Sex-Specific Cell Fusion Pattern of Isogametes in Marine Green Alga, <i>Acetabularia caliculus</i> (Ulvophyceae, Chlorophyta)

Abstract

Summary Using field emission scanning electron microscopy (FE-SEM) and fluorescence microscopy, the respective relations between the arrangements of the gamete cell fusion site and the inheritance pattern of chloroplast DNA (cp-DNA) as a sex-specific marker were studied for the isogamous dasycladalean alga Acetabularia caliculus. The gamete had two flagella elongated from the cell anterior. One oval-shaped eyespot situated on the cell posterior was visualized using FE-SEM. When the gametes belonging to the opposite mating types were mixed together, the two gametes aligned side-by-side at their lateral side and fused to form a quadriflagellate planozygote. In the planozygote, the two flagella from the opposite mating type gametes lay side-by-side and two eyespots aligned on the same side of the cell, suggesting opposite positioning of the cell fusion sites between two parental gametes. To confirm whether the gamete fusion pattern observed in the planozygotes was a result of sex-specific fusion or not, the inheritance pattern of cp-DNA was observed using fluorescence microscopy after staining with DAPI concomitantly with the cell fusion pattern. When the eyespots were used as positional marker and were viewed from the surface that included the eyespots, the chloroplast of one parental gamete was found to contain cp-DNAs, although cp-DNAs were not detected in the chloroplast derived from another parental gamete. These results suggest that the gamete fusion pattern observed by FE-SEM was a result of sex-specific fusion.

Gamete dimorphism of the isogamous green alga (Chlamydomonas reinhardtii), is regulated by the mating type-determining gene, MID

“…cytoplasmic inheritance of organelles) is not always invariable among C. reinhardtii, Ulva and other ulvophycean species; chloroplast DNA is usually inherited by progeny from type α gametes (mt + ) in C. reinhardtii 43 , type β gametes (mt + ) in U. partita 17,44 and type β gametes (females, mt + ) in other ulvophycean species (e.g. Bryopsis maxima and Acetabularia caliculus) 9,[45][46][47][48] , whereas mitochondrial DNA is inherited by progeny from type β gametes (mt -) in C. reinhardtii 49 , type α/β gametes (mt + ) in U. partita 50 , and type β gametes (females) in B. maxima 45,46 (Table 2), suggesting that the genetic pathway that determines these mating type-specific traits in Ulva and other ulvophycean species is not necessarily the same as that of C. reinhardtii. Despite these differences, the dominant mating type was commonly associated with a particular MSP phenotype (type β) in C. reinhardtii and U. prolifera (Table 2), which was clarified using heterozygous diploid gametes harbouring both mt + and mtgenomes.…”

Sex‐specific Positioning of the Mating Structure in Scale‐bearing Gametes of Monostroma angicava and Collinsiella cava (Ulvophyceae, Chlorophyta): A Possible Widespread Difference between Male and Female Gametes

“…2005; Caulerpa , Miyamura and Nagumo 2007), and Dasycladales ( A . caliculus ; Miyamura and Nagumo 2016), the gamete type (α or β) is almost always correlated with the inheritance pattern of chloroplast DNA, which is one of the sex‐specific features of green algae (Miyamura 2010). Chloroplast DNA tends to be preferentially inherited from type β gametes (female) to the progeny in these ulvophycean algae, although it is inherited from type α, type β, and both types in some U .…”