Characterization of SPL9 role in drought stress tolerance in Medicago sativa

Climate change has caused previously ideal agricultural lands to experience events of drought resulting in decreases to crop yield. Understanding the molecular mechanisms that underpin the response of plants to drought stress is crucial to maximizing the efficiency of our available agricultural land through the deployment of drought tolerant cultivars. We studied the role of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 9 (SPL9), a target of miR156, in alfalfa’s (Medicago sativa) response to drought . We found SPL9 affects alfalfa’s phenotype and abiotic stress response by regulating the biosynthesis of anthocyanins. Transgenic alfalfa plants with RNAi-silenced SPL9(SPL9-RNAi) have decreased height, increased branching and decreased average internode length. In response to 12 days of withholding water, SPL9-RNAi plants show increased drought tolerance and decreased leaf senescence compared to wild-type (WT) plants. When comparing well-watered control and drought conditions, SPL9-RNAi plants show no decreases in fresh weight of above-ground tissue that is otherwise observed in WT plants. SPL9-RNAi plants are also better able to continue normal growth under drought stress. Significant differences in plant growth between control and stress conditions are not seen in SPL9-RNAi plants but are observed in WT plants. This study identifies SPL9 as a candidate molecular tool for improving alfalfa’s, and potentially other plants’ tolerance to drought stress.