HAP2/GCS1 Is Involved in the Sexual Reproduction System of the Marine Macroalga<i> Ulva compressa</i> (Ulvales, Chlorophyta)
Gamete fusion or fertilization is one of the most important steps in sexual reproduction. HAP2/GCS1 is a potential gamete membrane fusion component. We analyzed whole genome sequences of two strains with opposite mating types (mt<sup>−</sup> and mt<sup>+</sup>) in the marine macroalga <i>Ulva compressa</i> and found that identical genomic regions homologous with <i>HAP2</i>/<i>GCS1</i> existed in their draft genome sequences. Although an RNA-Seq analysis revealed that a variety of transcripts was expressed from the two regions containing <i>HAP2</i>/<i>GCS1</i> in both the gamete and gametophyte of the mt<sup>−</sup> and mt<sup>+</sup> genotypes, a putative transcript coding a protein containing a HAP2–GCS1 domain was identified only in the mt<sup>−</sup> gamete. Immunofluorescence observations using an antibody against the putative HAP2/GCS1 demonstrated that the <i>HAP2</i>/<i>GCS1</i> translational products localized to the cellular surface between the two flagella at a potential site for the mt<sup>−</sup> mating structure. The antibody inhibited mating of the mt<sup>−</sup> gamete with the mt<sup>+</sup> gamete in <i>U. compressa</i>. Our data suggest that HAP2/GCS1 functions in the mt<sup>−</sup> gamete and plays a role in gamete fusion. Moreover, the specific function of HAP2/GCS1 in the mt<sup>−</sup> mating type may be regulated by an alternative splicing mechanism in <i>U. compressa</i>.
ＣＹＴＯＬＯＧＩＡ 79(4), 575-584, 2014