Responses of seagrass ecotypes to a simulated marine heatwave: insights from transcriptomics and physiology
The most abundant South African seagrass, Zostera capensis, exhibits a wide yet disjunct distributional range in the coastal areas where it is mainly found in sheltered estuaries. Occurring in heterogenous environmental conditions across its bathymetric cline, this endangered seagrass exhibits two ecotypes with contrasting morpho-physiological responses to environmental stress. In this study, ecotypes were collected from Knysna Estuarine Bay and re-planted in mesocosm setup where a simulated marine heatwave (MHW) was used to investigate photosynthetic (Fv/Fm) and transcriptomic (RNA-Seq) responses of ecotypes. Following 30 days of acclimation (T0), plants were exposed to warming (T1) and allowed to recover for 7 days (T2) where at each time point Fv/Fm and gene expression profiles were measured. Results from the photo-physiology showed differential Fv/Fm responses between ecotypes at T2 which were also decreased compared to control conditions. On the other hand, results from transcriptomic analysis did not yield any differentially expressed gene (DEGs) between ecotypes. The recovery period (T2) was characterized by downregulation of DEGs involved in photosynthesis, light capture by chlorophyll, and homeostasis, suggesting that Z. capensis suffered irreversible damage to the photosynthetic machinery and that temperatures over are beyond its tolerant threshold. The lack of DEGs between ecotypes suggests an interesting phenomenon requiring other omics techniques such as proteomics and metabolomic which may significantly advance both molecular and physiological responses in pioneer species.