Abstract
NRL (NPH3/RPT2-like) family protein RPT2 is an adaptor protein, which harbors a BTB domain and a coild-coil motif and shows an ability to bind to the phot1 blue light (BL) photoreceptor. To reveal the function of RPT2 in phototropism, we have analyzed regulatory mechanisms of RPT2 expression. Our previous study had already indicated that RPT2 mRNA is quickly induced by blue light irradiation. In this study, we reveal that its transcriptional induction is dependent upon activations of photoreceptors of phytochromes (phy) or cryptochromes (cry). A phyA cry1 cry2 triple mutant shows a remarkable decrease in phototropic curvature under high fluence rates of BL, similar to the rpt2 mutant, and constitutive expression of RPT2 partially complements its defect in phyA cry1 cry2 (Tsuchida-Mayama et al. [2010] Plant J. 62, 653). Furthermore, our immunoblot analysis indicates that an activation of phot1 is necessary for an accumulation of RPT2 proteins. These results demonstrate that analysis of regulatory mechanisms of RPT2 expression is significant for understanding of function of phy, cry, and phot in phototropism.
