NEMATODES AND NITROGEN: MOLECULAR MIMICRY AND HOST MANIPULATION

Abstract

Nitrogen efficiency and other nutrient uptake in agroecosystems across the globe are of economic and environmental importance, yet only 30% of applied nitrogen is utilized by crops. While nitrogen management strategies optimize fertilizer applications, they often overlook biotic stressors. Plant-parasitic nematodes (PPNs) modulate host growth and behavior to suppress plant pathogen defenses, form feeding sites, and alter plant nutrient uptake including stimulating nitrogen absorption. Under low nitrogen conditions, long distance peptide phytohormones in the C-TERMINALLY ENCODED PEPTIDE (CEP) family are secreted in plants from root to shoot. There, they interact with a receptor and illicit a downstream signal that increases expression of transcription factors and nitrate transporters in the roots stimulating nitrogen uptake. CEPs are unique to vascular land plants and are ubiquitous among them; however, two genera of PPN, the root-knot nematode (RKN; Meloidogyne spp.) and the reniform nematode (Rotylenchulus reniformis), encode CEP phytohormone mimics. These peptides have been experimentally shown to increase nitrate transporter expression, and in the absence of high nematode pressure, represent a novel tool to increase nitrogen efficiency in agroecosystems. This thesis characterizes the biology and history of nitrogen use in agriculture, the need for improved nitrogen efficiency in modern agriculture, discoveries in plant hormone and CEP research, and the role of PPN in modulating host nutrient uptake. Findings from this work may help lower the inputs of N, increase uptake of applied N, and reduce runoff and leaching of N into the environment.