Taken together our results indicate that the mutants have a normal gravitropic response in darkness but are deficient for phototropism during long-term irradiation. To test whether the PKS proteins are required for phototropism in etiolated seedlings stimulated by a short blue-light treatment, dark-grown Baohuoside I seedlings were exposed to blue-light pulses (Fig. (phot1) and phototropin 2 (phot2) in null mutants show no phototropic curvature at any blue light fluence rates, whereas the mutant is impaired in phototropism Baohuoside I only at high fluence rates (17, 18). Phot1, NPH3, and RPT2 all are associated with the plasma membrane, particularly in elongating cells (16, 20). NPH3 and RPT2 can physically interact with phot1 and each other (16, 18). Moreover, COLEOPTILE PHOTOTROPISM 1, a rice homologue of NPH3, acts upstream of the redistribution of auxin induced by unilateral illumination of the seedling, further indicating that these proteins function early in this signaling pathway (19). In addition to these components specifically acting in phototropism signaling, establishment of a gradient of auxin responsiveness is required to initiate asymmetric growth associated with not only phototropism, but also gravitropism (21). The phytochromes modulate phototropism through mechanisms that remain to be molecularly elucidated (4, 5). Here we show that the phyA signaling components PHYTOCHROME KINASE SUBSTRATE Rabbit Polyclonal to OR4A15 (PKS) 1 and PKS2 (22) and PKS4, another member of this gene family in (23), are required for phototropism. PKS1 is localized at the plasma membrane and can form a complex with phot1 and NPH3. Physiological analysis of loss-of-function mutants demonstrates that the PKS proteins are necessary for normal phototropism under weak intensities of blue light. Hence our findings define the PKS proteins as components of phot1 signaling and suggest that the PKS proteins may represent a link between phytochrome and phototropin signaling. Results The PKS Proteins Are Crucial for Hypocotyl Phototropism Under Low Fluence Rates of Blue Baohuoside I Light. PKS1 and PKS2 are phytochrome-binding proteins acting as components of the very low fluence response (VLFR) branch of phyA signaling (22, 24). PKS1 expression is transiently induced by light exactly in the elongation zone of the root and hypocotyl (22). Elongation zones consist of cells that elongate in response to tropic stimulations to induce organ curvature (1, 2). Light induction of in the hypocotyl elongation zone (22) and strong up-regulation of by blue light (Fig. 4, which is definitely published as assisting information within the PNAS internet site) prompted us to test the involvement of PKS1 in phototropism. belongs Baohuoside I to a small gene family that appeared in the emergence of angiosperms and consists of four users in ((Fig. 5, which is Baohuoside I definitely published as assisting information within the PNAS internet site) and constructed all possible mutant mixtures among gene. The hypocotyls of seedlings are randomly oriented when irradiated with a low fluence rate of blue light from above, because phyA represses gravitropism and phototropism is completely impaired in the absence of phot1 (6). We required advantage of this obvious phenotype to test whether the PKS proteins play a role in phototropism. The growth orientation profile was identified for all the available loss-of-function single, double, and triple mutants by using WT Col-O, as settings (Fig. 1hypocotyls were even more vertically oriented than the WT, and hypocotyls were randomly oriented (Fig. 1single mutants were subtly less vertically oriented than the WT. This inclination of random growth behavior was more pronounced in double mutants. Interestingly, the growth orientation profile of hypocotyls was as random as with mutants, the mutants responded neither to light direction nor to.