水稻适应旱直播幼苗形态特性的关联定位与候选基因研究

Irrigation water could be largely saved in rice production after application of drought resistant varieties and mechanized dry direct sowing method. Most present varieties were developed for transplanting or wet direct sowing system without optimizing their characteristics for dry direct sowing. Elongation of both mesocotyl and coleoptile increases the speed and uniformity of seedling emergence of deep-sown seeds that is the basis of competition against weeds and high-yielding population structure. Mesocotyl elongated at the dark that stopped after exposure to light. This characteristics support the self-adaptation of seedlings to sowing depth. This study take comprehensive considerations on sowing depth, final lengths of mesocotyl and coleoptile (and their ratio) to propose a optimized pattern of early seedling morphological characteristics. The influence of low soil water content and low temperature are analyzed to estimate compensation of seedling characteristics. Using natural varied populations like mini- core-collection of Chinese rice germplasm, drought resistant varieties and collection of global rice germplasm and ready-to-use SNP genotypic data, association mapping will be conducted for mesocotyl length, coleoptile length, their ratio, seedling emergence rate and quality after properly deep-sowing. Using backcross progenies and derived segregation populations with elite restorers of water-saving and drought-resistant rice (WDR) as the recurrent parents, QTL fine mapping and development of new WDR materials adapting to dry direct sowing will be conducted. Analysis of differential gene expression during the procedure of light inhibition to mesocotyl elongation will be used to accelerate the identification and cloing of candidate genes. Researches on functions of target genes and the regulation mechanism will be conducted in this study.

采用抗旱品种和机械化旱直播栽培体系可使稻作大幅度节水，现有品种多按移栽或水直播条件选育，未按旱直播优化特性。幼苗通过中胚轴和胚芽鞘的伸长提高出苗速度和整齐度，是对杂草竞争力和高产群体的基础。中胚轴黑暗伸长，见光后停止，形成幼苗对播深自适应机制。本研究拟综合考虑播种深度、中胚轴长度和胚芽鞘长度及比例，提出适应旱直播的早期幼苗形态性状的优化模式，分析土壤水分不足和低温影响以及补偿性状参数。利用我国水稻微核心种质、抗旱水稻品种和全球水稻品种等自然变异群体，已获得全基因组SNP基因型数据，拟开展中胚轴和胚芽鞘长度及其比例、适度深播条件下出苗率和秧苗素质等性状的关联定位。以节水抗旱稻优良恢复系为受体亲本，利用回交后代及其次级分离群体进行QTL精细定位，同时转育适应旱直播条件的节水抗旱稻新种质。采用中胚轴延长受光抑制过程中差异表达基因分析等手段加快候选基因鉴定和克隆，开展目标基因的功能和调控机制研究。

课题前期已完成我国微核心种质和抗旱亲本群体的表型鉴定，执行期间又完成358份我国水旱稻地方种和292份全球水稻多样性种质等2套群体的中胚轴延长特性表型鉴定，3套群体合计规模达到920份，鉴定出“Rikutonorin21”、“云陆8号”、“扎西马”、“Dular”、“毫刚”、“蔚县大黑芒”、“深水稻”、“山齐头谷”、“鲁达谷”、“秦皇岛大红芒”、“Phudugey”、“Kasalath”、“CA902B21”、“Surjamkuhi”、“Djimoron”等15份优异种质的中胚轴延长能力居各群体前5位。地方种、旱稻品种资源中有较高比例的材料保留了中胚轴延长特性，兼具抗旱性和中胚轴延长能力的种质资源在易旱地区直播稻育种计划中有重要应用价值。.基于上述鉴定所获表型数据以及重测序或芯片检测SNP基因型数据，完成3套群体中胚轴延长特性的全基因组关联分析，结合已有文献报道结果，筛选出水稻第1、3、4、5、6、9、10号染色体上共10个重要QTL区间，设计的SNP分子标记在亲本以及回交后代株系之间通过HRM曲线实现分型。同时还开展了胚芽鞘长度鉴定和GWAS定位。.光照能完全阻断水稻中胚轴延长，设置20分、60分和360分钟光照处理，收集受光前后中胚轴组织多组对比样品，监测转录组和内源植物激素的动态变化，发现974个差异表达基因，基因功能和信号通路富集分析结果明显指向植物激素信号和代谢通路，与植物激素含量变化情况吻合，再次明确IAA和GA3正向调控中胚轴延长，也发现JA起负向调控作用。.综合运用关联分析和连锁定位重复共定位结果、分离群体混池测序分析、基因功能注释相关性、长短中胚轴品种组间基因表达特征等参考依据，克隆十余个候选基因并开展转录调控原件等分析，其中OsMsc5、OsMsc8和OsSub1C等3个候选基因的转基因材料观察到相应的中胚轴延长表型，后续基因功能和调控机制研究尚在进行之中。水稻中胚轴延长相关候选基因、分子标记及其应用，获得了2项国家发明专利授权。.将中胚轴延长特性回交导入“旱恢3号”，后代稳定选系在8-10cm深播条件下出苗快1-2天，齐苗率和后期幼苗生长量显著好于受体亲本。