油菜素内酯调控水稻株型与粒型的分子机制

Rice architecture and grain size is significant for enhancing rice yield. Recently, several genes related rice architecture and grain size have been cloned, but the molecular regulatory networks remain largely unknown. In our preliminary study, we identified asg2 mutant with reduced plant height, lamina joint inclination and grain length from the mutant library generated from the core parent of heavy panicle hybrid rice--Shuhui498. Genetic and mapping analysis indicated that the phenotype of sg2 was controlled by two recessive genes which were msp and osserk1, and the single mutants harboring mutation in MSP and OsSERK1 were named 07sg2 and 08sg2, respectively. The plant height and grain length of 07sg2 and 08sg2 was between WT and sg2, moreover, 07sg2, 08sg2 and sg2 were less sensitive to BRs. These suggested that two candidates regulated plant height and grain size through brassinosteroid signal pathway, and had some relationship each other. In this project, we will take use of the sg2, 07sg2, 08sg2, osbri1 mutants to study the molecular mechanism on the development of plant architecture and grain size of MSP，OsSERK1 and OsBRI1，and their relationship from the aspects of brassniosteroid signal pathway, genetics, cytology and molecular biology. Our result will provide a base for revealing the molecular regulatory networks of rice architecture and grain size，and provide a theoretical basis for further seeking elite allelic genes and molecular design breeding related rice architecture and grain size.

水稻株型和粒型对提高水稻产量具有重要意义。虽然近年克隆了多个相关基因，但其分子调控网络还不清楚。我们前期从重穗型杂交稻骨干亲本蜀恢498突变体库中鉴定了一份株高降低，叶夹角变小和粒长变短材料sg2。遗传和定位分析表明sg2受msp和osserk1两对隐性基因控制，分离后的单突07sg2和08sg2株高与粒长均介于WT与双突之间，且单突，双突对BL表现顿感，表明两候选基因可能通过BR信号途径调控株高和粒型，且二者具有一定的相互作用。本项目拟在已有研究基础上，利用sg2, 07sg2，08sg2和osbri1突变体从BR信号途径出发，在遗传，细胞学，分子生物学等方面深入研究MSP，OsSERK1与OsBRI1调控水稻株型和粒型发育的分子机制，以及他们的相互关系，为全面解析水稻株型和籽粒发育的分子调控网络奠定基础，进一步发掘优良等位基因，为水稻株型和籽粒相关的分子设计育种提供基因资源和理论依据。

水稻是世界上最重要的粮食作物之一，是全球一半以上人口的主食。粒型不仅是决定水稻产量的一个重要因素，而且还会影响稻米外观品质。近年来，很多粒型相关基因已经被克隆，但是这些基因的调控机制还并不是很清楚。我们在重穗型杂交稻骨干亲本蜀恢498 (R498)的EMS诱变突变体库中鉴定到一个小粒突变体short grain 2 (sg2)，sg2突变体主要表现为株高降低，穗长，粒长变短。遗传分析表明sg2表型受两对隐性基因控制。结合回交分离群体和Mutmap测序定位方法：将sg2定位在第7和第8号染色体上。对候选基因进行共分离及转基因验证，将sg2的候选基因确定为第7号染色体上的LOC_Os07g37270 (Motile Sperm Protein, MSP)和第8号染色体上的LOC_Os08g07760 (OsBAK1) 。同时利用以上两个基因SNP开发的功能标记在群体中分离得到只含有第7号与第8号染色体单突变位点的材料，分别命名为07sg2和 08sg2。.07sg2，08sg2均表现为株高降低，粒长和穗子变短。细胞学及定量分析发现，07SG2及08SG2均是通过调控细胞周期相关基因表达，影响细胞数量来调控粒长。对07SG2及08SG2进行序列分析发现，这两个基因在不同植物中都是比较保守的，而且07sg2和08sg2突变位点都是发生在各自结构域非常保守的位点，最终产生明显的表型。对07sg2进行转录组分析发现，ABA信号途径相关基因表达量有显著上调，而且ABA含量在07sg2中显著增加，预示着07SG2可能通过ABA途径调控粒型；08SG2/OsBAK1编码一个BR信号受体BRI1的激酶，参与BR信号转导，系列BR敏感性测试实验发现，08sg2对BR敏感性降低，而BR相关基因定量分析发现，正调控BR信号的BU1表达显著下调，而BR生物合成相关基因OsDWARF, D2, OsDWARF4表达显著上调，为BR信号途径调控粒型提供新的直接证据。08SG2相互作用蛋白已鉴定完成，处于转基因验证表型过程。将07sg2，08sg2，NIL-GS3进行聚合分析粒长发现，这三个基因可能是通过独立的途径调控粒长。07SG2/MSP，08SG2/OsBAK1的研究为全面揭示水稻株型和籽粒发育的分子调控网络奠定基础，为调控水稻株型和籽粒大小提高水稻产量提供材料和理论依据。

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