In silico perspectives on RuBisCo activase and its role in mangrove CO2 sequestration

Blue carbon, or carbon fixation, can reduce global CO2 emissions through green ecosystems. The capacity of mangroves to fix atmospheric CO2 is five times higher than tropical or terrestrial land plants. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) is one of the most important enzymes for improving photosynthetic efficiency, but a range of sugar phosphates can restrict its activity. The AAA+ protein, RuBisCo activase (RCA), releases this inhibitory sugar-phosphate bound in the active site of RuBisCo by ATP hydrolysis. The present study focuses on understanding the mechanism by which RuBisCo activase regulates RuBisCo in mangroves. In terrestrial plants, RCA supports RuBisCo activity under stress; however, its efficiency diminishes under prolonged or extreme conditions, thereby limiting CO2 fixation. Mangroves, adapted to salinity, may harbour more stress-resilient mechanisms that help maintain photosynthesis. In silico analysis also revealed that mangrove RCA may exist in a hexameric form, with both the α- and β-isoforms indicating a level of structural diversification. Here, we describe a comparative study of RCA isoforms between terrestrial plants and mangroves, highlighting their structural and functional variations in response to environmental stress. We also investigated whether RuBisCo and its molecular chaperone, RCA, contribute significantly to CO2 sequestration in mangroves, or if their roles are minimal or even functionally divergent due to the prevalence of alternative carbon metabolic pathways in these stress-resilient environments.