Unlocking seagrass germination: divergent roles of strigolactones and karrikins in Zostera marina

Seagrasses, such as Zostera marina , play a crucial role in coastal ecosystems, yet the hormonal regulation of their seed dormancy and germination remains poorly understood. Strigolactones (SL) and karrikins (KAR), two plant growth regulators (PGRs) known to regulate germination and development in terrestrial plants, have recently been identified in marine angiosperms. However, their functional roles in seagrasses remain unexplored. Here, we provide the first assessment of SL and KAR effects on Z. marina seed germination and seedling development under controlled conditions. We tested the effect of ten different concentrations of SL and KAR on germination percentage, mean germination time, and seedling growth, considering multiple seed generations. SL significantly promoted germination, particularly at intermediate concentrations, and enhanced cotyledon growth, whereas KAR exerted a strong inhibitory effect, delaying or preventing germination. The identification of Z. marina orthologs of key SL and KAR signaling components suggests evolutionary conservation of these pathways in marine plants. Our findings provide new insights into the hormonal regulation of seagrass germination, highlighting both conserved and divergent functions of SL and KAR compared to terrestrial species. These results advance our understanding of hormonal control in marine plant species and hold implications for the conservation and restoration of seagrass meadows. Highlights This study provides the first experimental evidence of the effects of strigolactones (SL) and karrikins (KAR) on seed germination and seedling development in the seagrass Zostera marina .