Palomar, V. M. | bioRxiv Science

bioRxiv2025

Leaf traits in Phaseolus 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. HighlightLeaf vein structure, xylem vessels density, and cuticle thickness enhance carbon assimilation and functional maintenance in tepary bean under drought during the reproductive stage, revealing key traits for common bean improvement.

plant biology↗

bioRxiv2023

Transcription-directed membrane association organizes the chloroplast nucleoid structure

DNA is organized into chromatin-like structures, which support the maintenance and regulation of genomes. A unique and poorly understood form of DNA packaging exists in chloroplasts, which are endosymbiotic organelles responsible for photosynthesis. Chloroplast genomes, together with associated proteins, form membraneless structures known as nucleoids. The internal arrangement of the nucleoid, molecular mechanisms of DNA packaging, and connections between nucleoid structure and gene expression remain mostly unknown. We show that Arabidopsis thaliana chloroplast nucleoids have a unique organization driven by DNA binding to the thylakoid membranes. DNA associated with the membranes has high protein occupancy, reduced DNA accessibility, and is highly transcribed. In contrast, genes with low levels of transcription are further away from the membranes, have lower protein occupancy, and higher DNA accessibility. Disruption of transcription at specific genes in sigma factor mutants causes a corresponding reduction in membrane association, indicating that RNA polymerase activity causes DNA tethering to the membranes. We propose that transcription organizes the chloroplast nucleoid into a transcriptionally active membrane-associated core and a less active periphery.

plant biology↗