抗纹枯病水稻新种质TFX抗病QTL qSB3的精细定位与候选基因分析

Sheath blight (SB), caused by Rhizoctonia solani kühn, is one of the most serious global rice diseases. The resistance to rice SB is a typical polygenic quantitative trait. Over the past two decades, around 150 SB resistance quantitative trait loci (QTL) have been mapped. However, the parents used for QTL mapping are limited to a few varieties, such as Teqing, Jasmine85, and Tetep.To date, no genes have been identified for SB resistance, and few reports exist describing marker-assisted selection for SB resistance. In our previous study, A new rice line, TFX, showed relatively high level of resistance to SB in field experiment in many years. An F2 population derived from a cross between resistant variety TFX and a susceptible variety Lemont was produced for mapping SB resistance QTLs. Genome-wide analysis of the linkage map constructed from the F2 population showed that a major SB resistance QTL, designated qSB3, was detected on chromosomes 3 and the contribution rate to the total phenotypic variance reached to 23%. Furthermore, an advanced backcross population, which derived from resistant F3 lines,as donor,and susceptible parent Lemont,as the recipientan, was constructed,using advanced backcross and consecutive molecular marker-assisted selection strategy.In this study, Chromosome segment substitution Lines (CSSLs) will be constructed with the aim of fine-mapping of qSB3. The whole genome expression profiles between resistant near-isogenic line and Lemmont after inoculation with Rhizoctonia solani will be analyzed using RNA-seq technique. Combing the results of QTL mapping and RNA-seq, the candidate gene will be screened. Eventually, the sequence of the candidate gene in rice germplasm resources will be analyzed, their funtional mutational-sites and genes with potential beneficial value will be be explored using the association analysis. The results will accelerate the cloning of the quantitative genes, provide theoretical support for rice breeding using molecular methods and give important reference for studies of molecular mechanisms of resistance to rice SB.

纹枯病是世界性水稻三大病害之一，造成巨大的产量损失。“TFX”是项目组选育的抗纹枯病水稻新种质。申请人利用TFX与感病品种Lemont构建的F2群体及其衍生的F2:3家系在3号染色体定位到1个抗纹枯病主效QTL qSB3，贡献率21%。进而获得了qSB3区间为杂合且具有Lemont遗传背景的2个抗病F3单株，结合基因组前景背景选择及抗性鉴定，构建了抗病F3的高代回交群体。本研究拟在此基础上进一步构建高密度依次覆盖qSB3区间的染色体片段代换系精细定位qSB3；利用转录组测序分析纹枯病菌胁迫条件下Lemont及其抗病近等基因系NIL-qSB3TT差异表达基因和SNP；将精细定位区间与差异基因信息整合，筛选抗病候选基因；利用关联分析方法确定候选基因功能性突变位点，发掘具有潜在利用价值的有利等位变异；为水稻抗纹枯病分子机理研究提供重要参考，为利用分子育种途径提高纹枯病抗性提供理论依据。

纹枯病是世界性水稻三大病害之一，造成巨大的产量损失。本项目前期利用TFX与感病品种构建的F2群体在3号染色体定位到1个抗纹枯病主效QTL qSB3，贡献率21%。进而获得了qSB3区间为杂合且具有感病亲本遗传背景的抗病F3单株，结合基因组前景背景选择及抗性鉴定，构建了高密度依次覆盖qSB3区间的染色体片段代换系，将qSB3定位于N8与N10之间约137kb的区间内，该区间内预测了20个候选基因。利用转录组测序分析接种和不接种纹枯病菌条件下抗病近等基因系及感病亲本差异表达基因，发现在精细定位区间内只有2个候选基因LOC_Os03g24680和LOC_Os03g24690在侵染前后及抗感品种中的表达量均差异显著，这2个基因是新的抗病基因，均编码萜类合酶，而萜类合酶可能是控制植保素和化感物质等防御化合物合成的一个很重要的调节因子。利用候选基因关联分析方法发现，LOC_Os03g24690编码区第534位碱基由C突变为A，氨基酸由丙氨酸变为丝氨酸，抗性可显著提高，位点贡献率为33.4%，120份水稻核心种质中只有3份在该位点发生了突变，具有潜在的应用价值。项目的研究结果可以为深入了解水稻抗纹枯病分子机制提供重要参考；为水稻抗纹枯病的遗传改良提供基因资源和理论依据。项目资助发表论文5篇，其中SCI 1篇，获江西省科技进步一等奖1项。培养毕业硕士生1名，本科生3名。