 to GA20)
inhibit 3 hydroxylase
promote 2 hydroxylase
At later steps of synthetic pathway
Light : promote conversion of GA1 to inactive GA8
reducing shootelongation
N NNNNNNN NNNNNNNN 20 1: reduce production of active GA and GADaylength (LD): floral initiation
activates GA20oxidase activity
GA53 to GA44
GA19 to GA20
Lettuce: Lactuca sativa seed germination
Red light: activates LsGA3ox1 expression
GA1 increase
Far-red light: inhibits LsGA3ox1
NNNNN 1: promote GA production
29 8inhibit deactivation steps to GA and GA
N NNN Pisum sativumNN NN-NNNNNNNNN NNN NNNNNNNNN NNNNNNN NN NNNN NNNNN NNN NNN 1, all reduce GA level
Arabidopsis:
seed germination assay
5 complementation groups (56 lines)
ga1 ga2 ga3 ga4 and ga5
all recessive, dwarf, and male sterile
ga1 and ga2 reversed by ent-kaurene
ga3 reversed by ent-kaurenal
GA synthetic mutants
GA1 kaurene synthase (ent-CDP synthase)
GA3 Cyt P450-dependent monooxygenase
GA4 3 hydroxylase
GA5 GA20oxidase
Genes
Pea (sln)
decrease 2 hydroxylase activity
increase active GA
tall plant with light green leaves
Signal transduction mutants
Stature mutants
Decreased response to GA
Increased response to GA
Dwarf
Complete phenocopy of
GA-deficient mutants
No response to exogenous GA
Decreased signaling mutants
Partially / fully dominant
Arabidopsis gai
Maize D8 D9
Wheat Rht1 Rht2 Rht3
Negative regulators
Decreased signaling mutants
Dwarf
Higher level of active GA
and GA20oxidase
Semidominant
Arabidopsis gai mutant
gai1-151 bp inframe deletionloss of 17 amino acidconstitutive repressor
Arabidopsis gai mutant
Arabidopsis gai mutant
intragenic suppressor of gai
loss of function allele
WT phenotype
Maize D8 mutant
Dwarf
Higher level of active GA
6 dominant alleles
with different severity
8 dominant alleles with different severity
Dwarf: prevent lodging
Wheat + N fertilizer: increase yield
increase height
Norin10: dwarf line
2 mutated loci: Rht1 or Rht-B1b (chrs 4B)
Rht2 or Rht-D1b (chrs 4D)
Wheat Rht mutant
All genes cloned:deduced amino acid sequenceGAI / Rht / d8 homologsConserved domains I and II in N terminal
gai mutant:deletion in domain ID8 / Rht: mutation in domain I and/or II
*N terminal essential for GA response*
Similar to WT + GATall by elongated internodes
Arabidopsis spy rgaBarley sln spyRice slrTomato proPea la crys
Recessive / Negative regulators
Increased signal transduction mutants
Arabidopsis rga
Identified by suppression analysis of ga1-3
New mutant: taller
ga1-3 < ga1-3* < WT
new locus: repressor of ga1-3 (rga)
Increased signal transduction mutants
rga: recessive (deletion mutation)
increase stem elongation
reverse ga1-3 delayed flowering time
no effect on GA biosynthesis
RGA: negative regulator
Gene: 82% homology to GAI
especially in N region
Increased signal transduction mutants
Original gai mutant: gain of function
Loss of function allele of GAI ?
Phenotype: normal
Increase paclobutrazol resistance
Low GA = normal height
At least two components in Arabidopsis GA signaling pathway
N NN NNN NN N
NNNNNN N NNNNNNNNN NNNNNNN/
NNNNNNN NNNNNN NNN NNNNNNN-NNNNNNN NNNNNNNNNNN
NNNNNNNN NNNNNNN NNNNNNNNNN NNNNNN
slender mutant
recessive
long internodes and narrow leaves
male sterile
increase -amylase w/o GA
low endogenous GA
resistant to GA synthesis inhibitors
Barley sln
negative regulator
sln x dwarf mutant = sln phenotype
SLN = GAI/RGA homolog
Dominant allele of SLN mutant
Mutation in N terminal
Dwarf barley
slender rice
recessive
phenocopy of barley sln
1 bp deletion in NLS domain
(nuclear localization signal )
Rice slr
frame shift mutation
stop codon
truncated protein
SLR gene = SLN homolog
Modified SLR:
17 aa deletion in DELLA domain
Transformation: dwarf rice
Rice slr
GA signal component
Dicot / Monocot
GAI RGA Rht d8 SLN SLR
Putative transcription repressor
spindly mutant, recessive
paclobutrazol-resistant
long hypocotyls
light green leaves
early flowering
spy ga1-2 = spy phenotypes
spy gai= spy phenotypes
Arabidopsis spy
SPY gene product:
O-GlcNAc transferase
Signaling molecule
Involved in protein-protein interaction
Negative regulator
Arabidopsis spy
Before responses
Expression of GA-regulated genes:
Protein-DNA interaction
Transcription factor
cis elements
Barley: HvGAMyb
Bind specific sequence in
promoter of -amylase gene
Increase gene expression
Overexpression of HvGAMyb gene
= GA treatment
Transcription factor: GAMyb
Arabidopsis: GAMyb-like genes
AtMyb33 AtMyb65 AtMyb101
Functional homologs of barley GAMyb
Transform barley aleurone with AtMyb33
Activate -amylase production
Arabidopsis: facultative LD plants
Transfer plants from SD to LD
11x increase of GA1
3x increase of GA4
increase AtMyb33 expression
in shoot apex
shoot apex transition to flowering
Potential target for AtMyb
LFY promoter
LEAFY: meristem-identity gene
Evidence AtMyb binding
to a specific 8-bp sequence
in LFY promoter
cis elements
specific regions in promoter
transcription factor binding site
identified by deletion or
site specific mutagenesis:
gene expression after promoter modification
- amylase box: TATCCAT
- GARE: TAACAA/GA
- Pyrimidine box: C/TCTTTTAC/T
Conserved sequences among
GA-regulated genes
GA and -amylase production
Perception at membrane receptors
Increase intracellular Ca
Decrease intracellular pH
Increase [CaM]
Increase cGMP
Increase GAMyb transcription
Increase -amylase activity
Some protein phosphorylation