Analysis of phototropin family signal pathway in chloroplast relocation movement

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Phototropin family is a photoreceptor for chloroplast avoidance and accumulation movement, phototropism and leaf flatting. In Arabidopsis, the phototropin consist with two LOV domain and kinase. In fern Adinatum capilus-veneris has two phototropin genes and unique phototropin gene, NEO1. The C-terminus of NEO1 shares high homology with the full length sequence of the phototropin, although the first third of the N-terminus is similar to the light-absorbing domain of phytochrome.To understand phot2 function in Arabidopsis, we examined whether phot2 accumulation levels affect phototropin-regulated BL responses including chloroplast avoidance movement. The avoidance velocity increased with the accumulation of more phot2-GFP fusion protein or with a rise in the fluence rate of irradiation. These results suggest that not only is the amount of phot2 normally enough but also the components of the signaling pathway have accumulated sufficiently. As with the chloroplast avoidance movement, phot2-regulated phototropism was also found to have a dependency on phot2 accumulation. However, the transgenic lines that showed P2G accumulation less than phot2 amounts of WT were saturated flatten level of leaves. Therefore, it is unknown that leaf flattening was dependent on phot2 amounts.The phytochrome-light-absorbing region of neochrome 1 with phytochromobilin showed typical red/far-red light photoreversibility and dark reversion of the Pfr form with a half life of about 30 min. The entire photosensory region of phytochrome 3, which consists of the phytochrome-light-absorbing region and the LOV domains showed photoreversibility and the phytochrome photoconversion was not affected by the LOV domains. Though blue light irradiation induced photobleaching of the LOV domains and Pfr formation, the LOV domains did not contribute to Pfr formation. These results indicate that the phytochrome light-absorbing region and LOV domains are independent for light absorption.