Multiple Regulatory Networks Are Activated during Cold Stress in Medicago sativa L.

Abstract

Cultivated alfalfa (Medicago sativa L.) is one of the most important perennial legume forages in the world, and it has considerable potential as a valuable forage crop for livestock. However, the molecular mechanisms underlying alfalfa responses to cold stress are largely unknown. In this study, the transcriptome changes in alfalfa under cold stress at 4 °C for 2, 6, 24, and 48 h (three replicates for each time point) were analyzed using the high-throughput sequencing platform, BGISEQ-500, resulting in the identification of 50,809 annotated unigenes and 5283 differentially expressed genes (DEGs). Metabolic pathway enrichment analysis demonstrated that the DEGs were involved in carbohydrate metabolism, photosynthesis, plant hormone signal transduction, and the biosynthesis of amino acids. Moreover, the physiological changes of glutathione and proline content, catalase, and peroxidase activity were in accordance with dynamic transcript profiles of the relevant genes. Additionally, some transcription factors might play important roles in the alfalfa response to cold stress, as determined by the expression pattern of the related genes during 48 h of cold stress treatment. These findings provide valuable information for identifying and characterizing important components in the cold signaling network in alfalfa and enhancing the understanding of the molecular mechanisms underlying alfalfa responses to cold stress.

Differential expression analysis of genes in the root crown of alfalfa under low-temperature stress

“…This study indicated that the key enzyme in the ROS-scavenging systems in the Longmu 806 variety was upregulated as a defense to resist low-temperature stress, and the upregulation of the SOD1 gene may be a special protective mechanism in the Longmu 806 variety. The SOD1 gene may reduce the root freezing damage directly by increasing the superoxide scavenging capacity or indirectly by increasing the flux of H 2 O 2 [7], thereby maintaining a high survival rate of the alfalfa in severe winter conditions. The SOD1 may be one of the reasons why the Longmu 806 variety has a higher winter survival rate than the Sardi variety.…”

“…Plants can survive safely in winter and enhance freezing resistance through a low-temperature adaptation process [6]. Previous studies on the mechanisms of plant responses to low temperature have mainly focused on plant physiology, phytohormones, and changes in low temperature-induced gene expression by regulating transcription factors (TFs) [7]. Plants undergo various changes under low-temperature stress, and the key response to low-temperature stress depends on the activation of molecular networks involved in stress signal transduction pathways and the expression of specific sets of stress-related genes [8].…”

“…For example, with the introduction of a new generation of RNA-Seq, transcriptome sequencing technology has been used to identify lowtemperature stress response genes in Ipomoea batatas [33], Populus tomentosa [34], Capsicum annuum [35], and Magnolia wufengensis [36]. Moreover, some recent studies have reported that the use of transcriptome sequencing technology to analyze the expression of genes in the seedlings [7], taproots [37], and crown buds [38] of alfalfa, which provides valuable resources for functional genomics research on alfalfa cold tolerance. However, the understanding of genetic regulation information regarding low-temperature stress remains limited.…”

Different Genes Express Analysis of root crown of alfalfa under low temperature stress

“…Plants can survive safely in winter and enhance freezing resistance through low temperature adaptation process [9]. The study of plant low temperature adaptation mechanism mainly focuses on physiological, phytohormones, and transcription factor regulation of low temperature induced gene expression changes [10]. Plants adapt to various changes in low temperature stress, and the critical response to low temperature stress conditions depends on the activation of molecular networks involved in the expression and signaling of specific stress-related genes [11].…”

“…In addition, studies on differentially expressed genes of low temperature resistance of alfalfa varieties have also been reported. A recent study reported that transcriptome high-throughput sequencing technology has been used to analysis the expression of the gene of the seedling [10], taproots [41], and crown buds [42] of alfalfa, which provides valuable resources for functional genomics research on plant cold tolerance in the future. However, the understanding of genetic response information for low temperature stress was limited, since some of the previous studies only RNA-seq the seedling, taproots, and crown buds of alfalfa.…”