Transcriptome responses of two Halophila stipulacea seagrass populations from pristine and impacted habitats to single and combined thermal and excess nutrient stressors reveal local adaptive features and core stress response genes

In their natural habitats seagrasses face multiple abiotic stressors However most studies investigating the effects of environmental stressors on seagrasses have focused on growth and physiological responses to single stressors Here we examined the transcriptome responses of the tropical seagrass Halophila stipulacea collected from a northern Gulf of Aqaba pristine site South Beach SB and an anthropogenicallyimpacted site Tur Yam TY grown in a mesocosm and exposed to ecologicallyrelevant single and combined thermal and excess nutrient stressors The combined thermalnutrient stressor elicited greater transcriptome reprogramming than the single stressors in both populations and induced the expresson of a combinationspecific set of genes involved in abiotic and biotic stress responses Furthermore thermal stress exerted a more dominant influence than excess nutrient stress upon the transcriptome response to the combined stress Transcriptomes of plants from the impacted TY site exhibited signatures of a stressready and primed transcriptome a more restrained transcriptome response the presence of genes exhibiting a stressready mode of expression under all stresses and a greater global foldchange in expression in response to excess nutrients We also identified core stressresponse genes that could be leveraged as early indicators of stress in the field Overall our data suggest that environmental conditions in seagrass habitats can drive local molecular adaptation and that the response of seagrasses to combined stressors associated with climate change and coastal development cannot be predicted from the response to single stressors