Ozias-Akins P, Roche D, Hanna W W
Department of Horticulture, University of Georgia Coastal Plain Experiment Station, Tifton, GA 31793-0748, USA.
Proc Natl Acad Sci U S A. 1998 Apr 28;95(9):5127-32. doi: 10.1073/pnas.95.9.5127.
Apomixis is a naturally occurring mode of reproduction that results in embryo formation without the involvement of meiosis or fertilization of the egg. Seed-derived progeny of an apomictic plant are genetically identical to the maternal parent. We are studying a form of apomixis called apospory that occurs in the genus Pennisetum, a taxon in the grass family. A cultivated member of this genus, pearl millet (Pennisetum glaucum), reproduces sexually. A wild relative of pearl millet, Pennisetum squamulatum, that is an obligate aposporous species, is cross-compatible with pearl millet when used as a pollen donor in the interspecific cross. We present herein the genetic mapping of 13 molecular markers in an interspecific hybrid population of 397 individuals that segregates for apomixis and sexuality. Surprisingly, 12 of the 13 markers strictly cosegregated with aposporous embryo sac development, clearly defining a contiguous apospory-specific genomic region in which no genetic recombination was detected. Lack of or suppression of recombination may be coincidentally associated with the chromosomal context of the apomixis locus or it may be a consequence of its evolution that is essential for preservation of gene function as has been previously shown in studies of complex loci in both plant and animal species.
无融合生殖是一种自然发生的繁殖方式，其导致胚胎形成而不涉及减数分裂或卵子受精。无融合生殖植物的种子衍生后代在基因上与母本相同。我们正在研究一种发生在狼尾草属（禾本科的一个分类群）中的无融合生殖形式——无孢子生殖。该属的一个栽培种珍珠粟（Pennisetum glaucum）进行有性繁殖。珍珠粟的一个野生近缘种——鳞稃狼尾草（Pennisetum squamulatum），是一种专性无孢子生殖物种，在种间杂交中用作花粉供体时，它与珍珠粟具有杂交亲和性。我们在此展示了在一个由397个个体组成的种间杂交群体中13个分子标记的遗传图谱，该群体在无融合生殖和有性生殖方面存在分离。令人惊讶的是，13个标记中的12个与无孢子胚囊发育严格共分离，明确界定了一个连续的无孢子生殖特异性基因组区域，在该区域未检测到基因重组。重组的缺乏或抑制可能与无融合生殖基因座的染色体背景巧合相关，或者它可能是其进化的结果，这对于基因功能的保存至关重要，正如先前在植物和动物物种的复杂基因座研究中所显示的那样。
