A modified protocol was developed to obtain high-quality total RNA from various mature organs, including leaves, seeds, pods and testae, from different cultivars of Phaseolus vulgaris L. grown under optimal conditions or subjected to severe drought; stress conditions leading to the accumulation of numerous secondary metabolites can affect RNA quality. This modified procedure is based on CTAB extraction protocols. Modifications in this protocol prevent oxidation of phenolic complexes, the precipitation of proteins, DNA and degradation of RNA; also, it is effective atremoving secondary metabolites. The RNA obtained following this procedure showed high quality as revealed by a high RNA integrity number and high 260/280nm (>2) ratio, therequirements needed to increase reliability of diverse molecular analyses.
Terminal drought stress affects more than half of the areas planted with common bean (Phaseolus vulgaris), the main food legume globally, generating severe yield losses. Phenotyping water deficit responses and water use are central strategies to develop improved terminal drought resilience. The exploration and exploitation of genetic diversity in breeding programs are gaining importance, with a particular interest in related species with great adaptation to biotic and abiotic factors. This is the case with tepary beans (Phaseolus acutifolius), a bean that evolved and was domesticated in arid conditions and is considered well adapted to drought and heat stress. Under greenhouse conditions, using one genotype of tepary beans (resistant to drought) and two of common beans (one resistant and one susceptible to terminal drought), we evaluated phenotypic differences in traits such as water use efficiency (WUE), transpiration efficiency, rate of photosynthesis, photosynthetic efficiency, stomatal density, stomatal index, stomatal size, and the threshold for transpiration decline under well-watered and terminal drought conditions. Our results indicate two different water use strategies in drought-resistant genotypes: one observed in common bean aimed at conserving soil water by closing stomata early, inhibiting stomatal development, and limiting growth; and the other observed in tepary bean, where prolonged stomatal opening and higher carbon fixation, combined with no changes in stomata distribution, lead to higher biomass accumulation. Strategies that contribute to drought adaptation combined with other traits, such as greater mobilization of photoassimilates to the formation of reproductive structures, confer bean drought resistance and are useful targets in breeding programs.
Common bean (Phaseolus vulgaris L.) is one of the most consumed legumes in the human diet. 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, TD). Despite the importance of the common bean as a substantial source of proteins, TD remains a prevailing threat to the farming of this staple, with losses reaching more than 80%. Based on the high correlation between the common bean resistance to TD with an efficient photo-assimilate 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 TD, grown under well-watered or TD conditions. By comparative transcriptomic analysis focused on source leaves, pods, and seeds from both cultivars, we provide evidence indicating that under TD the resistant cultivar promotes the buildup 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 TD.
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