Cell wall composition in relation to photosynthesis across land plants' phylogeny: crops as outliers
In the present study, we combine published and novel data on cell wall composition and photosynthesis limitations, including data for all the major land plants phylogenetic groups. We provide novel evidence on the importance of cell wall composition in determining mesophyll conductance to CO2 diffusion (gm) across land plants phylogeny. We address the hypothesis that the pectin fraction of total major cell wall compounds is positively related to gm and, consequently, to photosynthesis, when pooling species from across the entire phylogeny. The role of cell wall composition in photosynthesis has only recently been proposed. Apparently contradictory results have been reported, but previous studies were often limited to single or closely related species. This is the very first report to show general relationships by considering species spanning the entire phylogeny of land plants. This study identifies a clear biochemical basis--one that can be traced back to specific genes-- for a large component of mesophyll conductance and, thus, photosynthetic capacity. It opens new avenues for improving the photosynthesis of terrestrial plants. Additionally, it suggests that current crops are already optimized and even uncoupled from these general relationships, raising questions about the regulation of gm in crop species.