Genome-Wide Identification and Expression Analysis of the Cyclic Nucleotide-Gated Channel Gene Family in Zoysia japonica under Salt Stress

Salt stress severely inhibits plant growth. Understanding the mechanism of plant salt tolerance is highly important to improving plant salt tolerance. Previous studies have shown that nonselective cyclic nucleotide-gated ion channels (<i>CNGCs</i>) play an important role in plant salt tolerance. However, current research on <i>CNGCs</i> mainly focuses on <i>CNGCs</i> in glycophytic plants, and research on <i>CNGCs</i> in halophytes that exhibit special salt tolerance strategies is still scarce. This study used the halophilic plant <i>Zoysia japonica</i>, an excellent warm-season turfgrass, as the experimental material. Through bioinformatics analysis, 18 members of the <i>CNGC</i> family were identified in <i>Zoysia japonica</i>; they were designated <i>ZjCNGC1</i> through <i>ZjCNGC18</i> according to their scaffold-level chromosomal positions. <i>ZjCNGCs</i> are divided into four groups (I-IV), with the same groups having differentiated protein-conserved domains and gene structures. <i>ZjCNGCs</i> are unevenly distributed on 16 scaffold-level chromosomes. Compared with other species, the <i>ZjCNGCs</i> in Group III exhibit obvious gene expansion, mainly due to duplication of gene segments. The collinearity between <i>ZjCNGCs</i>, <i>OsCNGCs</i>, and <i>SjCNGCs</i> suggests that <i>CNGCs</i> are evolutionarily conserved among gramineous plants. However, the Group III <i>ZjCNGCs</i> are only partially collinear with <i>OsCNGCs</i> and <i>SjCNGCs</i>, implying that the expansion of Group III <i>ZjCNGC</i> genes may have been an independent event occurring in <i>Zoysia japonica</i>. Protein interaction prediction revealed that ZjCNGCs, calcium-dependent protein kinase, H⁺-ATPase, outwardly rectifying potassium channel protein, and polyubiquitin 3 interact with ZjCNGCs. Multiple stress response regulatory elements, including those involved in salt stress, are present on the <i>ZjCNGC</i> promoter. The qPCR results revealed differences in the expression patterns of <i>ZjCNGCs</i> in different parts of the plant. Under salt stress conditions, the expression of <i>ZjCNGCs</i> was significantly upregulated in roots and leaves, with <i>ZjCNGC8</i> and <i>ZjCNGC13</i> showing the greatest increase in expression in the roots. These results collectively suggest that <i>ZjCNGCs</i> play an important role in salt tolerance and that their expansion into Group III may be a special mechanism underlying the salt tolerance of <i>Zoysia japonica</i>.