Brassinosteroid signaling may regulate the germination of axillary buds in ratoon rice

BACKGROUND: Rice ratooning has traditionally been an important component of the rice cropping system in China. However, compared with the rice of the first harvest, few studies on factors effecting ratoon rice yield have been conducted. Because ratoon rice is a one-season rice cultivated using axillary buds that germinate on rice stakes and generate panicles after the first crop’s harvest, its production is mainly affected by the growth of axillary buds. The objectives of this study were to evaluate the sprouting mechanism of axillary buds to improve the ratoon rice yield. RESULTS: First, we observed the differentiation and growth dynamics of axillary buds at different nodes of Shanyou 63, and found that they differentiated from bottom to top before the heading of the mother stem, and that they developed very slowly. After heading they differentiated from top to bottom, and the ones on the top, especially the top 2nd node, developed much faster than those at the other nodes. The average length and dry weight of the axillary buds were significantly greater than those at other nodes by the yellow ripe stage, and they differentiated into pistils and stamens by 6 d after the yellow ripe stage. The morphology of vegetative organs from regenerated tillers of Shanyou 63 also suggested the superior growth of the upper buds, which was regulated by hormones, in ratoon rice. Furthermore, a comprehensive proteome map of the rice axillary buds at the top 2nd node before and after the yellow ripe stage was established, and some proteins involved in steroid biosynthesis were significantly increased. Of these, four took part in brassinosteroid (BR) biosynthesis. Thus, BR signaling may play a role in the germination of axillary buds of ratoon rice. CONCLUSIONS: The data provide insights into the molecular mechanisms underlying BR signaling, and may allow researchers to explore further the biological functions of endogenous BRs in the germination of axillary buds of ratoon rice.