Abstract
Pine wilt disease (PWD), caused by the plant–parasitic nematode Bursaphelenchus xylophilus, has become a severe environmental problem in the Iberian Peninsula with devastating effects in Pinus pinaster forests. Despite the high levels of this species' susceptibility, previous studies reported heritable resistance in P. pinaster trees. Understanding the basis of this resistance can be of extreme relevance for future programs aiming at reducing the disease impact on P. pinaster forests. In this study, we highlighted the mechanisms possibly involved in P. pinaster resistance to PWD, by comparing the transcriptional changes between resistant and susceptible plants after infection. Our analysis revealed a higher number of differentially expressed genes (DEGs) in resistant plants (1,916) when compared with susceptible plants (1,226). Resistance to PWN is mediated by the induction of the jasmonic acid (JA) defense pathway, secondary metabolism pathways, lignin synthesis, oxidative stress response genes, and resistance genes. Quantification of the acetyl bromide-soluble lignin confirmed a significant increase of cell wall lignification of stem tissues around the inoculation zone in resistant plants. In addition to less lignified cell walls, susceptibility to the pine wood nematode seems associated with the activation of the salicylic acid (SA) defense pathway at 72 hpi, as revealed by the higher SA levels in the tissues of susceptible plants. Cell wall reinforcement and hormone signaling mechanisms seem therefore essential for a resistance response.
Highlights
Pine wilt disease (PWD) is caused by Bursaphelenchus xylophilus, or pinewood nematode (PWN), which is transmitted by the insect vector Monochamus spp. while feeding on healthy trees
To identify genes that may be involved in resistance to PWD, an artificial PWN inoculation assay was performed with plants from a previously characterized half-sib family (Carrasquinho et al, 2018)
Combining differential gene expression analysis with hormone and lignin quantification, we identified pathways and mechanisms potentially involved in PWN resistance
Summary
Pine wilt disease (PWD) is caused by Bursaphelenchus xylophilus, or pinewood nematode (PWN), which is transmitted by the insect vector Monochamus spp. while feeding on healthy trees. In the Iberian Peninsula, it was first detected in the late 1990’s (Mota et al, 1999), spreading rapidly through Portugal and reaching Spain. In this region, it infects mostly Pinus pinaster trees, which are highly susceptible (Evans et al, 1996). Given the high economic and ecological value of P. pinaster in southwestern Europe due to its use in paper, wood, and resin production, its importance for soil protection, and as wildlife habitat, PWD has a huge impact on the local economy and environment (Webster and Mota, 2008; Vicente et al, 2012)
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