Genetic Analysis And Fine Mapping Of Bn1(brittle Node 1) Inrice(oryza Sativa L.)

Cell wall which is localized at the outermost layer of palnt cell is mainly composed of cellulose, and is a specific structure which is important to maintain the shape of plant cell. Brittle mutant is the ideal material to study rice cell wall. In order to explore the molecular mechanism and genetic control of rice, we identified a brittle mutant which was mutated by EMS from the M2 generation of a japonica cultivar Wuyunjing 7(WYJ7). The mutant showed brittleness in node and no obvious difference was observed in other part for brittleness, thus we designated it as bn1(brittle node 1).Genetic analysis indicated that bn1 is controlled by a single-recessive gene. Biochemical analysis showed that cellulose content was decreased in the node from 359.2 ug/mg in the wild type to 343.3 ug/mg in the bn1, however no significant difference was observed for cellulose content in the internode. Further more, the composition of monosaccharide was altered in the node of bn1. Among which, the glucose content was increased from 36.48 ug/mg in the wild type to 45.87 ug/mg in bn1, thus, we predicated that BN1 might involve in the biosynthesis of cellulose in node. In bn1, the plant height, panicle length and number of primary branches were decreased. But the number of secondary branches was largely increased, which lead to the increase of spikes per panicle and seed density. Compared with wild type, the grain length, width and 1000-grain weight were decreased. In order to study the function of BN1, we fine-mapped it using map based cloning strategy, 1, 376 mutants were selected from a F2 population of about 6, 000 plants. BN1 was primarily narrowed down to 9.2 c M region of chromosome 2 and finally fine-mapped to a 233.8 kb region. For transcriptome analysis, the number of genes down or up-regulated was larger for those related to the organic, the primary and the cellular metabolic processes; this result suggests that the mutation of BN1 might affect the cellular metabolic process. In addition, q RT-PCR was used to analyze the expression of part of genes related to the biosynthesis of cell wall. The result showed that genes including BC1, BC3, Os Ces A4, Os Ces A7 and BC6/Os Ces A9 which involved in the thicking of cell wall were all significantly down-regulated.The results above suggest that the mutation in BN1 might lead to the disruption of cellulose biosynthesis and decrease of cellulose content in rice node, which further affects the thickness of cell wall and induces the brittleness of node. This study has laid a foundation for cloning and exploring the genetic control of BN1.