植物自交繁殖方式的演化

植物的自花受精会造成自交退化，即自交所产后代适应性降低。但正如达尔文所预测的，当授粉者或交配对象稀少时，自交可能会受到青睐。

防止自交的主要机制是自交不亲和性识别体系，它由雄性和雌性特异性基因及修饰基因组成。

据预测，由花粉和种子传播的雄性基因的突变相对于雌性基因的突变体会居支配地位。这个预测被对从欧洲各地获得的以自交为主的拟南芥的DNA序列所做比较证实。在95%的这些序列中，在雄性特异性基因(SCR)或一个衍生物中有一个破坏性的213-碱基对倒位。自交不亲和性通过将这种重新排列恢复到其原始取向而得以恢复。

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Evolution of self-compatibility in Arabidopsis by a mutation in the male
specificity gene
Takashi Tsuchimatsu,Keita Suwabe,Rie Shimizu-Inatsugi,Sachiyo Isokawa,Pavlos Pavlidis,
Thomas Stdler,Go Suzuki,Seiji Takayama,Masao Watanabe& Kentaro K. Shimizu

【Abstract】Ever since Darwin’s pioneering research, the evolution of self-fertilisation (selfing) has been regarded as one of the most prevalent evolutionary transitions in flowering plants. A major mechanism to prevent selfing is the self-incompatibility (SI) recognition system, which consists of male and female specificity genes at the S-locus and SI modifier genes. Under conditions that favour selfing, mutations disabling the male recognition component are predicted to enjoy a relative advantage over those disabling the female component, because male mutations would increase through both pollen and seeds whereas female mutations would increase only through seeds. Despite many studies on the genetic basis of loss of SI in the predominantly selfing plant Arabidopsis thaliana, it remains unknown whether selfing arose through mutations in the female specificity gene (S-receptor kinase, SRK), male specificity gene (S-locus cysteine-rich protein, SCR; also known as S-locus protein 11, SP11) or modifier genes, and whether any of them rose to high frequency across large geographic regions. Here we report that a disruptive 213-base-pair (bp) inversion in the SCR gene (or its derivative haplotypes with deletions encompassing the entire SCR-A and a large portion of SRK-A) is found in 95% of European accessions, which contrasts with the genome-wide pattern of polymorphism in European A. thaliana. Importantly, interspecific crossings using Arabidopsis halleri as a pollen donor reveal that some A. thaliana accessions, including Wei-1, retain the female SI reaction, suggesting that all female components including SRK are still functional. Moreover, when the 213-bp inversion in SCR was inverted and expressed in transgenic Wei-1 plants, the functional SCR restored the SI reaction. The inversion within SCR is the first mutation disrupting SI shown to be nearly fixed in geographically wide samples, and its prevalence is consistent with theoretical predictions regarding the evolutionary advantage of mutations in male components.