Primary Characterization of a Life-Cycle Mutant akasusabi of the Red Alga Neopyropia yezoensis

Abstract

Gametophyte-to-sporophyte transition in the haploid-diploid life cycle depends on fertilization of male and female gametes. We describe here a mutant of the marine red seaweed Neopyropia yezoensis, designated akasusabi (aks), where the gametophyte-to-sporophyte transition occurs independently of fertilization. Although conchocelis filaments were produced from carpospores, severe defects in the maturation of carposporangia via mitosis to generate conchospores were observed. In the aks mutant, however, somatic cells of gametophytic thalli were able to produce conchocelis filaments without fertilization. Thus, apogamy occurs in aks. In addition, aks was highly sensitive to wounding that promotes both asexual and apogamous reproductive responses by producing spores, which develop either into blades or conchocelis filaments, indicating that aks responds to wounding by enhanced reproduction. These findings indicated that the aks mutation enables the transformation of vegetative cells to carpospores to produce sporophytes by apogamy and wound-inducible life cycle trade-off, stimulating a reset of the timing of reproduction during the life cycle. Therefore, AKS is involved in regulations of the gametophyte-to-sporophyte transition and asexual spore production in N. yezoensis.