Light Signals Mediated By Phytochrome B Affect The Reponses Of Abscisic Acid In Rice

Rice is an important food crops throughout the world. Rice production suffered a lot from diverse abiotic and biotic stresses. Thus it is very important to explore the mechanisms of stress responses and then cultivate high-resistance and high-yield rice varieties. It has been well known that abscisic acid (ABA) is a key hormone involved in stress responses, especially in abiotic stress response, in plants. Interaction between phytochrome-mediated light signaling and ABA signaling pathway has been reported in Arabidopsis. However, whether similar interaction exists in rice still remains elusive. In order to explore this problem, in this study, we have analyzed effects of phytocrome B (phyB)-mediated light signals on ABA metabolism and ABA response pathways using phyB-deficiency mutants and wild type (WT). We also performed Genechip analysis and chose candidate genes which are probably involved in both light signaling and ABA pathway. To further explore roles of these genes in rice growth, we analyzed the expression patterns of some candidate genes and produced overexpression transgenic rice lines. The main results obtained in this study are as followed.(1) It was observed that transcript levels of ABA biosynthetic genes (including OsNCED1and OsNCED3) were higher in the phyB mutant relative to those in WT, whereas transcript level of ABA deactivating genes (including OsABA8OX1, OsABA8OX2and OsABA8OX3) were lower in the phyB mutant than in WT, which probably contributed to the relatively high ABA content in the phyB mutant. These results suggest that phyB-mediated light signal negatively regulate ABA accumulation in rice.(2) ABA treatment inhibited germination of rice seeds grown either in the dark or under light. However, inhibitory effects of ABA treatment on seed germination were more obvious in phyB mutants than in WT when seeds were grown under light conditions, suggesting that phyB-mediated light signals attenuated the inhibitory effects triggered by ABA. Meantime, we compared the expression patterns of genes related to seed germination in WT and the phyB mutant grown in the medium with or without ABA. It was deduced that these genes is unlikely to contribute for the promotive effects of phyB-mediated light signals on seed germination. (3) ABA treatment inhibited growth of both above-ground part and seminal root in rice seedlings. phyB-mediated light signals did not affect the ABA-induced inhibition of above-ground part growth, but negatively regulate the inhibition of root growth. These results suggest that phyB-mediated light signal negatively regulate ABA responses in rice.(4) We analyzed the expression patterns and function of candidate genes which were screened by Genechip using quantitive real-time PCR. We observed that transcript levels of those genes were affected by ABA and phyB-mediated light signal, suggesting that phyB-mediated light signal is likely to regulate the ABA responses by influencing the expression of these genes. By overexpressing an S receptor-like protein kinase gene (OsS-RE, AK068992), we found that this gene obviously influences rice leaf length and leaf width, as well as the salt tolerance and fertility in rice.For the first time, our findings reveal the effects of phyB-mediated light signals on ABA pathway, which lays the foundation for dissecting the molecular mechanism of coordinated regulation of rice development by light and ABA in rice. Meantime, our study also accumulates some materials for cultivating high-yield and high resistance rice.