Characterization of SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL), and its role in drought stress tolerance in Medicago sativa (alfalfa).

Traditional breeding involving Medicago sativa (alfalfa), has resulted in minimal yield increases. Moreover, extreme environmental conditions threaten to further limit production. Strategies that make use of molecular tools – such as small non-coding RNA, miR156 – represent an innovative means by which to influence tolerance to abiotic stress. miR156 functions, at least in part, through the SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) family of transcription factors. In this study, the role of SPL9 in regulating alfalfa development and drought tolerance is evaluated. Examination of alfalfa plants with RNAi-mediated SPL9 (SPL9-RNAi) showed that plant height, stem thickness, and internode length are positively regulated by SPL9, whereas shoot branching is negatively regulated. SPL9-RNAi alfalfa also had enhanced tolerance to drought mediated by elevated anthocyanin content and expression of DIHYDROFLAVONOL 4-REDUCTASE (DFR), an enzyme involved in anthocyanin biosynthesis. Thus, manipulation of SPL9-mediated downregulation of DFR may represent one strategy to improve drought tolerance in alfalfa