UCSF

Plants adapt to environmental light conditions by photoreceptor-mediated physiological responses, but the mechanism by which photoreceptors perceive and transduce the signals is still unresolved. Here, we used 2D difference gel electrophoresis (2D DIGE) and mass spectrometry to characterize early molecular events induced by short blue light exposures in etiolated Arabidopsis seedlings. We observed the phosphorylation of phototropin 1 (phot1) and accumulation of weak chloroplast movement under blue light 1 (WEB1) in the membrane fraction after blue light irradiation. Over 50 spots could be observed for the two rows of phot1 spots in the 2-DE gels, and eight novel phosphorylated Ser/Thr sites were identified in the N-terminus and Hinge 1 regions of phot1 in vivo. Blue light caused ubiquitination of phot1, and K526 of phot1 was identified as a putative ubiquitination site. Our study indicates that post-translational modification of phot1 is more complex than previously reported.