OsPHR1 And OsPHR2, Transcription Factors Involved In Signaling Of Phosphorus Starvation In Rice (Oryza Sativa L.)

The Arabidopsis gene AtPHR1 and the unicellular green alga (Chlamydomonas reinhardtii) gene PSR1 are members of the MYB-CC family, which are involved in the Pi-starvation signaling pathway. To investigate the function of the rice homologues in the regulation of the Pi-starvation signaling pathways, we isolated two rice homologues of AtPHR1, named OsPHR1 and OsPHR2, based on comparison of the sequence homology. Detailed analyses of OsPHR1 and OsPHR2, including the sequences features, expression patterns, and transgenic lines with overexpression and reduction of the genes indicate that:1. OsPHR1 and OsPHR2 are members of MYB-CC family with high homology in the conserved domains. Phylogenetic tree reveals that OsPHR1, OsPHR2 and AtPHR1 belong to the same subfamily, suggesting that the three genes are closely related in evolution. Alignment analysis indicates that both OsPHR1 and OsPHR2 have a single copy in the rice genome. Genomic DNA sequence analysis shows that OsPHR1 contains 8 exons and 7 introns, while OsPHR2 contains 9 exons and 8 introns. OsPHR1 and OsPHR2 are localized on chromosome 3 (Chr3: 120024-124948) and chromosome. 7 (Chr7: 24959-30561), respectively.2. RT-PCR analysis indicates that OsPHR1 and OsPHR2 showed a similar expression pattern in all tissues examined, while strongest in the leaves and roots. The two genes are relatively insensitive to Pi starvation.3. Using green fluenrecence protein (GFP) gene fused with either OsPHR1 or OsPHR2, OsPHR1 or OsPHR2 were found to be localized in the nucleus. In addition, the amino acid sequences near N terminus of these two proteins have kinase activity. These results suggest that OsPHR1 and OsPHR2 are transcription factors of MYB-CC family.4. Transgenic lines with reduced expression of OsPHR1 or OsPHR2 using RNAi display no apparent differences in phenotypes compared with the wild-type plants under both Pi-sufficient and Pi-starvation conditions. The repressed expression of Pi-starvation-inducible genes such as OsIPS1 and OsIPS2 was observed in rice plants reduced expression of OsPHR1 or OsPHR2. Overexpressed OsPHR1 or OsPHR2 results in the diminutive plants and reduction of Pi-signaling.The results indicate that OsPHR1 and OsPHR2 are two important components in the Pi-starvation signaling pathway in rice plants.