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Title: ISOLATION AND CHARACTERIZATION OF PHYC MUTANTS IN ARABIDOPSIS REVEALS COMPLEX CROSSTALK BETWEEN PHTOCHROME SIGNALING PATHWAYS

Author
item MONTE, ELENA - UCB-ARS PLNT GENE EXP CTR
item ALONSO, JOSE - PLANT BIOL, SALK INST
item ECKER, JOSEPH - PLANT BIOL, SALK INST
item ZHANG, YUELIN - MAXYGEN INC REDWOOD CTY C
item YOUNG, JEFF - UNIV WISCONSIN, MADISON
item AUSTIN-PHILLIPS, SANDRA - UNIV WISCONSIN, MADISON
item QUAIL, PETER - UCB-ARS PLNT GENE EXP CTR

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2003
Publication Date: 9/1/2003
Citation: MONTE, E., ALONSO, J.M., ECKER, J.R., ZHANG, Y., YOUNG, J., AUSTIN-PHILLIPS, S., QUAIL, P.H. ISOLATION AND CHARACTERIZATION OF PHYC MUTANTS IN ARABIDOPSIS REVEALS COMPLEX CROSSTALK BETWEEN PHTOCHROME SIGNALING PATHWAYS. THE PLANT CELL. 2003. 15:1962-1980.

Interpretive Summary: Studies with mutants in four members of the five-membered Arabidopsis phytochrome (phy) family (phyA, phyB, phyD, and phyE) have revealed differential functions among them, but identification of a phyC mutant has proven elusive. We report here the isolation of phyC mutants and show that phyC is involved in controlling plant responses to light.

Technical Abstract: Studies with mutants in four members of the five-membered Arabidopsis phytochrome (phy) family (phyA, phyB, phyD, and phyE) have revealed differential photosensory and/or physiological functions among them, but identification of a phyC mutant has proven elusive. We now report the isolation of multiple phyC mutant alleles using reverse-genetics strategies. Molecular analysis shows that these mutants have undetectable levels of phyC protein, suggesting that they are null for the photoreceptor. phyC mutant seedlings were indistinguishable from wild-type seedlings under constant far-red light (FRc), and phyC deficiency had no effect in the phyA mutant background under FRc, suggesting that phyC does not participate in the control of seedling deetiolation under FRc. However, when grown under constant red light (Rc), phyC seedlings exhibited a partial loss of sensitivity, observable as longer hypocotyls and smaller cotyledons than those seen in the wild type. Although less severe, this phenotype resembles the effect of phyB mutations on photoresponsiveness, indicating that both photoreceptors function in regulating seedling deetiolation in response to Rc. On the other hand, phyB phyC double mutants did not show any apparent decrease in sensitivity to Rc compared with phyB seedlings, indicating that the phyC mutation in the phyB-deficient background does not have an additive effect. These results suggest that phyB is necessary for phyC function. This functional dependence correlates with constitutively lower levels of phyC observed in the phyB mutant compared with the wild type, a decrease that seems to be regulated post-transcriptionally. phyC mutants flowered early when grown in short-day photoperiods, indicating that phyC plays a role in the perception of daylength. phyB phyC double mutant plants flowered similarly to phyB plants, indicating that in the phyB background, phyC deficiency does not further accelerate flowering. Under long-day photoperiods, phyA phyC double mutant plants flowered later than phyA plants, suggesting that phyC is able to promote flowering in the absence of phyA. Together, these results suggest that phyC is involved in photomorphogenesis throughout the life cycle of the plant, with a photosensory specificity similar to that of phyB/D/E and with a complex pattern of differential crosstalk with phyA and phyB in the photoregulation of multiple developmental processes.