Abstract
The rice (Oryza sativa L.) RISBZ1 bZIP and RPBF DOF proteins are transcriptional activators of rice seed storage protein (SSP) genes in vivo. To ascertain the functions of these trans-activators in seed development, knock-down (KD) transgenic rice plants with reduced RISBZ1 or RPBF accumulation level (KD-RISBZ1 and KD-RPBF). The accumulation of most SSPs changed little between individual KD mutants and wild type plants, whereas a double KD mutant (KD-RISBZ1/KD-RPBF) resulted in a significant reduction of most SSP gene expression and SSP accumulation. Starch and lipid accumulation levels were also decreased in these KD lines. KD-RPBF and KD-RISBZ1/KD-RPBF seeds exhibited multi-layered aleurone cells. These phenotypes suggest combinatorial interactions between RISBZ1 and RPBF play an essential role during grain filling. The functional redundancy and compensation between RISBZ1 and RPBF possibly account for weak effects on the SSP levels in single KD mutants, and help maintain various processes during seed development in rice. Physical interaction between RISBZ1 and RPBF may ensure that these processes are carried out properly.
