Fig. 1 Chromosome distribution of SMXL gene family in M. truncatulaRed indicates high gene density, and blue indicates low gene density

Fig. 2 Phylogenetic tree of SMXL gene familyA: Interspecific phylogenetic tree. B: Intraspecific phylogenetic tree

Fig. 3 Conserved motifs, protein conserved domains, and gene structure of MtSMXLs in M. truncatulaA: Conserved motif of MtSMXL protein, different squares indicate different motif. B: MtSMXL protein domain, different squares indicate different protein domains. C: Gene structure of MtSMXL genes

Fig. 4 Cis-acting elements in the promoter of the SMXL genesA: Distribution of cis-acting element in the promoter region of the MtSMXL gene, with different colored ovals representing different cis-elements. B: Heatmap of the number of cis-acting elements in the promoter region of M . C: Stacked statistical chart of various cis-acting elements in the promoter region of the MtSMXL gene. Due to the overlap of promoter positions and space limitations, light-responsive elements and some growth- and development-related elements irrelevant to this study are not shown in the promoter position map A and the heatmap B

Fig. 5 Intraspecific collinearity of the MtSMXL genesThe gray lines indicate collinearity gene pairs in the genome, and the green lines indicate gene pairs ofcollinear MtSMXL. The inner and middle circles indicate the gene density of the M. truncatula genome, and the outermost circle indicates the chromosomes. The legend indicates the gene density in the inner circle, where yellow shows high gene density and blue shows low gene density

Fig. 6 Collinearity analysis of SMXL genes between M. truncatula and other speciesA: Collinearity analysis of SMXL family genes in M. truncatula, Glycine max and common bean. B: Collinearity analysis of SMXL family genes in M. truncatula, Z. mays and Arabidopsis. The collinear regions in the genomes of M. truncatula and other species are shown by gray lines, and the collinear SMXL gene pairs with other species are highlighted by bright lines

Fig. 7 Putative network for MtSMXLs interacting proteins M. truncatula

Fig. 8 Expression analysis of SMXL family genes indifferent tissues of M. truncatulaThe upper right corner shows the expression range of the MtSMXL gene in different tissues. Darker red indicates higher expression， and darker blue indicates lower expression. In the figure， adj refers to distance， and dap refers to days after pollination

Fig. 9 Expression analysis of SMXL family genes of M. truncatula under conditions of N, P, K and S deficiencyA: Heatmap of the expressions of MtSMXLs genes in response to low potassium treatment in the roots and shoots. B: Heatmap of the expressions of MtSMXLs genes in response to low nitrogen treatment in the roots and shoots. C: Heatmap of the expressions of MtSMXLs genes in response to low phosphorus treatment in the roots and shoots. D: Heatmap of the expressions of MtSMXLs gene in response to low sulfur treatment in the roots and shoots

Fig. 10 Gene expression analysis of candidate genes encoding interacting proteins under N, P, K and S treatmentsBased on GraphPad Prism 5.0 analysis, *P<0.05, **P<0.005

Fig. 11 Gene expression analysis of candidate genes encoding interacting proteins under drought, cold and salt treatment conditions

Fig. 12 Analysis of the gene expression patterns of SMXL family genes under drought, cold and salt treatmentA: Heatmap of the expression levels of MtSMXLs gene under drought treatment in seedlings. B: Heatmap of the expression levels of MtSMXLs gene under cold treatment in seedlings. C: Heatmap of the expression levels of MtSMXLs gene under salt treatment in seedlings