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

绿藻Closterium ehrenbergii自然种群的大多数克隆分离物表现出异质性，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克隆有关的杂交后代中获得了自交克隆，这被解释为具有独特的染色体重排。虽然这些自交克隆来自异源亲本，但与同系菌株一样，它们可以在同一个克隆的细胞之间形成合子。所有的自交无性系都可以认为是mt^-，因为它们与任何mt^+无性系都能很好地杂交，并证明它们继承了J5-48-2亲本的mt^-等位基因。尽管如此，它们也可以与任何Mt^-克隆人杂交。杂交受精卵产生高活力的后代，而自交受精卵产生极低活力的后代。当自交亲本与m1^+无性系杂交或与mt^-无性系杂交时，后代中出现自交无性系。通过分裂和再克隆多对配子节细胞，我们证实了自交克隆在有丝分裂的营养生长过程中，除了细胞继续自交外，还产生mt^+和mt^-细胞。我们讨论了埃伦伯丁自交可能通过从mt^-到mt^&lt；+的单向基因转化而发生的可能性。&gt；

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^<+. >