Comparative analysis of Rubisco expression in three different coral species: Implications for bleaching susceptibility

This study examined the expression of the Rubisco gene in symbiotic dinoflagellates associated with three scleractinian coral species ( Montastrea cavernosa , Orbicella faveolata , and Orbicella annularis ) that were exposed to seasonal thermal stress. Coral fragments were collected in June and October of 2022 at Manchoncitos Reef in Playa Paraiso, Quintana Roo, Mexico (20°45′34″N, 86°57′00″W). Total RNA was extracted and reverse transcribed into cDNA. Rubisco gene expression was then quantified for quantitative PCR. Statistical differences were evaluated using a two-way ANOVA. All coral species exhibited significantly higher Rubisco expression in June (28.7°C) and significantly lower expression in October (30.8°C). The greatest reduction was detected in M. cavernosa , while O. faveolata and O. annularis showed more moderate decreases. During the October sampling period, bleaching was evident in colonies of O. annularis and O. faveolata but not in M. cavernosa . These findings suggest that M. cavernosa may mitigate oxidative stress by suppressing Rubisco under thermal stress, thereby minimizing oxygenase activity and reactive oxygen species production. This study supports the hypothesis that species-specific regulation of Rubisco expression is linked to differential thermal tolerance and highlights its potential as a molecular biomarker for the early detection of thermal stress in reef corals. These results further our understanding of coral-symbiont stress responses and inform strategies for reef conservation and restoration, particularly in identifying thermotolerant coral holobionts.