OsHAP3 genes regulate chloroplast biogenesis in rice.

We have isolated three genes that potentially encode a HAP3/nuclear factor-YB (NF-YB)/CCAAT binding factor-A (CBF-A) subunit of a CCAAT-box binding complex in rice (Oryza sativa), and named them OsHAP3A, OsHAP3B and OsHAP3C. These genes were expressed in various organs including leaves. In the transgenic rice plants with antisense or RNAi construct of OsHAP3A, reduced expression of not only OsHAP3A but also OsHAP3B and OsHAP3C was observed. These plants had pale green leaves, in which the amount of chlorophyll was reduced and chloroplasts were degenerated. Lamella was not well developed and accumulation of starch was not detected. The degenerated chloroplast formation was accompanied by reduced expression of nuclear-encoded photosynthesis genes such as RBCS and CAB, while expression of chloroplast-encoded genes was not affected or rather increased. These results suggest that one or more OsHAP3 genes regulate the expression of nuclear-encoded chloroplast-targeted genes and normal development of chloroplasts.