Myosin XI is associated with fitness and adaptation to aridity in wild pearl millet

Phenotypic changes in plants can be observed along many environmental gradients and are determined by both environmental and genetic factors. The identification of alleles associated with phenotypic variations is a rapidly developing area of research. We studied the genetic basis of phenotypic variations in 11 populations of wild pearl millet (Pennisetum glaucum) on two North-South aridity gradients, one in Niger and one in Mali. Most of the 11 phenotypic traits assessed in a common garden experiment varied between the populations studied. Moreover, the size of the inflorescence, the number of flowers and aboveground dry mass co-varied positively with a decrease in rainfall. To decipher the genetic basis of these phenotypes, we used an association mapping strategy with a mixed model. We found two SNPs on the same myosin XI contig significantly associated with variations in the average number of flowers. Both the allele frequency of the two SNPs and the average number of flowers co-varied with the rainfall gradient on the two gradients. Interestingly, this gene was also a target of selection during domestication. The Myosin XI gene is thus a good candidate for fitness-related adaptation in wild populations.

植物的表型变化可沿多种环境梯度被观测到，其由环境与遗传因素共同决定。鉴定与表型变异相关的等位基因，是当前快速发展的研究热点领域。本研究以分布于尼日尔和马里的两条南北走向干旱梯度上的11个野生珍珠粟（Pennisetum glaucum）种群为材料，探究其表型变异的遗传基础。在同质园试验中测定的11项表型性状中，多数供试性状在种群间存在显著差异。此外，花序大小、小花数目及地上干物质重随降雨量减少呈正相关变化趋势。为解析上述表型的遗传基础，本研究采用混合模型关联作图策略开展分析。本研究在同一个肌球蛋白XI（myosin XI）重叠群上，发现了两个与平均小花数目变异显著相关的单核苷酸多态性位点（Single Nucleotide Polymorphism，SNP）。这两个SNP的等位基因频率与平均小花数目，均随两条干旱梯度的降雨量梯度呈现协同变化。值得注意的是，该基因同时也是作物驯化过程中受选择的靶标基因。因此，肌球蛋白XI基因可作为野生种群中与适合度相关适应性进化的优质候选基因。