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 model 3. Signal sensing domain - Sense external signals and transmits these to rest of transcription complex

1. Kale Ravindra Ramrao

2. Outline
 Stress
 Function of drought inducible genes
 Signal transduction
 Introduction to transcription factors
 TFs Motifs
 Families of plant TFs

3.  What is stress ? Types?
 Stress resistance mechanisms
• Avoidance mechanisms
• Tolerance mechanisms
• Acclimatization
(Bartels and Ramanjulu ., 2005)

4. Functions of Drought inducible genes
Detoxification
enzymes
(catalase)
Protection factors of
Transcription
macromolecules(LEA
proteins, chaperons factors (MYB
etc.) Drought , NAC etc.)
Water channel
Protein protein
Key enzymes for
kinase osmolyte biosynthesis
(proline , sugar etc.)
( Agarwal et al.,2006)

5. 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

6. Transcription Factor Motifs
bZIP Zinc finger Basic Helix-loop-helix

7. 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

8. Model of Hormone-dependent Gene Activation
by Homodimeric Receptors
8

10. Different Families of plant stress TFs
 ERF / AP2
 WRKY
 bZIP
 NAC
 MYB
(Agarwal et al., 2006)

11. AP2 / ERF Family
 It include DREB or CBF for DRE or C repeats
(Agarwal et al., 2006)
 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. (Bartels and Sulumar., 2005)

12. 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)

13. Contd…
Stress Response Related to ERF
(Singh et al., 2002)

14. Contd…
(Yamaguchi and Shinozaki ., 2006)

15. 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(C₂H₂) while group III have fingure
motif(C₂HC)
 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)

16. Classification of WRKY
(Thomas et al., 2000)

17. MeJA
wounding auxin
light
SA Mangnaportae grisea
BTH
OsWRKY45 OsWRKY31
OsWRKY03
NH1
bZIP
GST
RCl-1 PBZ1
ZB8 OsSci2 Os1AA4 Arl1/Crl1
POX22.3 PR1b
PAL peroxidase
Resistance to bacterial blight Resistance to fungal blast
x.oryza Root development
M.grisea
(Khong et al., 2008)

18. 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

19. bZIP Family
 Contain DNA-binding domain rich in basic residues adjacent to
leucin zipper dimerization domain
(Bartels and Ramanjulu., 2005)
 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
(Singh et al., 2002)

20. Contd….
(Singh et al., 2002)

21. 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

22. 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)

23. Contd…
Network of rice tolerance to water deficit
(Khong et al., 2008)

24. 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
(Abe et al,.2003)
 Shows conserved tryptophan residues that form core motif
 In plants first tryptophan replaced by phenylalanine or isoleucine

25. 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)

26. Results :-
Analysis of AtMYB60 expression

27. Light induced stomatal Opening is impaired in the atmyb60-1 Mutant

28. 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
(Yi et al., 2005)
 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
(Schachtmn et al., 1998)

29. Contd….
Networks involving bHLH transcription factors for tolerance to
mineral nutrition

30. CONCLUSION

31. DISCUSSION

32. THANK YOU