Metabolomics Differences of Glycine max QTLs Resistant to Soybean Looper.

Maryam Yousefi-Taemeh,Wayne Parrott,Nik Kovinich,Jie Lin,Demian R Ifa

doi:10.3390/metabo11100710

Abstract

Quantitative trait loci (QTLs) E and M are major soybean alleles that confer resistance to leaf-chewing insects, and are particularly effective in combination. Flavonoids and/or isoflavonoids are classes of plant secondary metabolites that previous studies agree are the causative agents of resistance of these QTLs. However, all previous studies have compared soybean genotypes that are of dissimilar genetic backgrounds, leaving it questionable what metabolites are a result of the QTL rather than the genetic background. Here, we conducted a non-targeted mass spectrometry approach without liquid chromatography to identify differences in metabolite levels among QTLs E, M, and both (EM) that were introgressed into the background of the susceptible variety Benning. Our results found that E and M mainly confer low-level, global differences in distinct sets of metabolites. The isoflavonoid daidzein was the only metabolite that demonstrated major increases, specifically in insect-treated M and EM. Interestingly, M confers increased daidzein levels in response to insect, whereas E restores M’s depleted daidzein levels in the absence of insect. Since daidzein levels do not parallel levels of resistance, our data suggest a novel mechanism that the QTLs confer resistance to insects by mediating changes in hundreds of metabolites, which would be difficult for the insect to evolve tolerance. Collective global metabolite differences conferred by E and M might explain the increased resistance of EM.

Highlights

The use of crop protectants and fertilizers has helped maintain crop productivity, but these have masked the fact that yield loss from insects continues to increase [1]
Soybean is a refuge for Bt corn and cotton in the United States, so Bt soybean cannot be commercialized in the USA without changes to Bt corn and cotton resistance management strategies
Principal component analysis (PCA) and orthogonal PLS-PA were unable to distinguish the genotypes or treatments based on the 13,950 unique peaks that were measured (Supplementary Figure S1)

Summary

Introduction

The use of crop protectants and fertilizers has helped maintain crop productivity, but these have masked the fact that yield loss from insects continues to increase [1]. In the case of soybean, freshwater ecotoxicity has tripled, largely due to increased insecticide application, ones that are more persistent in the soil and water [2]. Efforts to lower the cost of production, along with increased concerns over insecticide residues in the food chain and environment, underscore the need for insect-resistant crops [3]. Soybean is one of the crops that is affected by defoliating insects, in the Southeastern United States and in tropical South America. Even in South America where Bt soybean is used [5], pyramiding other resistance genes with Bt is needed to obtain a more durable resistance

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