Both PAR1 and PAR2 Promote Seedling Photomorphogenesis in Multiple Light Signaling Pathways

Plant Physiology,doi: 10.1104/pp.113.?227231

Both PAR1 and PAR2 Promote Seedling Photomorphogenesis in Multiple Light Signaling Pathways

Peng Zhou1, Meifang Song2, Qinghua Yang3, Liang Su4, Pei Hou5, Lin Guo6, Xu Zheng2, Yulin Xi2, Fanhua Meng2, Yang Xiao7, Li Yang2 and Jianping Yang89

Abstract

Arabidopsis seedlings undergo photomorphogenesis in the light and etiolation in the dark. Light-activated photoreceptors transduce the light signals through a series of photomorphogenesis promoting or repressing factors to modulate many developmental processes in plants, such as photomorphogenesis and shade avoidance. CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) is a conserved RING finger E3 ubiquitin ligase, which mediates degradation of several photomorphogenesis promoting factors, including ELONGATED HYPOCOTYL5 (HY5) and LONG HYPOCOTYL IN FAR-RED1 (HFR1), through a 26S proteasome-dependent pathway. PHYTOCHROME RAPIDLY REGULATED 1 (PAR1) was first detected as an early repressed gene in both phytochrome (phy) A-mediated far-red (FR) and phyB-mediated red (R) signaling pathways, and subsequent studies showed that both PAR1 and PAR2 are negative factors of shade avoidance in Arabidopsis. However, the role of PAR1 and PAR2 in seedling de-etiolation and their relationships with other photomorphogenesis promoting and repressing factors are largely unknown. Here, we confirmed that both PAR1 and PAR2 redundantly enhance seedling de-etiolation in multiple photoreceptor signaling pathways. Their transcript abundances are repressed by phyA, phyB, and cryptochrome 1 (CRY1) under FR, R, and blue (B) light conditions, respectively. Both PAR1 and PAR2 act downstream of COP1, and COP1 mediates the degradation of PAR1 and PAR2 through the 26S proteasome pathway. Both PAR1 and PAR2 act in a separate pathway from HY5 and HFR1 under different light conditions, except for sharing in the same pathway with HFR1 under FR light. Together, our results substantiate that PAR1 and PAR2 are positive factors functioning in multiple photoreceptor signaling pathways during seedling de-etiolation.