What does the difference between the female and male gametophytes of Saccharina japonica remind us of

Abstract

The diploid sporophytes of brown seaweed, Saccharina japonica (Aresch.) C.E. Lane, C. Mayes, Druehl et G.W. Saunders, produce spores after meiosis, which develop into haploid female and male gametophytes with a sex ratio of 1:1. This ratio, as well as the results that all gametophytes produced by zoospores generated by parthenogenetic sporophytes are females, suggest that an X/Y-like sex-determination system exists in S. japonica. To understand the molecular differences between female and male gametophytes, a suppression subtractive cDNA library was constructed. It was found that lhcf6 was one of the differentially expressed genes, and that this differential transcription between the kelp female gametophytes and male ones might result from different promoters. Although no sex-specific genes were screened, several sex-related molecular markers were developed. Based on the high quality chromosomes prepared by pretreatment with multi-enzymes, two molecular markers in relation to the female gametophytes were co-localized on the sporophyte chromosomes, indicating they are female chromosome-specific cytogenetic DNA markers. Whether S. japonica possesses a sex chromosome might be resolved by pairing the kelp sporophyte chromosomes with the help of localized repetitive sequences such as telomere and centromere using fluorescence in situ hybridization techniques.