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
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
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
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)
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)
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)
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)
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)
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)