Identification of Family Members and Characterization of the Low-Temperature-Stress-Responsive Genes in Luffa ( L.).

The plant-specific WRKY transcription factor family members have diverse regulatory effects on the genes associated with many plant processes. Although the WRKY proteins in and other species have been thoroughly investigated, there has been relatively little research on the WRKY family in , which is one of the most widely grown vegetables in China. In this study, we performed a genome-wide analysis to identify genes, which were subsequently classified and examined in terms of their gene structures, chromosomal locations, promoter cis-acting elements, and responses to abiotic stress. A total of 62 genes (471-2238 bp) were identified and divided into three phylogenetic groups (I, II, and III), with group II further divided into five subgroups (IIa, IIb, IIc, IId, and IIe) in accordance with the classification in other plants. The genes were unevenly distributed across 13 chromosomes. The gene structure analysis indicated that the genes contained 0-11 introns (average of 4.4). Moreover, 20 motifs were detected in the LcWRKY proteins with conserved motifs among the different phylogenetic groups. Two subgroup IIc members (LcWRKY16 and LcWRKY31) contained the WRKY sequence variant WRKYGKK. Additionally, nine cis-acting elements related to diverse responses to environmental stimuli were identified in the promoters. The subcellular localization analysis indicated that three LcWRKY proteins (LcWRKY43, LcWRKY7, and LcWRKY23) are localized in the nucleus. The tissue-specific expression profiles reflected the diversity in expression. The RNA-seq data revealed the effects of low-temperature stress on expression. The cold-induced changes in expression were verified via a qRT-PCR analysis of 24 differentially expressed genes. Both and were highly responsive to the low-temperature treatment (approximately 110-fold increase in expression). Furthermore, the , , and expression levels increased by more than 25-fold under cold conditions. Our findings will help clarify the evolution of the luffa family while also providing valuable insights for future studies on WRKY functions.