Abstract
Stenotrophomonas maltophilia influences the reproduction, pathogenicity, and gene expression of aseptic Bursaphelenchus xylophilus after inoculation of aseptic Pinus massoniana. Pine wilt disease is a destructive pine forest disease caused by B. xylophilus, and its pathogenesis is unclear. The role of bacteria associated with B. xylophilus in pine wilt disease has attracted widespread attention. S. maltophilia is one of the most dominant bacteria in B. xylophilus, and its effect is ambiguous. This study aims to explore the role of S. maltophilia in pine wilt disease. The reproduction and virulence of aseptic B. xylophilus and B. xylophilus containing S. maltophilia were examined by inoculating aseptic P. massoniana seedlings. The gene expressions of two nematode treatments were identified by transcriptome sequencing. The reproduction and virulence of B. xylophilus containing S. maltophilia were stronger than that of aseptic nematodes. There were 4240 differentially expressed genes between aseptic B. xylophilus and B. xylophilus containing S. maltophilia after inoculation of aseptic P. massoniana, including 1147 upregulated genes and 2763 downregulated genes. These differentially expressed genes were significantly enriched in some immune-related gene ontology (GO) categories, such as membrane, transporter activity, metabolic processes, and many immune-related pathways, such as the wnt, rap1, PI3K-Akt, cAMP, cGMP-PKG, MAPK, ECM-receptor interaction, and calcium signaling pathways. The polyubiquitin-rich gene, leucine-rich repeat serine/threonine-protein kinase gene, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene, acetyl-CoA carboxylase gene, and heat shock protein genes were the key genes associated with immune resistance. Moreover, there were four cell wall hydrolase genes, thirty-six detoxification- and pathogenesis-related protein genes, one effector gene and ten cathepsin L-like cysteine proteinase genes that were differentially expressed. After inoculation of the host pine, S. maltophilia could affect the virulence and reproduction of B. xylophilus by regulating the expression of parasitic, immune, and pathogenicity genes of B. xylophilus.
Highlights
Pine wilt disease (PWD) is a devastating disease in pines caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus
At 3 dpi, thirteen P. massoniana seedlings inoculated with aseptic PWNs (Bx_a) began to lose water and turn brown; the infection rate was 54.17%, and the disease severity index (DSI) was 13.54
Twenty-one pine seedlings inoculated with the nematode with S. maltophilia (Bx_b) showed infection; the infection rate was 87.50%, and the DSI was 21.88
Summary
Pine wilt disease (PWD) is a devastating disease in pines caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus. It is native to North America [1], and epidemic in East Asian (China, Japan, and Korea) [2,3,4], causing serious ecological damage and economic loss. Since PWD was reported in 1982 in Nanjing, China, it has spread to 18 provinces with an area of more than 1.1 million hm , and more. Forests 2020, 11, 908 than 80 million pine trees have wilted completely [5]. The occurrence and development of the disease involve many factors, such as susceptible pine hosts, a beetle vector, the nematode, associated bacteria and fungi, and the appropriate geographical environment. A large number of bacteria can adhere to the surface of B. xylophilus, some of them are random [7,8,9]
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