On the molecular biology and evolution of plant parasitism by nematodes
Plant-parasitic nematodes (PPN) are among the most devastating plant pathogens. However, our understanding of how nematodes adapted to plant parasitism, and the molecular mechanisms that PPN use during infection is limited. Among the most important genomic changes that occurred in the free-living nematode ancestors of PPN were multiple horizontal gene transfer (HGT) events from bacteria. Though it is clear that HGT helped shape the genomes of many PPN, how this process occurred is unknown. Also, it is evident that successful parasitism occurs from the delivery of proteinaceous effectors into plant roots to hijack and modify host cellular processes. The research included in this dissertation aims at addressing several important questions regarding HGT in PPN, and investigates important molecular, cellular and developmental processes that are determined critical for successful parasitism. Of particular emphasis throughout this dissertation is the soybean cyst nematode, Heterodera glycines, due to a highly specialized and agronomically important interaction with its soybean host. Major findings for HGT in PPN include the identification of eighteen new H. glycines effectors, three of which are determined to have been part of more ancient HGT events from rhizosphere bacteria. Additionally, homologs of two of the three HGT genes are shown to have been transferred numerous different times from bacteria to diverse eukaryotes and archaea. The latter findings indicate the likely evolutionary advantages that these genes provided not just to PPN, but many different taxa. Intriguingly, we reveal that a group of retroviruses specific to distal nematode clades is genomically associated