Functional characterization of putrescine biosynthesis in the early development of conchospores in the red seaweed Pyropia yezoensis.

The current seedling production system for Pyropia primarily relies on the collection of conchospores, which serve as seeds to produce germlings for open-sea aquaculture. Following their release from shell-borne conchocelis, conchospores undergo adhesion to seedling ropes, cell polarization, meiosis to form tetrads, and subsequent mitotic divisions to develop into germlings. the efficiency of conchospore-to-germling development is critical for aquaculture yield. In this study, we demonstrate that putrescine (PUT) plays important roles during the early development of conchospores. We analyzed differential gene expression profiles across conchospore development and identified key genes involved in PUT biosynthesis-including ornithine decarboxylase (ODC), arginine decarboxylase (ADC), and N-carbamoylputrescine amidohydrolase (CPA)-which showed significantly increased transcriptional levels in polarized conchospores and germlings. A corresponding rise in cellular PUT content was also observed. Exogenous PUT application significantly enhanced both the polarization ratio and meiosis ratio. In contrast, the ODC-specific inhibitor DFMO strongly suppressed polarization, meiosis, as well as the onset of mitosis when added at the meiotic stage. Transient silencing of PyODC expression via siRNA transfection arrested conchospores at the initial released stage. Moreover, exogenous PUT supplementation in PyODC-silenced conchospores partially rescued polarization and meiotic ratios, further underscoring the essential roles of PyODC and its catalytic product PUT in early conchospore development. Our findings elucidate the molecular mechanisms underlying Pyropia conchospore development and offer potential technical strategies to improve germling production through precise metabolic regulation in Pyropia seedling production system.