Transcriptome-Wide Identification of Dark- and Salt-Induced Senescence-Related NAC Gene Family Members in Alfalfa

Leaves are a key forage part for livestock, and the aging of leaves affects forage biomass and quality. Preventing or delaying premature leaf senescence leads to an increase in pasture biomass accumulation and an improvement in alfalfa quality. NAC transcription factors have been reported to affect plant growth and abiotic stress responses. In this study, 48 <i>NAC</i> genes potentially associated with leaf senescence were identified in alfalfa under dark or salt stress conditions. A phylogenetic analysis divided <i>MsNACs</i> into six subgroups based on similar gene structure and conserved motif. These <i>MsNACs</i> were unevenly distributed in 26 alfalfa chromosomes. The results of the collinearity analysis show that all of the <i>MsNACs</i> were involved in gene duplication. Some <i>cis</i>-acting elements related to hormones and stress were screened in the 2-kb promoter regions of <i>MsNACs</i>. Nine of the <i>MsNAC</i> genes were subjected to qRT-PCR to quantify their expression and <i>Agrobacterium</i>-mediated transient expression to verify their functions. The results indicate that <i>Ms.gene031485, Ms.gene032313, Ms.gene08494,</i> and <i>Ms.gene77666</i> might be key <i>NAC</i> genes involved in alfalfa leaf senescence. Our findings extend the understanding of the regulatory function of <i>MsNACs</i> in leaf senescence.