Plant Cell Physiol. 136(8): 968–975 (2004) Nature 448 , 358-361 (19 July 2007) The Plant Journal (2005) 44 , 1023–1035
In the dark, PIL5 activates the expression of various genes, including GAI, RGA, and other unknown factors (Xs), by binding directly to their promoters through G-box elements, resulting in increased protein levels of GAI, RGA and X factors. The X factors repress GA biosynthetic and ABA catabolic genes and activate GA catabolic and ABA biosynthetic genes, resulting in decreased GA levels and increased ABA levels. The decrease in GA stabilizes DELLA proteins, leading to increased DELLA protein levels and suppression of GA responses, including testa rupture and subsequent germination. Upon light irradiation, activated phytochromes induce PIL5 degradation, leading to decreased levels of GAI and RGA proteins and ABA. The level of RGL2, although not transcriptionally regulated by PIL5 directly, is also decreased due to the increased bioactive GA. As a result, various physiological processes are initiated, including the mobilization of storage molecules and the hydrolysis of cell walls, and the seeds eventually germinate. Red lines, events occurring at the protein level; blue lines, events occurring at the transcriptional level; green lines, events occurring via enzymatic activities. The potential regulatory circuit between GA and ABA is not shown here.
Phytochrome Interacting Factors Lin Li Chory’s lab
Content <ul><li>Members and structure </li></ul><ul><li>mRNA level, protein level, phenotype of PIFs and PIFs mediated light signaling pathway </li></ul><ul><li>Biological functions of PIFs </li></ul>
Plant Cell. 2008;20(2):337 Quail Lab Plant Cell. 2004 ;16(11):3033 Quail Lab ... Cell. 1998 25;95(5):657 Nature. 1999 19;400(6746):781 Science. 2000 288(5467):859 PNAS. 2000 21;97(24):13419 Quail Lab PIF3 was found using Y2H with PhyB C-term. PIF3 binds only the Pfr form, with 10 times more affinity to PhyB than to PhyA. PIF3 binds to G-box. Phenotype show PIF3 is a positive regulator of Phy signaling. EMBO J. 2002 21(10):2441 Quail lab Mutant srl2 is short under red light , Mutation In PIF4 which can Bind G box. It is a negative regulator. Plant Cell. 2003 15(10):2399 Choi Lab Plant Cell. 2004;16(6):1433 Nagy Lab PNAS. 2004 16;101(46):16091 Quail Lab New PIF3 T-DNA show short hypocotyl under R and real FL OX show long hypocotyl. PIF3 is a negative regulators of Phy signaling. PIF3 is rapidly degraded by light. Science. 2004 305(5692):1937 Quail Lab Indentification of the Phy binding motif (APB motif). Base on the sequence homology, PIF5 and PIF6 are identified. Based on the premise that closely related proteins may have similar functions, a new bHLH family member PIF1 is identified investigate members of the Arabidopsis bHLH subfamily 15 for possible involvement in phy signaling, characterized bHLH072 as PIF7
PIF family members PIF7 At5g61270 bHLH72 +/- R Hypocotyl elongation Cotyledon expansion Trends Plant Sci. 2007 Nov;12(11):514
The APB motif is both necessary and sufficient for binding to the biologically active pfr form of phyB The Plant Cell, 2004 Vol. 16, 3033 ELxxxxGQ PIF7
Physical interactions of PIFs with phy and with other PIFs Modify from Trends Plant Sci. 2007 Nov;12(11):514 PIF7 CACGTG E-box: CANNTG The Plant Cell, 2004 Vol. 16, 3033 PIF7 7 7 7 4 G-BOX 7 7
Most PIFs are degraded in light condition except PIF7 PIF1 PIF4 PIF5 PIF3 PIF7
All PIFs null lines show shorter hypocotyle and OX lines show taller hypocotyl phenotype PIF1 PIF4 and PIF5 PIF3 PIF7
Model of PIF function in phytochrome signaling pathways Nature review 2007 Vol 8;217
Biological functions of PIF1 The Plant Cell, 2007 Vol. 19: 1192 PIF1 is involved in light-induced seed germination , light-induced inhibition of hypocotyl elongation, negative hypocotyl gravitropism in the Dark, Chlorophyll accumulation in light.
Biological functions of PIF3 PNAS 2009 Vol (106) 18; 7655 PIF3 is involved in light-induced inhibition of hypocotyl elongation, chloroplast development, light-induced accumulation of anthocyanin.
PIF4 is involved in hypocotyl elongation Current Biology 2009 Vol 19 No 6 Nature 2008 Vol 451, 480 The Plant Journal (2009) 60, 589
A quadruple mutant (pifq) lacking four PIFs(PIF1, 3, 4, and 5) is constitutively photomorphogenic in darkness : these factors sustain the skotomorphogenic state The Plant Cell, 2009 Vol. 21: 3535
PIF6 is involved in seed dormancy PIF6 is expressed strongly during seed development, and that two splice variants exist, one full length (the a form), and a second, the b form, in which a cryptic intron containing the potential DNA binding domain is spliced out, predicted to lead to the generation of a premature stop codon. Loss of PIF6 increases primary seed dormancy , whereas overexpression of the b form, but not the a form, reduce dormancy.
PIF7 is involved in hypocotyl elongation Plant Physiology, 2009, Vol. 151, 2046
Open questions <ul><li>Identification target genes of PIFs </li></ul><ul><li>How are PIFs involved in hormone signaling </li></ul><ul><li>Regulation of PIFs function </li></ul><ul><li>Circadian and PIFs </li></ul>