RESUMO
Alfalfa (Medicago sativa L.) is a widely grown perennial leguminous forage crop with a number of positive attributes. However, despite its moderate ability to tolerate saline soils, which are increasing in prevalence worldwide, it suffers considerable yield declines under these growth conditions. While a general framework of the cascade of events involved in plant salinity response has been unraveled in recent years, many gaps remain in our understanding of the precise molecular mechanisms involved in this process, particularly in non-model yet economically important species such as alfalfa. Therefore, as a means of further elucidating salinity response mechanisms in this species, we carried out in-depth physiological assessments of M. sativa cv. Beaver, as well as transcriptomic and untargeted metabolomic evaluations of leaf tissues, following extended exposure to salinity (grown for 3-4 weeks under saline treatment) and control conditions. In addition to the substantial growth and photosynthetic reductions observed under salinity treatment, we identified 1233 significant differentially expressed genes between growth conditions, as well as 60 annotated differentially accumulated metabolites. Taken together, our results suggest that changes to cell membranes and walls, cuticular and/or epicuticular waxes, osmoprotectant levels, antioxidant-related metabolic pathways, and the expression of genes encoding ion transporters, protective proteins, and transcription factors are likely involved in alfalfa's salinity response process. Although some of these alterations may contribute to alfalfa's modest salinity resilience, it is feasible that several may be disadvantageous in this context and could therefore provide valuable targets for the further improvement of tolerance to this stress in the future.
RESUMO
Alfalfa (Medicago sativa L.) is an extensively grown perennial forage legume, and although it is relatively drought tolerant, it consumes high amounts of water and depends upon irrigation in many regions. Given the progressive decline in water available for irrigation, as well as an escalation in climate change-related droughts, there is a critical need to develop alfalfa cultivars with improved drought resilience. M. sativa subsp. falcata is a close relative of the predominantly cultivated M. sativa subsp. sativa, and certain accessions have been demonstrated to exhibit superior performance under drought. As such, we endeavoured to carry out comparative physiological, biochemical, and transcriptomic evaluations of an as of yet unstudied drought-tolerant M. sativa subsp. falcata accession (PI 641381) and a relatively drought-susceptible M. sativa subsp. sativa cultivar (Beaver) to increase our understanding of the molecular mechanisms behind the enhanced ability of falcata to withstand water deficiency. Our findings indicate that unlike the small number of falcata genotypes assessed previously, falcata PI 641381 may exploit smaller, thicker leaves, as well as an increase in the baseline transcriptional levels of genes encoding particular transcription factors, protective proteins, and enzymes involved in the biosynthesis of stress-related compounds. These findings imply that different falcata accessions/genotypes may employ distinct drought response mechanisms, and the study provides a suite of candidate genes to facilitate the breeding of alfalfa with enhanced drought resilience in the future.