Izumi Hikari, Nakai Yuji, Uji Toshiki, Nagaosa Kaz, Fukuda Satoru, Mizuta Hiroyuki, Saga Naotsune
Section of Food Sciences, Institute of Regional Innovation, Hirosaki University, Aomori, Aomori, Japan.
Division of Marine Life Science, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan.
J Phycol. 2025 Aug;61(4):805-819. doi: 10.1111/jpy.70026. Epub 2025 May 5.
Mechanistic elucidation of spore development is essential for understanding reproductive strategies and improving seaweed cultivation. In this study, we isolated a mutant with spore development defects in Pyropia yezoensis (Rhodophyta) from among genetic transformants generated via insertional mutagenesis. We characterized the mutant phenotype and identified the genomic region containing the mutation. The mutant produced spores (archeospores, zygotospores, and conchospores) at every relevant stage of the life history. No evident differences were observed in the appearance of the released spores at any stage under light microscopy between the wild-type and mutant strains; however, the mutant exhibited a trend of reduced spore release compared with the wild-type. Additionally, the archeospores released by the mutant remained round after being released from the sporangium, failed to adhere to the substratum, did not germinate, and showed no cell wall development after 4 days of standard culture, in contrast to the wild-type. Similar results were observed for the zygotospores and conchospores. These findings indicate that the main characteristic of this mutant was poor spore release, and the released spores failed to germinate. Whole-genome sequencing revealed the introduction of exogenous DNA into the nuclear genome of the mutant and suggested the presence of duplications, deletion, and inversion in the mutant genome. Notably, a deletion of approximately 13 kb was detected in the mutant genome flanking the insertion, and this region contained a plant homeodomain, suggesting that homeodomain-containing proteins may regulate spore development in P. yezoensis.
阐明孢子发育的机制对于理解海藻的繁殖策略和改进海藻养殖至关重要。在本研究中，我们从通过插入诱变产生的遗传转化体中分离出了一种在条斑紫菜（红藻门）中具有孢子发育缺陷的突变体。我们对该突变体的表型进行了表征，并确定了包含该突变的基因组区域。该突变体在生活史的每个相关阶段都能产生孢子（原始孢子、合子孢子和壳孢子）。在光学显微镜下，野生型和突变体菌株在任何阶段释放的孢子外观均未观察到明显差异；然而，与野生型相比，突变体表现出孢子释放减少的趋势。此外，与野生型相比，突变体释放的原始孢子从孢子囊释放后仍保持圆形，无法附着在基质上，不能萌发，在标准培养4天后也未显示细胞壁发育。合子孢子和壳孢子也观察到了类似的结果。这些发现表明，该突变体的主要特征是孢子释放不良，且释放的孢子无法萌发。全基因组测序揭示了外源DNA导入突变体的核基因组中，并表明突变体基因组中存在重复、缺失和倒位。值得注意的是，在插入位点侧翼的突变体基因组中检测到约13 kb的缺失，该区域包含一个植物同源结构域，这表明含同源结构域的蛋白质可能调控条斑紫菜的孢子发育。
