Whole genome sequence of Pyropia yezoensis (Rhodophyta) spore development mutant

Elucidation of the mechanisms of spore development is essential for understanding reproductive strategies, and is also important for improving cultivation in seaweed. In this study, we isolated a mutant with defects in spore development in Pyropia yezoensis (Rhodophyta), among the genetic transformants generated by insertional mutagenesis. We also characterized the phenotype of the mutant and identified the genomic region with the mutation. No differences were observed in the morphology of released spores between wild type and mutant strain; however, the mutant was less spore-releasing than wild type. Mutant's released spores retained their round shape under germination condition and no germination was observed in mutant. These results show that the main characteristics of this mutant are that it is poor in spore release and the released spores do not germinate. Whole genome sequences identified the introducing exogenous DNA was inserted into the nuclear genome of mutant, and suggested that there were duplication, deletion, and inversion in mutant's genome. Notably, a deletion of approximately 13 kbp was detected in the mutant's genome flanking the insertion, and this region contained a plant homeodomain. These findings suggest that the homeodomain-containing protein is involved in the regulation of spore development in P. yezoensis.