Deciphering the ceRNA Network in Alfalfa: Insights into Cold Stress Tolerance Mechanisms.

Abiotic stress of cold is one of the limitation factors that hinder the production of alfalfa (Medicago sativa). Although there are a large number of studies suggesting that non-coding RNAs (ncRNAs) play an important role in plant response to abiotic stress, the mechanism by which ncRNAs and competing endogenous RNAs (ceRNAs) influence the low-temperature tolerance of alfalfa remains understudied. In this study, we integrated whole-transcriptome RNA-seq and genome-wide association studies (GWASs) to identify cold stress-related metabolic pathways and candidate genes, differentially expressed (DE) mRNAs, microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs). Degradome sequencing was used to verify the ceRNA network under cold stress. A total of 46,936 DEmRNAs were identified. Ribosome (ko03010), amino sugar and nucleotide sugar metabolism (ko00520), ribosome biogenesis in eukaryotes (ko03008), circadian rhythm-plant (ko00270), and starch and sucrose metabolism (ko00500) were the top five KEGG terms with the highest p-value, enriching the most number of DEmRNAs. MS.gene53818 (MsUAM1) was considered to be the critical candidate gene for alfalfa response to cold stress by conjoint analysis of GWASs and DEmRNAs. A total of 223 DEmiRNAs, 1852 DElncRNAs, and 13 DEcircRNAs were identified under cold stress. Functional analysis indicates that they play important roles in GO terms such as leaf development (GO:0048366), DNA-binding transcription factor activity (GO:0003700), central vacuole (GO:0042807), response to auxin (GO:0009733), and water channel activity (GO:0015250), as well as in KEGG pathways such as plant hormone signal transduction, starch and sucrose metabolism, and flavone and flavonol biosynthesis (ko00944). A ceRNA network comprising 28 DElncRNAs, 8 DEcircRNAs, 11 DEmiRNAs, and 23 DEmRNA triplets was constructed. In this study, mRNAs and ncRNAs were identified that may be involved in alfalfa's response to cold stress, and a ceRNA regulatory network related to cold stress was established, providing valuable genic resources for further research on the molecular mechanisms underlying alfalfa cold stress.