Alfalfa response to heat stress is modulated by microRNA156.

Heat stress and extreme temperatures negatively affect plant development by disrupting regular cellular and biochemical functions, ultimately leading to reduced crop production. Alfalfa (Medicago sativa) is an important forage crop grown worldwide as forage for livestock feed. Limiting the effects of abiotic stress by developing alfalfa cultivars that are stress tolerant would help mitigate losses to crop production. Members of the microRNA156 (miR156) family regulate the Squamosa Promoter-Binding Protein-Like (SPL) genes that in turn impact plant growth and development by regulating downstream genes in response to various abiotic stresses. In this study, alfalfa with miR156 overexpression and SPL13 RNAi knockdown show increased tolerance to heat stress (40 degrees C). Transgenic plants show high water potential and increased non-enzymatic antioxidant content under heat stress. Moreover, anthocyanin content and chlorophyll abundance were increased under stress. Expression of some important transcription factors and downstream genes involved in abiotic stress response were altered in miR156-overexpressing genotypes under heat. Taken together, our results demonstrate that the miR156/SPL13 network contributes to improving heat stress tolerance in alfalfa.