Rice NPH1 homologues, OsNPH1a and OsNPH1b, are differently photoregulated

The members of nonphototropic hypocotyl 1 (NPH1) family of genes in plants are considered to be the blue-light photoreceptors for phototropism. We isolated and characterized two NPH1 homologues from rice named as OsNPH1a and OsNPH1b. The predicted proteins of both OsNPH1 genes include LOV (LOV1 and LOV2) and protein kinase domains which are typically conserved regions in all the members of NPH1 family. Comparison of OsNPH1 apoproteins with those from other plant species revealed a close homology of OsNPHla with Arabidopsis, maize and oat NPH1, while the OsNPH1b appeared to be more closer to the recently found Arabidopsis NPL1. These structural homologies indicate that NPH1 homologues can be grouped into two classes namely "NPH1 type" and "NPL1 type". Northern blot analysis showed that OsNPH1a was strongly expressed in coleoptiles, whereas OsNPH1b was highly expressed in leaves of dark-grown rice seedlings. When the dark-grown seedlings were transferred to the continuous white light, the abundance of the OsNPH1a transcript in coleoptiles rapidly declined to the minimum levels, whereas the OsNPH1b transcript level in leaves gradually increased. These results lead us to conclude that expression of OsNPH1a and OsNPH1b is differently photoregulated in different tissues of rice seedlings.