A study of interconversion of mating systems in desmids as inferred from selfing in Closterium ehrenbergii

从绿色新月藻自然群体中分离的克隆菌株，如果不是全部的话，也是大多数都表现出异宗配合，这是由交配型（mt）基因座上的一对等位基因控制的。然而，我们在与mt^- J5-48-2克隆杂交的后代中获得了自交克隆，该克隆被解释为具有独特的染色体重排。这些自交系虽然来源于异宗配合亲本，但与同宗配合系一样，也能在同一单克隆细胞间形成合子。所有自交系基本上都可以被认为是mt^-，因为它们与任何mt^+无性系杂交都很好，结果证明它们从J5-48-2亲本遗传了mt^-等位基因。尽管如此，它们也可以与任何mt^-克隆体杂交。杂交合子产生高活力的后代，但自交合子产生极低的活力后代。当自交亲本自交或与mi^+无性系杂交而不与mt^-无性系杂交时，后代中会出现自交无性系。通过分裂和再克隆一些成对的接合配子膜细胞，我们证实了在营养生长过程中通过有丝分裂的细胞，除了继续自交的细胞外，自交克隆还产生mt^+和mt^-细胞。讨论了C. Ehrenbertism可能是通过从mt^-到mt^<+的单向基因转换而发生的。>

Most if not all clonal isolates from natural populations of the green alga Closterium ehrenbergii show heterothallism which is controlled by a pair of alleles at the mating-type(mt)locus, we obtained, however, selfing clones in progeny of a cross involving the mt^- J5-48-2 clone which was interpreted as having unique chromosomal rearrangements. Although derived from heterothallic parents, these selfing clones could form zygotes between cells of the same single clone as do homothallic strains. All the selfing clones could be considered basically as mt^-, because they were crossed well with any mt^+ clone and turned out to inherit the mt^- allele from the J5-48-2 parent. Nonetheless, they could be crossed with any mt^- clone as well. Crossed zygotes yielded high-viability progeny, but selfed zygotes gave rise to extremely low-viability progeny. Selfing clones appeared in progeny when a selfing parent was selfed or crossed with a mi^+ clone but not with a mt^- clone. By spliting and recloning a number of pairs of conjugating gametangial cells, we confirmed that a selfing clone produce both mt^+ and mt^- cells, in addition to cells continuing selfing, during vegetative growth by mitotic cell divisions. We discuss the possibility that selfing in C. ehrenbergii may occur by unidirectional gene conversion from mt^- to mt^<+. >