Department of Plant Biology, Carnegie Institute for Science, Stanford, CA, 94305, USA.
Corn Insects and Crop Genetics Research Unit, USDA ARS, Ames, IA, 50011, USA.
Plant Reprod. 2020 Dec;33(3-4):117-128. doi: 10.1007/s00497-020-00394-w. Epub 2020 Aug 31.
Gametophytic cross-incompatibility systems in corn have been the subject of genetic studies for more than a century. They have tremendous economic potential as a genetic mechanism for controlling fertilization without controlling pollination. Three major genetically distinct and functionally equivalent cross-incompatibility systems exist in Zea mays: Ga1, Tcb1, and Ga2. All three confer reproductive isolation between maize or teosinte varieties with different haplotypes at any one locus. These loci confer genetically separable functions to the silk and pollen: a female function that allows the silk to block fertilization by non-self-type pollen and a male function that overcomes the block of the female function from the same locus. Identification of some of these genes has shed light on the reproductive isolation they confer. The identification of both male and female factors as pectin methylesterases reveals the importance of pectin methylesterase activity in controlling the decision between pollen acceptance versus rejection, possibly by regulating the degree of methylesterification of the pollen tube cell wall. The appropriate level and spatial distribution of pectin methylesterification is critical for pollen tube growth and is affected by both pectin methylesterases and pectin methylesterase inhibitors. We present a molecular model that explains how cross-incompatibility systems may function that can be tested in Zea and uncharacterized cross-incompatibility systems. Molecular characterization of these loci in conjunction with further refinement of the underlying molecular and cellular mechanisms will allow researchers to bring new and powerful tools to bear on understanding reproductive isolation in Zea mays and related species.
玉米的配子体不亲和性系统是一个多世纪以来遗传研究的主题。它们具有巨大的经济潜力，可以作为一种遗传机制，在不控制授粉的情况下控制受精。在玉米中存在三种主要的遗传上不同且功能上等效的不亲和性系统：Ga1、Tcb1 和 Ga2。这三个系统在任何一个位点上都赋予了不同单倍型的玉米或墨西哥类蜀黍品种之间的生殖隔离。这些位点赋予了丝和花粉具有遗传上可分离的功能：一种是雌性功能，允许丝阻止非自身类型花粉的受精；另一种是雄性功能，克服了来自同一基因座的雌性功能的阻碍。这些基因的鉴定揭示了它们赋予的生殖隔离。将雄性和雌性因素鉴定为果胶甲酯酶，揭示了果胶甲酯酶活性在控制花粉接受或拒绝之间的决定中的重要性，可能是通过调节花粉管细胞壁的甲酯化程度来实现的。果胶甲酯酶的适当水平和空间分布对花粉管的生长至关重要，这受到果胶甲酯酶和果胶甲酯酶抑制剂的影响。我们提出了一个分子模型，解释了不亲和性系统可能的作用机制，可以在玉米和未表征的不亲和性系统中进行测试。这些基因座的分子特征与潜在的分子和细胞机制的进一步细化将使研究人员能够利用新的和强大的工具来理解玉米和相关物种中的生殖隔离。
