Department of Biology, McGill University, Montreal, QC, H3A 1B1, Canada.
New Phytol. 2017 Jan;213(1):430-439. doi: 10.1111/nph.14109. Epub 2016 Jul 22.
Self-incompatibility (SI) promotes outcrossing, but transitions to self-compatibility (SC) are frequent. Population genetic theory describing the breakdown of SI to SC suggests that, under most conditions, populations should be composed of either SI or SC individuals. Under a narrow range of conditions, theory suggests that SI may persist alongside reduced expression of SI (pseudo-SI, PSI) in mixed-mating populations. We studied genetic variation for PSI segregating in four SI populations of Leavenworthia alabamica by measurement of the heritability of pollen tube number after self-pollination. We tested for the role of the S-locus in this variation by sequencing seven S-alleles from plants with high pseudo-SC (PSC) and testing for the co-segregation of these alleles with PSC. We found a continuous distribution of PSC in all populations and 90% of plants exhibited PSC. The heritability ranged from 0.39 to 0.57. All seven S-alleles from plants with high PSC exhibited trans-specific polymorphism, and no stop codons were observed within the c. 600-bp region sequenced. One of these S-alleles was directly associated with the inheritance of PSC. We conclude that heritable variation in PSC is largely a result of genetic variation in the signaling cascade downstream of the S-locus reaction, together with the presence of one leaky S-allele.
自交不亲和性（SI）促进异交，但自交亲和性（SC）的转变很常见。描述 SI 向 SC 打破的种群遗传理论表明，在大多数情况下，种群应该由 SI 或 SC 个体组成。在狭窄的条件范围内，理论表明 SI 可能与混合交配种群中 SI 表达的降低（伪 SI，PSI）共存。我们通过测量自授粉后花粉管数量的遗传力，研究了 Leavenworthia alabamica 的四个 SI 种群中 PSI 分离的遗传变异。我们通过从具有高伪 SC（PSC）的植物中测序七个 S 等位基因来测试 S 基因座在这种变异中的作用，并测试这些等位基因与 PSC 的共分离。我们在所有种群中发现了连续分布的 PSC，90%的植物表现出 PSC。遗传力范围从 0.39 到 0.57。来自具有高 PSC 的植物的七个 S 等位基因均表现出跨种多态性，并且在所测序的约 600bp 区域内未观察到终止密码子。这些 S 等位基因之一与 PSC 的遗传直接相关。我们得出结论，PSC 的可遗传变异主要是 S 基因座反应下游信号级联的遗传变异以及一个渗漏 S 等位基因的结果。
