Carbon-concentrating mechanisms in pods are key elements for terminal drought resistance in Phaseolus vulgaris.

Common bean (Phaseolus vulgaris L.) is one of the most consumed legumes in the human diet and a substantial source of dietary protein. A major problem for this rainfed crop is the decrease in grain yield caused by prolonged drought periods during the reproductive stage of plant development (terminal drought). Terminal drought remains a prevailing threat to the farming of this staple, with losses reaching >80%. Based on the high correlation between the resistance of common bean to terminal drought and efficient photoassimilate mobilization and biomass accumulation in seeds, we aimed to identify mechanisms implicated in its resistance to this stress. We used two representative Durango race common bean cultivars with contrasting yields under terminal drought, grown under well-watered or terminal drought conditions. Using comparative transcriptomic analysis focused on source leaves, pods, and seeds from both cultivars, we provide evidence indicating that under terminal drought the resistant cultivar promotes the build-up of transcripts involved in recycling carbon through photosynthesis, photorespiration, and CO2-concentrating mechanisms in pod walls, while in seeds, the induced transcripts participate in sink strength and respiration. Physiological data support this conclusion, implicating their relevance as key processes in the plant response to terminal drought.