Leaf traits in P h aseolus vulgaris and Phaseolus acutifolius reveal divergent terminal drought coping strategies

Phaseolus beans play a crucial role in global food security, providing a sustainable source of protein and micronutrients for diverse populations. However, their productivity is severely affected by prolonged drought during the reproductive stage (terminal drought), which drastically reduces grain yield and quality. While substantial progress has been made in understanding plant drought responses during the vegetative stage, less is known about the responses during the reproductive phase. Among the different responses, little is known about the accompanying anatomical and physiological changes across plant organs. In particular, the leaf plasticity in response to environmental fluctuations remains unexplored under terminal drought. This study investigates the anatomical, physiological and molecular leaf responses to terminal drought in two resistant genotypes of Phaseolus vulgaris (common bean) and Phaseolus acutifolius (tepary bean). Despite comparable water status under stress, tepary mature leaves present longer major veins, larger xylem area, increased air space, and thicker cuticles than common bean. These traits likely contribute to improve water transport and gas exchange. Consistently, tepary bean maintained higher photosynthetic performance under well-watered and drought conditions, with considerable superior carbon fixation rates under irrigation. Elevated starch and sucrose accumulation in tepary leaves under both treatments further supports its enhanced carbon assimilation. RNAseq analysis indicated that some of these traits are partly transcriptomic dependent. Together, our findings highlight the diverse leaf-level adaptations that underlie terminal drought resistance in these species. The enhance anatomical and physiological traits in tepary bean offer valuable insights for improving drought resilience in common bean in a changing climate.