Light-Regulated Alternative Splicing of Pseudo-Histidine Phosphotransfer Protein 3 in Oryza sativa

The two-component system is involved in several developmental events and different responses to the environment. Histidine-containing phosphotransfer proteins (HPs) play a critical role in transferring the phosphoryl group in the nucleus and regulating downstream effectors. Two authentic-HPs (OsAHPs) and three pseudo-HPs (OsPHPs) have been identified in rice. The conserved phosphorylation residue does not occur in OsPHPs, which are proposed as negative regulators in the cytokinin two-component system. One of the OsPHPs, OsPHP3, in rice is highly expressed at root caps. However, the roles of OsPHP3 have not been investigated in rice. We detected two major alternative splicing mRNAs of OsPHP3 and determined the expression in response to different environmental stimuli. The ratio of the two major alternative splicing OsPHP3 variants was significantly altered in response to a light signal and tissue specificity. Additionally, the results also indicated the positive regulation of auxin in the transcription of OsPHP3 in the root, and the ratio of the expression of the two major alternative splicing OsPHP3s was altered. OsPHP3 was also involved in auxin- and cytokinin-regulated lateral root development. Collectively, these results indicate a possible regulation of alternative splicing OsPHP3 isoforms by light and their roles in rice lateral root development.