青藏扁蓿豆(Medicago archiducis-nicolai)为苜蓿属（Medicago）阔荚苜蓿组(Section Platycarpae)的核心种之一，属古北极第三纪植物区系残遗种(remnant)，广布于青藏高原及其毗邻地区，对海拔差异导致的局部异质性极端生境具有极强的适应性，是研究青藏高原极端环境植物适应机制的理想物种。本项目拟利用已经获得的低温胁迫转录组测序信息，开发青藏扁蓿豆其逆境胁迫和发育相关基因的EST-SSR标记；在中性遗传标记群体遗传多样性和遗传结构分析基础上，鉴定环境选择相关EST-SSR离群位点(outlier loci)，分析气候因子与等位基因频率的关联性，筛选与极端环境适应相关的基因组区段或基因；进行部分候选基因的生物学功能解释和实验验证。希望通过上述研究工作，部分解释青藏扁蓿豆适应青藏高原极端环境的分子机制，也为栽培苜蓿抗寒性定向改良提供参考信息。

Medicago archiducis-nicolai Sirjaev is an allogamous diploid perennial species and one of the cohesive core in the section Platycarpea of the genus Medicago. It appears to be one of remnants of an ancient Arcto-Tertiary complex of flora forebearing many new genera including Medicago and Trigonelle. It has been found that M. arciducis-nicolai is widely distributed in the Qinghai-Tibet Plateau (QTP) and its adjacent areas as the only species in the genus Medicago that can survives the extremely harsh environments mainly caused by altitudinal difference in the QTP, M. archiducis-nicolai is an ideal species for elucidating of the mechanisms of plant adaptation to the extreme environment in the QTP. In an attempt to dissecting the molecular genetic mechanism of M. archiducis-nicolai adaptation to the extremely harsh environments in the QTP and casting light on improvement for abiotic stress tolerance in the cultivated species of the genus Medicago, especially for winter hardiness, this study plans to develop abiotic stress- and development-related EST-SSR markers based on our now available RNA-Seq data of cold treated M. archiducis-nicolai, and to search for molecular signatures of divergent selection in M. archiducis-nicolai natural populations by identification of EST-SSR outlier loci associated with the environmental factors. EST-SSR alleles associated with climatic variables will be investigated to reveal genetic polymorphisms contributing to local adaptation on the QTP. Moreover, the roles of candidate genes revealed by potential divergent selected EST-SSR loci will be further verified taking advantages of known knowledge and validated by experiments.