Wenling Medic (Medicago polymorpha) is common in southern China and has long been utilized as a vegetable in eastern China, as well as a significant raw ingredient for livestock and pickled meals. As a legume, there is still a research vacuum, and the first problem Wenling Medic faces in production is the problem of seed germination. The germination percentage of Wenling Medic was low, according to production practice and laboratory tests performed in this work. Furthermore, after more than two years of storage, the germination percentage of Wenling Medic dropped sharply, and it lacked a long enough seed life. An attempt was made to restore the viability of the seeds using the polyethylene glycol (PEG) osmoregulation-mediated priming method, after the physiological and biochemical characteristics of the seeds were assessed using the anthrone method, Bradford assay, 3,5-dinitrosalicylic acid (DNS) method, and thiobarbituric acid (TBA) method. The findings showed that it has a relatively short storage age and, with a useable life of only two years under normal aging circumstances, is not deactivated soon after harvesting. In addition, whereas protein content and α-amylase concentration did not significantly correlate (p > 0.05) with storage life, the conductivity of exudate, malondialdehyde content, and carbohydrate content did (p < 0.05). The seed viability was not considerably increased by the saturation initiation mediated by osmoregulation, utilizing PEG. In conclusion, the decrease in Wenling Medic seeds’ germination ability was substantially connected with higher levels of lipid peroxidation and decreased carbohydrate levels, but not with protein concentrations or α-amylase activity. The timing of dehydration may need to be carefully controlled when using PEG osmoregulation to prime Wenling Medic seeds.

The Dof transcription factor is a plant-specific transcription gene family that plays various biological functions in plant development and stress response. However, no relevant research has been conducted on Medicago polymorpha. Here, 36 MpDof genes were identified in the M. polymorpha genome and further divided into 10 groups based on the comparative phylogenetic analysis. The essential information of MpDof genes, such as chromosomal localization, gene structure, conserved motifs, and selective pressures were systematically analyzed. All 36 MpDof genes were predicted to contain more cis-acting elements related to hormone response. MpDof24 and MpDof25 were predicted to interact with MpDof11 and MpDof26 to involve in the photoperiod blooms process. The MpDof genes showed a diverse expression pattern in different tissues. Notably, MpDof29 and MpDof31 were specifically expressed in the large pod and root, respectively, suggesting their crucial role in the pod and root development. qRT-PCR analysis indicated that the expression levels of MpDof10, MpDof25, MpDof26, and MpDof29 were obviously up-regulated under drought, salt, and cold stress. Collectively, genome-wide identification, evolutionary, and expression analysis of the Dof transcription gene family in M. polymorpha will provide new information to further understand and utilize the function of these Dof genes in Medicago plants.

SWEET (Sugars will eventually be exported transporter) proteins are a group of sugar transporters that are involved in sugar efflux, phloem loading, reproductive development, plant senescence, and stress responses. In this study, 23 SWEET transporter members were identified in the Medicago polymorpha genome, heterogeneously distributed on seven chromosomes. These MpSWEET genes were divided into four subfamilies, which showed similar gene structure and motif composition within the same subfamily. Seventeen MpSWEET genes encode seven transmembrane helices (TMHs), and all MpSWEET proteins possess conserved membrane domains and putative serine phosphorylation sites. Four and three pairs of MpSWEET genes were predicted to be segmentally and tandemly duplicated, respectively, which may have contributed to their evolution of M. polymorpha. The results of microarray and RNA-Seq data showed that some MpSWEET genes were specifically expressed in disparate developmental stages (including seedling stage, early flowering stage, and late flowering stage) or tissues such as flower and large pod. Based on protein network interaction and expression patterns of MpSWEET genes, six MpSWEET genes were selected for further quantitative real-time PCR validation in different stress treatments. qRT-PCR results showed that MpSWEET05, MpSWEET07, MpSWEET12, MpSWEET15, and MpSWEET21 were significantly upregulated for at least two of the three abiotic stress treatments. These findings provide new insights into the complex transcriptional regulation of MpSWEET genes, which facilitates future research to elucidate the function of MpSWEET genes in M. polymorpha and other legume crops.