transcriptional factors in stress tolerance
DESCRIPTION
Transcription factors are modular in structure means constructed with standardized units or dimension allowing flexibility and variety in use. It contain 3 domains as ;1. DNA binding domain – This domain binds to responsive elements present in target DNA. It is conserved region of structure.2. Trans-activation domain – This domain contain binding site for another proteins ( repressor , activator) . This domains do not generate identifiable electron density in the crystallography analysis , which indicates that thay do not form discreate structures and acts as induced fit model3. Signal sensing domain - Sense external signals and transmits these to rest of transcription complexTRANSCRIPT
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Transcriptional Factors in Stress Tolerance
Kale Ravindra Ramrao
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Outline
Stress
Function of drought inducible genes
Signal transduction
Introduction to transcription factors
TFs Motifs
Families of plant TFs
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What is stress ? Types?
Stress resistance mechanisms
• Avoidance mechanisms
• Tolerance mechanisms
• Acclimatization(Bartels and Ramanjulu ., 2005)
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Functions of Drought inducible genes
Drought
Detoxification enzymes (catalase)
Protein kinase
Protection factors of macromolecules(LEA proteins, chaperons
etc.)
Key enzymes for osmolyte biosynthesis
(proline , sugar etc.)
Water channel protein
( Agarwal et al.,2006)
Transcription factors (MYB ,
NAC etc.)
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Introduction to Transcription Factors
TFs are proteins that binds to specific sequence of DNA(cis-
acting)elements in promoter region and regulate transcription
Number of transcription factors depends on genome size
Use different mechanism to up or down regulate gene expression
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Basic Helix-loop-helix bZIP Zinc finger
Transcription Factor Motifs
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Structure of TFs
TFs are modular in structure and contain 3 – domains:
DNA binding domain- DNA sequence binds to TFs is known as responsive elements
Trans-activation domain – Contain binding sites for other proteins
Signal-sensing domain – Sense external signals and transmits these to rest of transcription complex
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8
Model of Hormone-dependent Gene Activation by Homodimeric Receptors
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Different Families of plant stress TFs
ERF / AP2
WRKY
bZIP
NAC
MYB(Agarwal et al., 2006)
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AP2 / ERF Family
It include DREB or CBF for DRE or C repeats
Arabidopsis AP2 proteins classified on the basis of similarities in their
DNA-binding domains
CBF genes coordinate both activation or repression of stress responsive
genes.
(Agarwal et al., 2006)
(Bartels and Sulumar., 2005)
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Contd…
Phenotype for loss-of-function mutants have not yet been reported for any ERF genes
Tsi 1( tobacco stress-inducible gene ) provides direct evidence of regulation of responses t biotic and abiotic stresses through single ERF gene
(Singh et al., 2002)
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Stress Response Related to ERF
(Singh et al., 2002)
Contd…
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Contd…
(Yamaguchi and Shinozaki ., 2006)
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WRKY Family
Presence of zinc fingure motif within WRKY domain
Classification done on the basis of number of WRKY domains and the
feature of their zinc-fingure-motif
Group I and II have same fingure motif(C H ) while group III have fingure ₂ ₂
motif(C HC)₂
cis-acting element for WRKY is W box having sequence (T)
(T)TGAC(C/T)which contain the invariant TGAC core
(Thomas et al., 2000)
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Classification of WRKY
(Thomas et al., 2000)
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(Khong et al., 2008)
Role of WRKY in Resistance Against stresses
MeJA
OsWRKY03
NH1
bZIP
ZB8 POX22.3 PR1b
OsWRKY45
GST
Resistance to bacterial blightx.oryza
Resistance to fungal blastM.grisea
light
OsWRKY31
auxin
Mangnaportae griseaSA BTH
PBZ1 OsSci2 Os1AA4 Arl1/Crl1
PAL peroxidase
Root development
wounding
RCl-1
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Contd….
OsWRKY03 act upstream of the the NPR1/NH1 regulation pathway.
OsWRKY45 acts independent of NPR1/NH1
Expression of gene RCL-1 in response to BTH is independent of
OsWRKY45 and NH1
OsWRKY31 links activation and inhibition of plant growth
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bZIP Family
Contain DNA-binding domain rich in basic residues adjacent to leucin zipper dimerization domain
Binds to ACGT (G –box motif ) core sequence
One class of it is TGA/OBF binds to activation sequence-1 / ocs element
TGA/OBF interact with NPR1 a key component of SA defense signaling pathway
(Bartels and Ramanjulu., 2005)
(Singh et al., 2002)
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Contd….
(Singh et al., 2002)
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Contd….
Different TGA / OBF members may involved in different stress responses
Other class include ABF/ AREB that work thorough ABA dependent signal transduction pathway
bZIP shows complexity in regulation that shows pathogen responses override UV protection
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NAC Family Of TF
Plant specific NAC (NAM , ATAF1/2) TFs play diverse roles in plant
development and stress response
NAC family is essential to the activation of the ERD1 gene
OsNAC 1 involved in stress resistance in rice
Expression study of GFP placed under the control of OsNAC1 promoter in
plant , shows that this gene is normally expressed in ligulae , stamen and
in guard cells of stomata
(Khong et al., 2008)
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Contd…
(Khong et al., 2008)
Network of rice tolerance to water deficit
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MYB Family Of TF
MYB proteins from animal contain 3 repeats while plant MYB contain 2
repeats
It carry out expression of ABA-related gene and jasmonic acid-related
genes which shows cross talk pathway between abiotic and biotic stress
Shows conserved tryptophan residues that form core motif
In plants first tryptophan replaced by phenylalanine or isoleucine
(Abe et al,.2003)
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Functions of MYB
1. Phenylpropanoid metabolism
2. Cell shape –
MIXTA and it’s orthologous PhMYB1 gene.
GL1 gene from Arabidopsis
3. Response to hormones –
GA application induce expression of barely MYB protein (GAMYB)
(Cathie and Javier ., 1997)
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Analysis of AtMYB60 expression
Results :-
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Light induced stomatal Opening is impaired in the atmyb60-1 Mutant
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bHLH Family Of TF
In A.thalinia a Myb transcription factor encoded by PHR1 participate in Pi starvation signalling pathway
Os PTF1 from rice has been isolated from a cDNA library obtained from roots of plants cultured in normal or Pi-deficient condition
Os PTF1 acts on the cues of Pi uptake by stimulation root growth resulting in an increase in root surface area
Os PTF1 regulate genes that play ole in Pi starvation rescue but no high affinity Pi transporter genes found
(Yi et al., 2005)
(Schachtmn et al., 1998)
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Networks involving bHLH transcription factors for tolerance to mineral nutrition
Contd….
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CONCLUSION
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DISCUSSION
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