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Root-Knot Nematode-Triggered Defense Responses in Arabidopsis thaliana During Early Stages of Parasitism


Root-knot nematodes (Meloidogyne spp., RKN) are plant parasites responsible for great losses in agriculture worldwide. After penetrating host roots they establish feeding sites by modifying a few cells from the pericycle, which become multinucleated and enlarged, known as giant cells. Classical nematology research focuses on the characterization of nematode effectors and plant resistance genes. Therefore, little is known about basal immunity against plant parasitic nematodes. In Chapter One we use Arabidopsis thaliana and M. incognita interaction as a model system to investigate plant perception of parasitic nematodes. We show that RKNs can be perceived by plants irrespective of possible damage caused during migration and this perception relies on canonical immunity signaling partners. In addition, we show that RKN perception by Arabidopsis is mediated by BAK1-dependent and independent pathways. To best characterize the transcriptional responses induced by RKN in Arabidopsis roots we performed RNAseq analysis, which is described in Chapter Two. RNAseq analysis revealed induction of several genes 24h after inoculation with RKN in both wild type plants and bak1-5 mutant roots. To identify candidate nematode receptors, RNAseq data was searched for genes that were upregulated upon RKN inoculation and encoded proteins with predicted membrane localization and kinase domains. Screening Arabidopsis with mutations on a few of these mutants allowed identification of a negative regulator of immunity against RKN that has elevated basal levels of defense marker genes and respond to elicitor treatment with stronger and faster ROS burst. Interestingly, this negative regulator belongs to a family of proteins that has not been extensively characterized, the G-type lectin receptor kinases (G-LecRKs). The Chapter Three shows an update on the characterization of Arabidopsis G-LecRKs as well as the first characterization of tomato G-LecRKs by using a methodology well established for characterization of other lectin receptor kinases family. Our analysis shows an expansion of G-LecRKs family in tomato as compared to Arabidopsis and organization of genes in clusters throughout each species genome. Motif enrichment analysis shows conservation of motifs among members of G-LecRKS of Arabidopsis as well as among members of Arabidopsis, tomato and the previously characterized rice G-LecRKs.

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