Research Group on Plant Biology under Mediterranean Conditions. Universitat de les Illes Balears-INAGEA, Palma 07122, Spain.
Research School of Biology, Australian National University, Canberra, ACT 2601, Australia.
Plant Physiol. 2023 Feb 12;191(2):946-956. doi: 10.1093/plphys/kiac492.
The CO2-fixing enzyme Ribulose bisphosphate carboxylase-oxygenase (Rubisco) links the inorganic and organic phases of the global carbon cycle. In aquatic systems, the catalytic adaptation of algae Rubiscos has been more expansive and followed an evolutionary pathway that appears distinct to terrestrial plant Rubisco. Here, we extend this survey to differing seagrass species of the genus Posidonia to reveal how their disjunctive geographical distribution and diverged phylogeny, along with their CO2 concentrating mechanisms (CCMs) effectiveness, have impacted their Rubisco kinetic properties. The Rubisco from Posidonia species showed lower carboxylation efficiencies and lower sensitivity to O2 inhibition than those measured for terrestrial C3 and C4-plant Rubiscos. Compared with the Australian Posidonia species, Rubisco from the Mediterranean Posidonia oceanica had 1.5-2-fold lower carboxylation and oxygenation efficiencies, coinciding with effective CCMs and five Rubisco large subunit amino acid substitutions. Among the Australian Posidonia species, CCM effectiveness was higher in Posidonia sinuosa and lower in the deep-living Posidonia angustifolia, likely related to the 20%-35% lower Rubisco carboxylation efficiency in P. sinuosa and the two-fold higher Rubisco content in P. angustifolia. Our results suggest that the catalytic evolution of Posidonia Rubisco has been impacted by the low CO2 availability and gas exchange properties of marine environments, but with contrasting Rubisco kinetics according to the time of diversification among the species. As a result, the relationships between maximum carboxylation rate and CO2- and O2-affinities of Posidonia Rubiscos follow an alternative path to that characteristic of terrestrial angiosperm Rubiscos.
固定 CO2 的酶核酮糖二磷酸羧化酶-加氧酶（Rubisco）将全球碳循环的无机相和有机相联系起来。在水生系统中，藻类 Rubisco 的催化适应性更为广泛，并遵循一种与陆地植物 Rubisco 明显不同的进化途径。在这里，我们将这一调查扩展到不同的波西多尼亚海草属物种，以揭示它们不同的地理分布和分化的系统发育，以及它们的 CO2 浓缩机制（CCM）的有效性，如何影响它们的 Rubisco 动力学特性。波西多尼亚物种的 Rubisco 的羧化效率较低，对 O2 抑制的敏感性也低于陆地 C3 和 C4 植物 Rubisco。与澳大利亚的波西多尼亚物种相比，地中海波西多尼亚海洋的 Rubisco 的羧化和加氧效率低 1.5-2 倍，这与有效的 CCM 和五个 Rubisco 大亚基氨基酸取代相吻合。在澳大利亚的波西多尼亚物种中，波西多尼亚 sinuosa 的 CCM 有效性较高，而深生的波西多尼亚 angustifolia 的 CCM 有效性较低，这可能与 P. sinuosa 的 Rubisco 羧化效率低 20%-35%以及 P. angustifolia 的 Rubisco 含量高两倍有关。我们的结果表明，海洋环境中 CO2 可用性和气体交换特性对波西多尼亚 Rubisco 的催化进化产生了影响，但根据物种分化的时间，Rubisco 动力学也有不同的特点。因此，波西多尼亚 Rubisco 的最大羧化速率与 CO2 和 O2 亲和力之间的关系遵循与陆地被子植物 Rubisco 不同的途径。
