LAUSR

Saccharina japonica is an important cultured marine brown alga and it has been the subject of intensive genetic improvement during its domestication and farming. However, there are limited credible and effective sex markers to identify the sex of gametophytes and sporophytes derived from normal hybridization or monogenesis. In the present study, the transcriptomic and genomic sequences of S. japonica were screened by 15 sex-determining region (SDR) genes from a model brown alga (Ectocarpus), and six cDNA sequences and their corresponding genomic sequences were identified. Thirteen primer pairs were designed from the coding region of six genomic sequences and subsequently tested on gametophytes of S. japonica. From these regions, four novel male-specific markers were developed, which derived from S. japonica genomic sequences JXRI01001736 and JXRI01002827, corresponding to a male-specific SDR gene and a gametologue SDR gene in Ectocarpus, respectively. In addition, an existing female marker (M_68_58_2) for Macrocystis pyrifera and Undaria pinnatifida, derived from the Ectocarpus SDR gene, could also be used as a female-specific marker for S. japonica. The results of the present study not only demonstrate an important new tool to determine the sex of gametophytes and distinguish between diploid sporophytes and partheno-sporophytes in breeding programmes but also provide insight into the sex-determination system for S. japonica, including the identification of sex chromosomes, SDR, and SDR genes and evolution of sex chromosomes.