Por Célia Miguel (BioISI, Ciências ULisboa).

Pine wilt disease (PWD), caused by the parasitic pinewood nematode (PWN), is a serious threat to conifer forests in Europe and Asia. Maritime pine (Pinus pinaster) is one of the most affected species due to its high susceptibility. However, heritable resistance has been reported in P. pinaster trees, opening the possibility for selecting and breeding for this trait. To uncover the mechanisms underlying resistance, we have analysed the transcriptional responses after inoculation with PWN in plants showing resistant and susceptible phenotypes. Our analysis revealed a strong reprograming of gene expression, particularly in resistant plants. Differential gene expression analysis highlighting roles for lignin synthesis and jasmonic acid defence pathway in resistance phenotypes were confirmed by biochemical analyses of cell wall composition and hormone pathways. Additionally, secondary metabolism, oxidative stress response and resistance genes seem relevant to overcome PWD. From the over 100 microRNAs responsive to PWN inoculation, some had predicted targets associated to roles in plant defense. The hypothesis of trans-kingdom miRNA transfer and gene silencing was also explored and suggested a role both in PWN parasitism as in P. pinaster resistance to PWD. Our results provide novel insights into transcriptional and post-transcriptional regulatory mechanisms which may be useful for the development of new strategies to protect P. pinaster forests from PWD.

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