小麦矮秆基因Rht12的精细定位和候选基因预测

The introduction of dwarf gene Rht1 and Rht2 into wheat was significantly increased grain yield, and resulted in the ‘Green Revolution’. However, Rht1 and Rht2 reduced coleoptile length and seedling vigour which may reduce crop performance in some unfavorable environments. So, opportunities exist for replacing Rht1 and Rht2 in wheat with alternative dwarfing genes. Rht12, a GA-responsive dwarfing gene, can reduce plant height without compromising early plant growth. Additionally, Rht12 can significantly increase the number of effective tillers, grain number per spike, and achieve higher harvest index. But, the mechanism of dwarf caused by Rht12 was not clear, and there was also no co-segregated molecular marker can be used in marker assisted selection in wheat breeding. This study will develop new SNP/InDel markers closely linked with Rht12 to fine mapping the Rht12 locus using the F2 population developed by the cross of Chinese cultivar Jinmai47 and Australian introduced Karcagi (with Rht12), by fully exploring the information on wheat 5AL survey sequences and wheat SNP array. Additionally, the candidate genes in the target region will be analyzed using bioinformatics methods to provide the foundation for its cloning and function characterization. The expected results of this study will greatly promote the proper utilization of Rht12 in wheat breeding and the mechanism analysis of dwarfing caused by Rht12, and help to understand the molecular mechanism underlying the construction of plant architecture and yield production, and finally provide new sight to dwarf breeding in wheat.

小麦矮秆基因Rht1和Rht2的应用引发了粮食生产的 “绿色革命”。然而，Rht1、Rht2会缩短胚芽鞘长度，影响苗期活力。因此，需挖掘应用新的矮源。小麦矮秆基因Rht12为赤霉素敏感型，在降低株高的同时不影响胚芽鞘长度和苗期活力，且可显著提高有效穗数、穗粒数和收获系数，应用潜力极大。但是，Rht12的致矮机理目前还不清楚，也没有可用于辅助选择的共分离分子标记。本项目以中国小麦品种晋麦47和引自澳大利亚的小麦材料Karcagi（含Rht12）的F2分离群体为材料，以小麦5AL染色体的探查序列和SNP芯片信息为基础，开发新的SNP/InDel标记，精细定位Rht12，以发掘实用分子标记；并利用生物信息学方法分析目标区间内的候选基因，为后续克隆奠定基础。本研究将极大促进Rht12的合理应用和致矮机理研究，并有助于揭示赤霉素等植物激素影响作物株型及产量形成的分子机制，为小麦矮化育种提供新的思路。

小麦矮秆基因Rht1和Rht2的应用引发了农业生产的 “绿色革命”。然而，Rht1、Rht2会缩短胚芽鞘长度，影响苗期活力。因此，需挖掘应用新的矮源。小麦矮秆基因Rht12在降低株高的同时不影响胚芽鞘长度和苗期活力，且可显著提高有效穗数、穗粒数和收获系数，应用潜力极大。本研究首先利用中国小麦品种晋麦47和引自澳大利亚的小麦材料Karcagi（含Rht12）杂交，构建F2定位群体。以小麦SNP芯片数据及RNA-seq发现的高、矮材料间的差异SNP，开发KASP标记，最终将Rht12定位到5AL染色体末端4.6Mb的区间，距标记5A-57981850、5A-97680000和5A-13852470 0.4cM，这些标记可清晰的区分Rht12矮秆系与高秆系及其他普通小麦材料，可作为Rht12分子标记辅助选择育种的工具。在该区间内，共预测到76个基因，功能分析暂未发现直接与赤霉素代谢或茎节发育相关的基因。同时，对Rht12高、矮系两个时期的穗下茎（伸长初期、伸长中期）进行了RNA-seq分析，差异表达基因富集分析发现，所有差异表达基因都富集在生物过程和分子功能子类别中，且都主要富集在钾离子运输、细胞形态发生、氧化还原酶活性、L-半胱氨酸/半胱氨酸进程和NAD结合等子类中。KEGG富集分析显示这些差异表达基因主要富集在内质网蛋白加工、糖酵解/糖异生及其他代谢过程。同时，与高秆系相比，矮秆系中有5个基因在两个时期都上调表达、24个基因都下调表达，初步推测这29个基因可能与小麦穗下茎的伸长有关。另外，有两个差异表达基因接近Rht12定位候选区间，其富集到蛋白泛素化和小分子代谢进程，这两个基因可作为Rht12或小麦茎节发育的候选基因。另外，为了创制Rht12新种质，项目组将促进早开花的Ppd-D1a引入矮秆系，发现Ppd-D1a可打破Rht12晚开花的不利效应，促进矮秆系提前开花，并显著提高矮秆系的千粒重、单株产量和收获系数。目前，已选育出生育期适宜、综合农艺性状优良的Rht12矮秆系，为小麦矮化、抗倒伏育种提供了新的资源。本研究在开发Rht12实用分子标记的基础上，对Rht12候选基因进行了初步分析，并创制了一批矮秆新种质，为Rht12致矮机理研究和育种应用奠定了基础。