The involvement of an HMG-box gene in germ cell genesis in Pyropia haitanensis

High mobility group (HMG)-box proteins play important roles in sex differentiation and determination of fungi, brown algae, and vertebrates. So far, the HMG-box genes from the red algal species have not been explored, and their function in this lineage is still unknown. In this study, based on homologous searching approach, solo member of HMG-box gene (PhHMG) was identified from the genomes of Pyropia haitanensis, the number of which was far less than that of brown algae, green algae, and higher plants. The PhHMG protein contains three HMG-box domains and is localized in the nucleus and cell membrane region according to subcellular localization analysis. Further gene expression analysis indicated that PhHMG may involve in the germ cells genesis. As no germ cells (carpogonia or spermatangium) appeared in 30-days aged blades of P. haitanensis, PhHMG was not expressed or slightly expressed. Accompanied by the gradually appeared germ cells, the expression level of PhHMG gradually increased, with no difference between female and male strains. In addition, the 40-days aged blades of WT-10 strain (female) had more carpogonia at the apical parts, followed by the middle parts, and almost no carpogonia at the basal parts, and the expression of PhHMG showed a consistent trend of apical > middle > basal. This study has fundamental reference value in revealing the reproductive regulation mechanism and developing molecular assisted breeding of P. haitanensis.