Poster: Photomorphogenesis

Abs # 500: Probing Early Phytochrome Signaling and Transcriptional Networks

Presenter:	Khanna, Rajnish , rajnish@uclink.berkeley.edu
Authors	Khanna, Rajnish  (A) (B)  Tepperman, James M. (A) (B)  Quail, Peter H. (A) (B)
Affiliations:	(A): University of California, Berkeley (B): USDA / Plant Gene Expression Center

Light exerts a profound influence on the growth and development of plants. Early patterns of photomorphogenesis are mediated primarily by adaptational changes in light-regulated gene expression. Oligonucleotide microarray experiments have revealed that phyA may regulate seedling photomorphogenesis by directly influencing the expression of a master set of multiple classes of transcription factor genes. Using reverse genetics, we have now isolated two independent mutant lines for one of the phyA-dependent early-response genes. During this work, this locus was reported to encode ELF4 (Early Flowering 4), involved in photoperiod perception. Here we report that ELF4 is involved in phytochrome mediated signal transduction. ELF4 is an early-response gene regulated by phyA, its function is required for phy mediated photomorphogenesis. Previously, we reported two distinct but similar phy-interacting bHLH factors (PIF3 & PIF4), that bind selectively to the biologically active form of phyB. Sequence similarity studies with PIF3, followed by biochemical analysis and reverse genetics have revealed a novel phy-interacting bHLH factor (PIF5). PIF5 binds specifically to the biologically active form of phyB. While pif5 mutants display a hypersensitive morphological phenotype, the PIF5 (OX) transgenics exhibit a hyposensitive phenotype. In addition, the PIF5 (OX) lines are shorter than the wild type Arabidopsis seedlings grown in the dark, suggesting that PIF5 may have dual functions, suppression of hypocotyl elongation in etiolated seedlings and functioning as a negative regulator of phyB signaling in the light grown seedlings.