Heat shock transcription factors (HSFs) are important regulatory factors in plant stress responses to various biotic and abiotic stresses and play important roles in growth and development. The HSF gene family has been systematically identified and analyzed in many plants but it is not in the tetraploid alfalfa genome. We detected 104 HSF genes (MsHSFs) in the tetraploid alfalfa genome (“Xinjiangdaye” reference genome) and classified them into three subgroups: 68 in HSFA, 35 in HSFB and 1 in HSFC subgroups. Basic bioinformatics analysis, including genome location, protein sequence length, protein molecular weight and conserved motif identification, was conducted. Gene expression analysis revealed tissue-specific expression for 13 MsHSFs and tissue-wide expression for 28 MsHSFs. Based on transcriptomic data analysis, 21, 11 and 27 MsHSFs responded to drought stress, cold stress and salt stress, respectively, with seven responding to all three. According to RT–PCR, MsHSF27/33 expression gradually increased with cold, salt and drought stress condition duration; MsHSF6 expression increased over time under salt and drought stress conditions but decreased under cold stress. Our results provide key information for further functional analysis of MsHSFs and for genetic improvement of stress resistance in alfalfa.
The PLATZ family is a novel class of plant-specific zinc finger transcription factors with important roles in plant growth and development and abiotic stress responses. PLATZ members have been identified in many plants, including Oryza sativa, Zea mays, Triticum aestivum, Fagopyrum tataricum, and Arabidopsis thaliana; however, due to the complexity of the alfalfa reference genome, the members of the PLATZ gene family in alfalfa (Medicago sativa L.) have not been systematically identified and analyzed. In this study, 55 Medicago sativa PLATZ genes (MsPLATZs) were identified in the alfalfa “Xinjiangdaye” reference genome. Basic bioinformatic analysis was performed, including the characterization of sequence lengths, protein molecular weights, genomic positions, and conserved motifs. Expression analysis reveals that 7 MsPLATZs are tissue-specifically expressed, and 10 MsPLATZs are expressed in all examined tissues. The transcriptomic expression of these genes is obvious, indicating that these MsPLATZs have different functions in the growth and development of alfalfa. Based on transcriptome data analysis and real-time quantitative PCR (RT‒qPCR), we identified 22, 22, and 21 MsPLATZ genes that responded to salt, cold, and drought stress, respectively, with 20 MsPLATZs responding to all three stresses. This study lays a foundation for further exploring the functions of MsPLATZs, and provides ideas for the improvement of alfalfa varieties and germplasm innovation.
Alfalfa growth and production in China are negatively impacted by high salt concentrations in soils, especially in regions with limited water supplies. Few reliable genetic markers are currently available for salt tolerance selection. As a result, molecular breeding strategies targeting alfalfa are hindered. Therefore, with the continuous increase in soil salinity in agricultural lands, it is indispensable that a salt-tolerant variety of alfalfa is produced. We collected 220 alfalfa varieties around the world for resequencing and performed genome-wide association studies (GWASs). Alfalfa seeds were germinated in saline water with different concentrations of NaCl, and the phenotypic differences in several key root traits were recorded. In the phenotypic analysis, the breeding status and geographical origin strongly affected the salt tolerance of alfalfa. Forty-nine markers were significantly associated with salt tolerance, and 103 candidate genes were identified based on linkage disequilibrium. A total of 2712 differentially expressed genes were upregulated and 3570 were downregulated based on transcriptomic analyses. Some candidate genes that affected root development in the seed germination stage were identified through the combination of GWASs and transcriptome analyses. These genes could be used for molecular breeding strategies to increase alfalfa’s salt tolerance and for further research on salt tolerance in general.
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