Phytochrome Interacting Factors PIFs

1
Phytochrome Interacting Factors (PIFs) Another
Model for Phytochrome Action.
2
Phytochrome Signaling and Transcriptional Networks
3
Photosensory Functions of PhyA and PhyB
D
Rc
FRc
WT
phyA
phyB
Tepperman et al., 2004
4
TWO-HYBRID SCREENING STRATEGY
phy
BD
HIS3/lacZ
GAL1 UAS
5
Phy Interacting Factors (PIFs)
PIF3 a HLH protein (NDPK2 PKS1)
6
Crystal Structure of DNA-bound PHO4
Helix Loop Helix (HLH) protein
Shimizu et al. (1997) EMBO J. 164689.
7
PIF3 is Necessary for Full Phy-mediated Greening
Response
(Used pif3 mutants to examine pif3 function in
vivo)
Monte et al (2004) PNAS (in press)
8
PIF3
What are the DNA binding sites for PIF3? What
are the target genes for PIF3? Does PIF3
heterodimerize?
9
CCA1 LHY have G-box in promoters
Martinez-Garcia et al (2000) Science 288 859
10
(No Transcript)
11
Phytochromes Translocate into Nucleus in Light  
phyB
phyA
Nagy and Schaefer (2000) EMBO J. 19 157-163.
GFP-tagged Phy proteins
12
Postulated Direct Targeting of Light Signal
to Promoter-Bound PIF
3
PrB
R
P
I
F
3
P
I
F
3
G
-
b
o
x
T
A
T
A
FR
PfrB
PfrB
FR
PrB
NUCLEUS
PfrB
P
I
F
3
P
I
F
3
P
I
C
G
-
b
o
x
T
A
T
A
CYTOPLASM
13
PIF3
Does PIF3 heterodimerize? What is/are the
function of its heterodimer(s)?
14
TWO-HYBRID SCREENING STRATEGY
Y
PIF3
AD
BD
HIS3/lacZ
GAL1 UAS
gt1.5X106 colonies screened 16 initial positives 4
true positives PIF1 and PIF4 are new bHLH
proteins
15
(No Transcript)
16
SUMMARY

• Multiple bHLH proteins selectively interact with
  the Pfr form of Phy(s).
• 2. Interaction of DNA-bound PIF3 with Pfr form of
  PhyB may provide for direct regulation of gene
  expression in response to light.
• 3. PIF3 helps controls greening process, and
  interacts with other PIFs.
• 4. Phy signaling involves direct interaction with
  transcription factors.

17
Proposed Phy-regulated Transcriptional Network
TXN FACTOR GENES
DOWNSTREAM TARGET GENES
CELLULAR/ DEVELOPMENTAL PROCESS
SIGNALING TXL REGULATORS
chlorophyll biosynthesis
?
?
?
cell expansion
?
phenylpropanoid biosynthesis
CHS
HY5
?

RBCS
photosynthesis

CCA1
CCA1

LHY
LHY
phy
circadian rhythms

TOC1-L
TOC1-L

phototropism
RPT2
RPT2
?

photorespiration
DOF
DOF

CO
flowering
CO

G-box DNA motifs in promoters