Valenti, G.; Sutera, A.; Dattolo, E.; Carimi, F.; Procaccini, G.; Mercati, F.; Puccio, G.; De Michele, R.

Seagrasses are marine angiosperms forming extensive underwater meadows that provide habitat, stabilize sediments, store carbon, and protect coastlines. Posidonia oceanica is the endemic foundation seagrass species of the Mediterranean, yet its meadows are rapidly declining. Despite its ecological importance, the molecular basis of P. oceanica development remains poorly understood. Here, we analyzed gene expression in roots, leaves, and seeds across four developmental stages, revealing strong tissue-specific patterns and temporally regulated expression dynamics. Leaves exhibited active regulation of photosynthesis-related processes, while roots were enriched in pathways linked to carbohydrate metabolism and cell wall biogenesis, supporting primary root growth and establishment. Seeds retained metabolic activity, with glycolytic enzymes indicating readiness for germination. Temporal analyses identified a major transcriptional shift, with distinct gene sets sequentially activated during early establishment and late maturation across tissues. Weighted Gene Co-expression Network Analysis identified modules strongly associated with specific tissues and developmental transitions, highlighting key hub genes involved in photosynthesis, metabolism, cell wall remodeling, and protein synthesis. Together, these results reveal complex, temporally coordinated regulatory networks underlying P. oceanica development.