HAP2/GCS1 Is Involved in the Sexual Reproduction System of the Marine Macroalga Ulva compressa (Ulvales, Chlorophyta)

Abstract

Summary 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 and mt + ) in the marine macroalga Ulva compressa and found that identical genomic regions homologous with HAP2/GCS1 existed in their draft genome sequences. Although an RNA-Seq analysis revealed that a variety of transcripts was expressed from the two regions containing HAP2/GCS1 in both the gamete and gametophyte of the mt and mt + genotypes, a putative transcript coding a protein containing a HAP2-GCS1 domain was identified only in the mt gamete. Immunofluorescence observations using an antibody against the putative HAP2/GCS1 demonstrated that the HAP2/GCS1 translational products localized to the cellular surface between the two flagella at a potential site for the mt mating structure. The antibody inhibited mating of the mt gamete with the mt + gamete in U. compressa. Our data suggest that HAP2/GCS1 functions in the mt gamete and plays a role in gamete fusion. Moreover, the specific function of HAP2/GCS1 in the mt mating type may be regulated by an alternative splicing mechanism in U. compressa.

Asexual thalli originated from sporophytic thalli via apomeiosis in the green seaweed Ulva

“…The mating structure at the tip of each gamete was observed and these structures corresponded to previous findings 23 . The conclusion that the function of the mating structure in the Ulvophyceae is for fertilization was also supported by the localization of membrane fusion protein HAP2/GCS1 24 . Conversely, in the biflagellate zoosporoids, no mating structure could be found on the eyespot side or the side opposite from the eyespot, even in the samples collected in the field or from isolated cultures.…”

Genomic structure and evolution of the mating type locus in the green seaweed Ulva partita

“…On the other hand, there are no differences in gametophytes between mating types in U . partita , but there are some differences in gametes with asymmetry of mating structure and eye spot and mt − -specific fusion machinery 25 , 37 . To analyze the expression levels of the U .…”

A Transformation System Using rbcS N-Terminal Region Fused with GFP Demonstrates Pyrenoid Targeting of the Small Subunit of RubisCO in Ulva compressa

“…U. compressa is used as a model organism of macro green algae, and its genome sequence is under analysis. The establishment of a transformation system for U. compressa would provide advantages for the characterization of interesting genes isolated from the genome, such as the male-specific HAP2/GCS1 involved in conjugation (Yamazaki et al 2014). However, a transient transformation method that can consistently accomplish 1% gene expression frequency has not been reported for macro green algae.…”