Chloroplast Gene Transmission in Chlamydomonas somatic fusion products : Effects of pretreatment with isolated flagella.

In sexual crosses between the two mating types of Chlamydomonas reinhardtii the progeny normally only receive chloroplast genes from the mt (+) parent. This pattern of inheritance is not seen following the rare mating events leading to the formation of vegetative diploids, or when the cells are fused using polyethylene glycol (PEG). Vegetative diploids usually carry chloroplast genes from both parents, and most of those that are uniparental carry the maternal parent's genes. In a PEG fusion the products are evenly divided among those uniparental for each of the parental chloroplast markers and those that are biparental. However, fusion in a sexual cross is usually preceded by the flagellaragglutination of the two mating types. When cells undergoing PEG fusion have been pretreated with isolated gametic flagella the transmission pattern in changed. If two mt (+) cells were fused, and one of them had been pretreated with isolated mt (-) flagella, then the majority of the progeny carried chloroplast genes only from the treated parent. This suggests that the signal for the induction of the events leading to uniparental maternal inheritance is the agglutination between mt (+) and mt (-) flagella that precedes cell fusion, and that the subsequent fate of chloroplast genes is controlled primarily by the mt (+) parent.