Transcriptome Analysis Reveals the Vital Role of ABA Plays in Drought Tolerance of the ABA-Insensitive Alfalfa (Medicago sativa L.)

Drought stress severely affects alfalfa (Medicago sativa L.) growth and production. It is particularly important to analyze the key networks of drought in alfalfa through physiological and molecular levels. However, how to quickly screen drought-tolerant alfalfa germplasm and how to elucidate the molecular pathways of alfalfa responding to drought are less studied. In this study, based on our previous research, we further verified the association between the heritability of ABA sensitivity during seed germination and drought tolerance of plants and identified the key pathways of drought tolerance differences between ABA-sensitivity (S1-0) and -insensitivity (S1-50) plants via RNA-seq and analysis. The results showed that the sensitivity to ABA in alfalfa seeds can be inherited and that plants that are insensitive to ABA during germination show stronger drought tolerance. An analysis of the differentially expressed genes (DEGs) revealed that ABA biosynthesis and signaling, amino acid metabolism, LEA, and wax synthesis-related pathways may be the key pathways that can be used for drought tolerance improvement in alfalfa. DEGs such as NCED, PYR/PYL, and PP2C may contribute to drought tolerance in the S1-50 plant. The study further confirms that screening with ABA at the seed germination stage can select alfalfa lines with good drought tolerance, which provides a new theoretical basis for alfalfa drought tolerance breeding. The expression of the key genes of alfalfa in response to drought stress was also tested.