WAVH1, encoding a RING-H2 type E3 ubiquitin ligase, positively regulates the light-induced cotyledon opening in Arabidopsis
Y. BAI , V. PHAM, E. HUQ
Department of Molecular Biosciences, The University of Texas at Austin, 100 East 24th St., Austin, TX 78712-1095, USA

Light as one of the most important environmental factors affecting plant growth and development. During the transition from skotomorphogenic to photomorphogenic development, optimum cotyledon opening is crucial as opened cotyledon makes maximum utilization of sunlight to produce food and energy through photosynthesis. In Arabidopsis, PIF3 (Phytochrome-Interacting Factors 3) plays a vital role in regulating the cotyledon opening. PIF3 is abundant under dark, and upon light exposure, it will be degraded rapidly to modulate cotyledon opening. However, the detailed mechanism of cotyledon opening is less known. In our study, we found WAVH1 , encoding a RING-H2 type E3 ubiquitin ligase, positively regulates the light-induced cotyledon opening. WAVH1 mutant lines showed a delayed cotyledon opening phenotype when exposed to light. Under lower red light fluence rate, WAVH1 mutant lines have a smaller cotyledon than Col-0. WAVH1 can interact with PIF3 both in vivo and in vitro. When exposed to the red light, PIF3 protein level is significantly lower in WAVH1 overexpression line and higher in the wavh1 mutant line compared to WT. Therefore, WAVH1 might regulate the cotyledon opening through the degradation of PIF3. Overall, these data suggest that WAVH1 is a crucial factor regulating the cotyledon opening under light.