Doutoramento em Biologia
Functional characterization of putative effectors in pinewood nematode, Bursaphelenchus xylophilus
Maria Espada

Orientação:  Manuel Galvão de Melo e Mota & John T. Jones

Plant-parasitic nematodes cause huge economic and ecological losses in agriculture and forestryecosystems worldwide. The migratory endoparasitic nematode Bursaphelenchus xylophilus isunique in having phytoparasitic and mycetophagous phases in its life cycle. During thephytoparasitic stage, the nematode migrates within pine trees feeding on the contents of cortexand xylem parenchymal cells. Interactions of the nematode with the plant host are mediated byeffectors - secreted proteins originating from the pharyngeal gland cells. The main objective ofthis work was to identify and characterise nematode effector genes that play key roles inparasitism.Next-generation sequencing and bioinformatic analysis were used as a neutral approach toidentify novel effectors. The transcriptome of B. xylophilus has been sequenced to compare geneexpression in the mycetophagous and plant-parasitic stages to identify genes and morphologicaladaptions involved in plant parasitism. Additionally, transcripts from pharyngeal gland cells weresequenced. Analysis of the data revealed new parasitism-related proteins. A promoter DNAsequence motif was identified that is associated with expression in the pharyngeal gland cells,and was used to predict further effector sequences. A panel of 118 predicted effector genes witha signal peptide, at least one occurrence of the motif and that are upregulated in planta wereidentified.Functional data suggest that effectors are one key part of a multi-layered detoxification strategydeployed by B. xylophilus in order to protect itself from host defence responses. B. xylophilussecretes detoxification enzymes into the host, while simultaneously upregulating otherdetoxification enzymes within its digestive system. We showed that one of these enzymes – aglutathione S-transferase - has a protective activity against defence compounds produced by thehost. These data represent the most comprehensive analysis of novel effectors from thisnematode to date.