Performing Department
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Non Technical Summary
Sweet potato is a highly nutritious crop with an annual US cultivation of over 3 billionpounds. Its different cultivars are rich in starch as well as micronutrients such as vitamins,minerals, carotenoids, flavonoids and anthocyanins, which make it very appealing as a staple crop,in various processed foods such as purees, juices, pies, cakes, noodles and chips, in the foodcolorant industry, as well as in health foods owing to its strong antioxidant potential. Its globalmarket thus is huge (est. >$40 billion), with the crop contributing ~$700 million to the US economy alone. Sweet potato is highly drought resistant and is known as a "crop that surviveswhen other crops fail", even surviving bouts of flooding that damage other crops. This climate resiliency makes sweet potato a centerpiece of hunger elimination and nutritional equality effortsglobally, adding to its value to humanity. However, this crop is threatened by various pests anddiseases such as weevils, wireworm, flea beetles, root rot nematodes as well as various fungi,bacteria and viruses, requiring heavy use of pesticides in major production areas. Due tochanging climate and species ranges of pests and pathogens, identifying how sweet potato can besustainably safeguarded against these biotic challenges is a critical challenge.In this research, we focus on a "hyper diverse" class of defense metabolites called resinglycosides (RGs) that are unique to sweet potato and its parent family Convolvulaceae (morningglories). This family contains many popular horticultural species as well as devastating weeds suchas bindweeds, all of which produce RGs. Substantial prior work, indigenous knowledge and ourpreliminary results suggest that RGs can be effective general deterrence against damage by insects,nematodes as well as fungi and viruses. Our recent workdefined substantial RG diversitywithin and between species, however, the biosynthetic pathway of RGs is completely unknown.Knowing the biosynthetic enzymes will not only open up new genetic targets for breeding of pest-resistant sweet potato varieties but also enable engineering of this trait in other crops such astomato. Our Preliminary Results have highlighted multiple enzyme candidates. In this research, we will (Obj. 1) assess the natural variation of resin glycosides in the USDA sweet potato germplasmcollection (Obj. 2) Identify additional RG biosynthetic candidate genes using RNA-seq and proteomics and (Obj. 3)Validate candidate genes in resin glycoside biosynthesis using functional genomics.Obtaining this foundational knowledgewill pave the way for molecular breeding and crop engineering. Wewill also share results of this research with major breeding centers in North Carolina, Louisianaand other states for translating the findings to the field.
Animal Health Component
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Research Effort Categories
Basic
100%
Applied
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Developmental
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Goals / Objectives
Sweet potato is among the top 10 most cultivated crops globally and is valuable for not just avariety of food products but also for hunger elimination efforts worldwide. Despite its yieldbeing affected by numerous pests and pathogens, its defense metabolites are poorly understood.Here we focus on a hyperdiverse class of its defense compounds called resin glycosides (RGs).Despite its vast structural diversity and known pesticidal/herbicidal activities, the core RGbiosynthetic enzymes are completely unknown. We recently developed metabolomic,computational and functional genomic tools to probe RG diversity and characterize itsbiosynthesis, which identified multiple candidate genes. In proposed research, we will (Objective1)apply these tools to survey 55 diverse accessions from the USDA sweet potato germplasmcollection and associate RG levels with their previously scored insect/nematode susceptibilities.(Objective2) To prioritize genes for functional validation, we will perform RNA-seq from high- andlow-RG cultivars as well as proteomics from sweet potato roots. (Objective3) Role of predictedcandidates in RG biosynthesis will be validated through in vitro and in vivo assays, including viapathway reconstruction in Nicotiana benthamiana. These experiments will identify high-RGlines for sweet potato breeding, generate hypotheses about RG relationship with pestsusceptibility, and enable reconstitution of this pathwayin other crops. Foundational knowledgeof this metabolite class with herbicidal/pesticidal activities will contribute to discoveries tosafeguard sweet potato and the long-term demand for sweet potato-based products.
Project Methods
Obj. 1: Assess the natural variation of resin glycosides in the USDA sweet potato germplasmcollectionUsing semi-targeted liquid chromatography mass spectrometry (LC-MS),we will assess the types and constitutive levels of RGs as well as other defense metabolites among55 accessions available in the USDA germplasm repository that have been previously scored fortheir insect/nematode sensitivity and population structure. This sampling will identify high- andlow- RG accessions, and associate RG levels to their previously known pest susceptibilities.Obj. 2: Identify additional RG biosynthetic candidate genes using RNA-seq and proteomicsUsing three high- and three low-RG accessions, we will identify candidate genes involved in RGbiosynthesis and transcriptional regulation using RNA-seq. RNA-seq in the RG-producing,horticulturally popular species Dichondra argentea Silver Falls and proteomics in sweet potatowill also assist identification of additional candidates.Obj. 3: Validate candidate genes in resin glycoside biosynthesis using functional genomicsOur Preliminary Results highlight multiple candidate RG enzymes, which - along with any otherenzymes identified from Obj. 2 - will be validated using enzyme assays and transientoverexpression/silencing in Ipomoeas, for which we have developed the technical foundation. These enzymes will further be over-expressed in low RG sweet potato accessions and throughpathway reconstruction in Nicotiana benthamiana to determine feasibility of expressing thischemical trait in other crop species.