Rice NPH1 homologues, OsNPN1a and OsNPN1b, 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 iso lated 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 a ll the members of NPH1 family. Comparison of OsNPH1 apoproteins with those from other plant species revealed a close homology of OsNPH1a with Arabidop sis, maize and oat NPH1, while the OsNPH1b appeared to be more closer to th e recently found Arabidopsis NPL1, These structural homologies indicate tha t NPH1 homologues can be grouped into two classes namely "NPH1 type" and "N PL1 type". Northern blot analysis showed that OsNPH1a was strongly expresse d in coleoptiles, whereas OsNPH1b was highly expressed in leaves of dark-gr own rice seedlings. When the dark-grown seedlings were transferred to the c ontinuous white Light, the abundance of the OsNPH1a transcript in coleoptil es rapidly declined to the minimum levels, whereas the OsNPH1b transcript l evel in leaves gradually increased. These results lead us to conclude that expression of OsNPH1a and OsNPH1b is differently photoregulated in differen t tissues of rice seedlings.