title: Arabidopsis ROOT PHOTOTROPISM2 Contributes to the Adaptation to High-Intensity Light in Phototropic Responses.
abstract: Living organisms adapt to changing light environments via mechanisms that enhance photosensitivity under darkness and attenuate photosensitivity under bright light conditions. In hypocotyl phototropism, phototropin1 (phot1) blue light photoreceptors mediate both the pulse light-induced, first positive phototropism and the continuous light-induced, second positive phototropism, suggesting the existence of a mechanism that alters their photosensitivity. Here, we show that light induction of ROOT PHOTOTROPISM2 (RPT2) underlies photosensory adaptation in hypocotyl phototropism of Arabidopsis thaliana. rpt2 loss-of-function mutants exhibited increased photosensitivity to very low fluence blue light but were insensitive to low fluence blue light. Expression of RPT2 prior to phototropic stimulation in etiolated seedlings reduced photosensitivity during first positive phototropism and accelerated second positive phototropism. Our microscopy and biochemical analyses indicated that blue light irradiation causes dephosphorylation of NONPHOTOTROPIC HYPOCOTYL3 (NPH3) proteins and mediates their release from the plasma membrane. These phenomena correlate closely with the desensitization of phot1 signaling during the transition period from first positive phototropism to second positive phototropism. RPT2 modulated the phosphorylation of NPH3 and promoted reconstruction of the phot1-NPH3 complex on the plasma membrane. We conclude that photosensitivity is increased in the absence of RPT2 and that this results in the desensitization of phot1. Light-mediated induction of RPT2 then reduces the photosensitivity of phot1, which is required for second positive phototropism under bright light conditions.
authors: Department of Human Science and Common Education, Nippon Institute of Technology, Miyashiro-cho, Minamisaitama-gun, Saitama 345-8501, Japan.
authors: Ken
authors: K
authors: Haga
authors: RIKEN Plant Science Center, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
authors: Tomoko
authors: T
authors: Tsuchida-Mayama
authors: Graduate School of Science and Technology, Niigata University, Nishi-ku, Niigata 950-2181, Japan.
authors: Mizuki
authors: M
authors: Yamada
authors: Graduate School of Science and Technology, Niigata University, Nishi-ku, Niigata 950-2181, Japan tsakai@gs.niigata-u.ac.jp.
authors: Tatsuya
authors: T
authors: Sakai
mesh_terms: D017360:Arabidopsis / Q000378:metabolism* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D008027:Light; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D018524:Phototropism / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases
chemical_list: D029681:Arabidopsis Proteins; C400222:NPH3 protein, Arabidopsis; D010750:Phosphoproteins; C405209:RPT2 protein, Arabidopsis; C103646:NPH1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases