INFLUENCE OF PLANT ELICITOR PEPTIDES ON PLANT DEFENSE, PLANT FITNESS, AND PRODUCTIVITY

The U.S. is the world's leading soybean producer, with ~80 million acres planted to soybean in 2019; after corn, it is the second most widely-grown crop in the US, valued at nearly $35 billion annually. Based on data from 1996 to 2016, economic losses to soybean diseases in the U.S. are estimated to exceed $4.5 billion/year, and the majority of these losses are due to soil-borne diseases such asnematodes, charcoal rot, and other seedling diseases. Of the soil-borne diseases that impact soybean, many impact other crops as well; most notably, root-knot nematodes (Meloidogynespp.)can infect hundreds of crops, and is among the most common and damaging crop pests world-wide. In fact, root-knot nematodes (RKN) were recently ranked number one in importance among the phytoparasitic nematodes.The goal of this project is to develop methods to activate broad-spectrum defenses in soybean that can reduce infection by nematodesand other soil-borne pathogens. We have chosen to focus on a class of defense activators called Plant Elicitor Peptides (PEPs) because they activate multiple defensive pathways and are found in a diverse array of plant species; thus,we hope to identify management strategies that would be active against multiple soil-borne pathogens on soybean including RKN, and that could in the futue also be applied to manage soil-borne diseases on other crops.PEPsare generated in response to damage through cleavage of propeptides (PROPEPs), and they induce defenses against diverse pathogens. In addition, PEPs may influence plant development, possibly contributing to tolerance. We have recently shown that PEP seed treatments reduce root-knot nematode (RKN) and soybean cyst nematode (SCN) infections on soybean, and that PROPEP overexpression may protect soybean and Arabidopsis against nematodes. In addition, we have found that the beneficial rhizobacterium Bacillus subtilis can be engineered to deliver PEPs and reduce RKN infection on potato. We propose to charcterize the benefits of propeptide overexpression, PEP seed treatments, and bacterially-delivered PEPs for management of nematodes and other soil-borne diseases in soybean, and to explore the impacts of these approaches on plant growth and productivity.Our specific objectives are to:Develop multiple tools to activate PEP-mediated immunity in crops, and compare their efficacy for nematode suppression. Specifically, we will characterize transgenic soybean lines with enhanced expression of a soybean propeptide (GmPROPEP3), develop a bacterial system for synthesizing the mature peptide (GmPEP3) in vitro,optimize methods for applyingpeptide seed treatments to soybean, and compare the nematode-suppressive effects ofseed treatmentsand transgenic lines.Characterize the impacts of activatingPEP-mediated immunity on soil-borne microbes of importance to plant health, including the severity of common soybean diseases, andthe balance of beneficial and pathogenic microbial guilds in these communities.Measure the costs and benefits of activatingPEP-mediated immunity on plant growth and productivity by examing the effects of PEPs on root growth, and on plant growth and yields in the presence and absence of nematode pressure.