v301, a new allele of BRITTLE CULM 12, and its regulation of the early senescence of the leaf blade in rice

The leaf is the main site for plant photosynthesis and an important component of the maximally efficient plant architecture of rice. Early senescence of leaves affects directly both the yield and the quality of crops. Accordingly, it is very important to explore the mechanism of premature senescence of leaves for rice breeding to promote high photosynthetic efficiency. A mutant v301 with shorter plant height and wider grains increased brittleness in the main veins of leaves, and premature ageing at the leaf tip was obtained by treatment with ethyl methanesulfonate (EMS). Fine gene mapping and identification of candidate genes indicated v301 as a new BC12 allele mutant. Under field planting conditions, there was no significant difference in leaf colour between the wild type (WT) and v301 and before the booting stage, but yellowing and premature senescence appeared subsequently at the leaf tip in v301. Further analysis revealed that the chlorophyll content and net photosynthetic rate in the leaf tip of v301 are significantly lower than those of the WT, while both the content of photosynthetic pigments and the net photosynthetic rate in the leaf base are significantly higher. qRT-PCR analysis showed that in addition to the obvious reduction in gene expression related to chlorophyll synthesis and chloroplast development, the expression of ageing retarding genes expression level of OsCatB, OsETR2, OsAkaGal, JARIDIC, OsAPX1 and OsAPX2 was decreased, whereas SGR, OsL85 and OsH36 were significantly increased. At the same time, the gibberellin related genes GA2ox1, GA3ox2 were significantly reduced, and KO2 showed an extremely significant decline in the leaf tip. The contents of WT and v301 gibberellin GA3 were determined by liquid chromatography, and a significant decrease in gibberellin content was found in mutant v301. The activities of SOD, CAT and POD in the senescent leaf tips of v301 are significantly lower than in WT, whereas the activities of H2O2 and hydroxyl radicals are significantly higher. It is suggested that BC12 might affect the premature senescence of leaves via the peroxidation system.