Abstract
Common bean (Phaseolus vulgaris L.) is the main legume crop for direct human consumption worldwide. Among abiotic factors affecting common bean, drought is the most limiting. This study aimed at characterizing genetic variability and architecture of transpiration, stomatal regulation and whole plant water use within the Mesoamerican germplasm. A critical fraction of transpirable soil water (FTSWc) was estimated as the inflection point at which NTR starts decreasing linearly. Genome-wide association (GWA) analyses for mean NTR and FTSWc were performed. High variation on mean NTR and FTSWc was found among genotypes. Genomic signals controlling the variation of these traits were identified on Pv01 and Pv07 some located in intergenic, intronic and exonic regions. A set of novel candidate genes and putative regulatory elements located in these QTL were identified. Some of the genes have been previously reported to be involved in abiotic tolerance in model species, including some of the five transcription factors (TF) identified. Four candidate genes, one with potential water transportation activity and three TFs were validated. The gene Phvul.001G108800, an aquaporin SIP2-1 related gene, showed water channel activity through oocyte water assays. Mutant Arabidopsis thaliana (Ath) lines for the homologous genes of common bean were evaluated in transpiration experiments. Two of the three evaluated TFs, UPBEAT1 and C2H2-type ZN finger protein, were involved in the control of transpiration responses to drying soil. Our results provide evidence of novel genes to accelerate the drought tolerance improvement in the crop and study the physiological basis of drought response in plants.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Response: Thank you for your comment and insight. We hope that our additional research is sufficient to confirm the responses we have observed in bean. Although It is not a definitive account on the mechanisms, we feel that our work belongs in Plant Physiology as it spans various areas relevant to your readership, such as physiological mechanisms, genetics and breeding, molecular tools and bioinformatics. We feel it is also relevant to your readership as the results from our study have direct implications for the development of follow up field-based research approaches for the development of drought tolerance. Transpiration responses of plants to drying soil are key factors in studying the physiological basis of drought tolerance. We conducted a large-scale experiment analyzing the transpiration responses of common bean to drying soil. Candidate genes involved in the regulation of transpiration rates were identified through Genome-Wide Association (GWA) analyses, followed by functional studies to validate several of these candidate genes. Firstly, we examined the potential water channel activity of an aquaporin-related gene using oocyte swelling assays, synthesizing and expressing the native sequence of common bean. We demonstrated that the gene is involved in the water movement across membranes. Secondly, due to challenges in transformation and regeneration in common bean, we used mutant Arabidopsis plants to study homologous genes corresponding to the candidate genes. Using three Arabidopsis lines, we conducted two independent experiments replicating the conditions and analyses of transpiration rate measurements performed for common bean. Our results indicate that two out of the three evaluated transcription factors (TF) play roles in controlling transpiration in Arabidopsis. These findings provide novel insights into the physiological functions of the analyzed genes, with potential applications in crop improvement as well as in advancing understanding of the genetic control of water use in plants.
