The trajectory in catalytic evolution of Rubisco in Posidonia seagrass species differs from terrestrial plants.

This article investigates the catalytic evolution of Ribulose bisphosphate carboxylase-oxygenase (Rubisco) in seagrass species of the genus Posidonia, revealing that their Rubisco kinetics differ significantly from those of terrestrial plants. The study compares Mediterranean Posidonia oceanica with four Australian Posidonia species, finding that P. oceanica exhibits lower carboxylation and oxygenation efficiencies, linked to five unique amino acid substitutions in its Rubisco large subunit (RbcL) and more effective CO2 concentrating mechanisms (CCMs). Among Australian species, variations in CCM effectiveness correlate with differences in Rubisco kinetics and content, such as the lower carboxylation efficiency in P. sinuosa and higher Rubisco content in the deep-living P. angustifolia. Overall, Posidonia Rubiscos show slower catalytic turnover rates, lower CO2 affinity, and reduced sensitivity to O2 inhibition, following an alternative evolutionary trajectory distinct from terrestrial angiosperms, likely influenced by the marine environment’s low CO2 availability and gas exchange constraints.