Undaria pinnatifida is an economically important brown macroalga in China. There are three sexual phenotypes (female, male, and monoicous) in the haploid gametophytes of U. pinnatifida. However, the sex-determining mechanisms remain unknown.
Recently, a research team led by Prof. PANG Shaojun from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) has identified a genomic region related to sex determination of U. pinnatifida through genomic resequencing and genetic linkage analyses of a segregating gametophyte family.
The study was published in Journal of Phycology on Nov. 4.
The researchers established a segregating gametophyte family that was derived from meiosis of a hybrid sporophyte between a monoicous gametophyte clonal line (male role) and a female one. They re-sequenced the family based on the male genome of U. pinnatifida and constructed a high-density genetic linkage map using 9,887 single nucleotide polymorphisms (SNPs), with an average distance of 0.41 centimorgan (cM) between adjacent SNPs.
Sixty-two SNPs were found to be tightly linked with sex phenotype based on the genetic map and these SNPs were at a position of 67.67 cM on the linkage group 23, corresponding to a physical range of 14.67 Mbp on the chromosome 23.
The researchers also reanalyzed the previous specific length amplified fragment sequencing data according to the reference genome and identified a sex-linked genomic region that contained the above-mentioned 14.67 Mbp region. Thus, they predicted that this overlapped genomic range is the sex-determining region. "We found 129 genes within this region, including the candidate male sex-determining gene encoding the high mobility group (HMG) domain protein," said Prof. SHAN Tifeng, first author of the study.
They also found that the HMG gene was expressed higher in vegetative male gametophytes, and in both the vegetative and gametogenesis phases of monoicous gametophytes, but significantly lower in the gametogenesis phase of male gametophytes.
"Now we are sequencing the genomes of female and monoicous sex. Once finished, we can compare the genomic difference of three different sexual phenotypes," said Prof. PANG, corresponding author of the study.
