Department of Biology, Indiana University, Bloomington, IN.
Elemental Enzymes, Galt Industrial Boulevard, St. Louis, MO.
J Hered. 2020 Apr 2;111(2):216-226. doi: 10.1093/jhered/esaa003.
A goal of speciation genetics is to understand how the genetic components underlying interspecific reproductive barriers originate within species. Unilateral incompatibility (UI) is a postmating prezygotic barrier in which pollen rejection in the female reproductive tract (style) occurs in only one direction of an interspecific cross. Natural variation in the strength of UI has been observed among populations within species in the wild tomato clade. In some cases, molecular loci underlying self-incompatibility (SI) are associated with this variation in UI, but the mechanistic connection between these intra- and inter-specific pollen rejection behaviors is poorly understood in most instances. We generated an F2 population between SI and SC genotypes of a single species, Solanum pennellii, to examine the genetic basis of intraspecific variation in UI against other species, and to determine whether loci underlying SI are genetically associated with this variation. We found that F2 individuals vary in the rate at which UI rejection occurs. One large effect QTL detected for this trait co-localized with the SI-determining S-locus. Moreover, individuals that expressed S-RNase-the S-locus protein involved in SI pollen rejection-in their styles had much more rapid UI responses compared with those without S-RNase protein. Our analysis shows that intraspecific variation at mate choice loci-in this case at loci that prevent self-fertilization-can contribute to variation in the expression of interspecific isolation, including postmating prezygotic barriers. Understanding the nature of such intraspecific variation can provide insight into the accumulation of these barriers between diverging lineages.
物种形成遗传学的目标是了解种间生殖障碍的遗传组成在物种内部是如何产生的。单向不亲和性（UI）是一种交配后合子前的障碍，在这种障碍中，雌性生殖道（花柱）中的花粉排斥仅在种间杂交的一个方向上发生。在野生番茄类群中，已经在物种内的不同群体中观察到 UI 强度的自然变异。在某些情况下，自不亲和性（SI）的分子基因座与这种 UI 变异有关，但在大多数情况下，这些种内和种间花粉排斥行为之间的机制联系知之甚少。我们在单一物种 Solanum pennellii 的 SI 和 SC 基因型之间产生了一个 F2 群体，以研究 UI 对其他物种的种内变异的遗传基础，并确定是否存在与 SI 相关的基因座与这种变异有关。我们发现，F2 个体在 UI 排斥发生的速度上存在差异。一个针对该性状的大效应 QTL 与决定 SI 的 S 基因座共定位。此外，在花柱中表达 S-RNase 的个体（参与 SI 花粉排斥的 S 基因座蛋白）的 UI 反应速度比没有 S-RNase 蛋白的个体快得多。我们的分析表明，在配偶选择基因座（在这种情况下，防止自受精的基因座）中的种内变异可以导致种间隔离表达的变化，包括交配后合子前障碍。了解这种种内变异的性质可以为理解分歧谱系之间这些障碍的积累提供深入的了解。
