Sedentary endoparasitic phytonematodes are a group of taxa comprised of cyst nematodes (Heterodera and Globodera spp.) and root-knot nematodes (Meloidogyne spp. ), which are some of the most economically important crop pathogens on earth. These pests infect plant roots by creating elaborate feeding sites around the vasculature, which diverts nutrients away from the plant to feed the nematode and causes yield reduction in the plant. The nematodes create their feeding sites by delivering effector proteins into plant tissues. Effectors interact with plant components to modify development, metabolism, and defense pathways within plant cells, ultimately forming and maintaining the feeding site within the host root.

In order to find ways to mitigate the damages caused by these nematode pathogens, it is vital to identify nematode effectors and understand how effector proteins are able to manipulate the plant host. This dissertation first summarizes what is currently known about nematode effector proteins and then contributes to that body of knowledge. Our data show that two effectors from Heterodera schachtii (Hs4E02 and Hs25A01) are likely to function in the plant−nematode interaction by binding to plant proteins. Through the preparation and mining of gland transcripts we have also identified 18 additional putative effectors that are expressed specifically within the esophageal gland cells of Meloidogyne incognita during infective life stages. Two of these putative effectors are part of the major avirulence protein (MAP) family of effectors. Interestingly, we were able to identify conserved amino acid motifs within this effector family that resemble plant CLAVATA3/ESR (CLE) signaling peptides found in plants and cyst nematodes. These data indicate that the MAP effector family from root−knot nematodes may manipulate plant developmental signaling in a manner analogous to the CLE effectors secreted from cyst nematodes.