Transcriptomics of the chilling stress response of Kandelia candel

Comparing closely related species with differing abiotic stress tolerances can reveal physiological and genetic mechanisms that underlie environmental adaptations. Mangroves, found primarily in tropical and subtropical coasts, are expanding poleward due to rising minimum temperatures, for which species-specific cold tolerance likely influence expansion limits. In the Indo-West Pacific, Kandelia obovata tolerates chilling temperatures below 10 degrees celcius, while its sister species, Kandelia candel, is highly sensitive to chilling and restricted to tropical regions. The discrepancy of such adaptation offers unique materials for understanding chilling tolerance mechanisms. This study compares chilling-induced changes in photochemical efficiency, enzymatic activity and gene expression between the two species to reveal their differences in photoprotective strategies. We specifically focus on the impact of chilling on the light reactions of photosynthesis as one of the primary impacts of chilling on plant species is chilling induced photoinhibition. Despite maintaining higher photochemical efficiency, K. obovata exhibited increased reactive oxygen species (ROS) levels and lower antioxidant enzyme activity compared to K. candel during chilling at 10 degrees celcius. Furthermore, interspecies comparison of the expression of genes involved in photoprotection during chilling stress revealed divergent regulation of PGR5 and CHL, which regulate cyclic electron flow and non-photochemical quenching. The upregulation of these genes in K. obovata and their downregulation in K. candel suggest that differences in photoprotective responses may contribute to the contrasting chilling tolerances of these species. These findings highlight a potential mechanism that contributes to the cold tolerance and biogeographical distributions of subtropical and tropical plant species, emphasizing the need for further comparative studies across a broader range of taxa.