Greater leaf photosynthesis in the field by increasing mesophyll conductance via modified cell wall porosity and thickness in tobacco

Abstract

AbstractMesophyll conductance (gm) describes the ease with which CO2passes from the sub-stomatal cavities of the leaf to the primary carboxylase of photosynthesis, Rubisco. Increasinggmhas been suggested as a means to engineer increases in photosynthesis by increasing [CO2] at Rubisco, inhibiting oxygenation and accelerating carboxylation. Here tobacco was transgenically up-regulated with Arabidopsis Cotton Golgi-related 3 (CGR3), a gene controlling methylesterification of pectin, as a strategy to increase CO2diffusion across the cell wall and thereby increasegm. Across three independent events in tobacco strongly expressingAtCGR3,mesophyll cell wall thickness was decreased by 7-13%, wall porosity increased by 75%, andgmmeasured by carbon isotope discrimination increased by 28%. Importantly, field-grown plants showed an average 8% increase in leaf photosynthetic CO2uptake. UpregulatingCGR3provides a new strategy for increasinggmin dicotyledonous crops, leading to higher CO2assimilation and a potential means to sustainable crop yield improvement.