Altered cell wall properties in domesticated cotton enhance CO2 diffusion conductance

The cell wall plays a key role in determining mesophyll conductance (gm) and photosynthetic capacity. While the impact of wall thickness (Tcw) on gm is well understood, the influence of wall composition and structural interactions on Tcw and gm remains unclear, and it is unknown whether these factors have been affected during crop domestication. In this study, we examined 25 wild and 13 domesticated Gossypium genotypes to investigate whether variations in Tcw, composition, and structure affected gm and photosynthesis. X-ray diffraction was used to analyze internal cell wall structure. Cotton domestication reduced Tcw by modifying the pectin-to-(cellulose+hemicellulose) ratio and increasing cellulose crystallinity. However, cell wall composition and structure regulate gm differently in wild and domesticated genotypes. In wild genotypes, the pectin-to-(cellulose+hemicellulose) ratio influences CO2 diffusion, while in domesticated genotypes, the pectin matrix may be more compact, making 1/(pectin+cellulose+hemicellulose) a better predictor, reflecting the internal property differences of the cell wall. We suggest that the exceptionally low Tcw values reported in cotton domesticated genotypes indicate that they have reached the lower limit, which may impose physical constraints on component proportions and conformation.