Abstract:  【Aim】This study aims to investigate the chemotaxis and thermotaxis of Bursaphelenchus xylophilus, by analyzing the physicochemical properties, structure and functions of the members of TAX family and the expression of TAX family gene Bx-taxs after drug and low-temperature stresses. 【Methods】Based on the NCBI database, the TAX family gene sequences of Caenorhabditis elegans were retrieved and compared with B. xylophilus genome for tBlastn to search candidate TAX family genes in B. xylophilus. The candidate sequences were screened and cleaned by software and online tools such as ExPASy, WoLF PSORT, SOPMA, Alphafold 3, MEME, CD-Search and TBtools, and Bx-taxs of B. xylophilus were identified and the gene structure and chromosomal localization, and the subcellular localization, sequence features, physicochemical properties, secondary structure and tertiary structure of their proteins were analyzed. A phylogenetic tree of TAX protein sequences was constructed by IQtree software to infer phylogenetic relationships. The expression profiles of six Bx-taxs were analyzed to determine the roles of Bx-taxs by subjecting B. xylophilus to emamectin benzoate drug stress and low-temperature stress. 【Results】A total of six members of the TAX family, Bx-TAX-1-6, were identified from B. xylophilus. These proteins had 623-1 115 amino acid residues, relative molecular masses of 71.49-129.27 kD, and theoretical isoelectric points of 5.68-9.04, most of them being hydrophilic proteins. All six TAX family members were located on the cell membrane, especially the Bx-TAX-1 protein was also distributed in the cytoplasm. The secondary structures of the TAX family proteins were mainly composed of α-helixes and random coils, accounting for 42.10%-53.07% and 32.38%-45.80%, respectively. Chromosomal localization and phylogenetic analyses showed that TAX family genes of B. xylophilus were distributed on four chromosomes of which genes were closer to the TAX-4 genes of other nematodes, except for the Bx-TAX-1 gene, which was a separate branch. Under emamectin benzoate stress, all genes of the members of TAX family showed different degrees of down-regulation of expression within 12 h, and up-regulation of expression at 24 h. Among them, the expression levels of Bx-tax-3, Bx-tax-5 and Bx-tax-6 were up- or down-regulated by more than 1-fold. Only Bx-tax-5 was up-regulated under low-temperature stress, while the others were down-regulated. 【Conclusion】 TAX family genes of B. xylophilus show varying degrees of response to emamectin benzoate and low temperature stresses. The results of this study provide a theoretical basis for chemical and temperature tropism studies based on the TAX family, and provide a research basis for B. xylophilus response to chemical stress and its northward migration mechanism.

Key words: Bursaphelenchus xylophilus, TAX gene, gene family analysis, gene expression, gene function