The Mexican bean beetle (Epilachna varivestis) regurgitome and insights into beetle-borne virus specificity.

For nearly 400 million years, insects and plants have been embattled in an evolutionary arms race. Insects have developed diverse feeding strategies and behaviors in an effort to circumvent and overcome an extensive collection of plant defense tactics. Sap-sucking insects often inject saliva into hosts plants, which contains a suite of effector proteins and even microbial communities that can alter the plant's defenses. Lacking salivary glands, leaf-feeding beetles represent an interesting group of phytophagous insects. Feeding beetles regurgitate onto leaf surfaces and it is thought that these oral secretions influence insect-plant interactions and even play a role in virus-vector specificity. Since the molecular and biological makeup of the regurgitant is virtually unknown, we carried out RNA sequencing and 16S rDNA analysis on a major soybean pest, Epilachna varivestis, to generate the first ever beetle "regurgitome" and characterize its microbiome. Interestingly, the regurgitant is comprised of a rich molecular assortment of genes encoding putative extracellular proteins involved in digestion, molting, immune defense, and detoxification. By carrying out plant inoculation assays, we reinforced the fundamental role of the regurgitant in beetle-borne virus specificity. Ultimately, these studies begin to characterize the importance of regurgitant in virus transmission and beetle-plant interactions.

Genetic mapping and haplotype analysis of a locus for quantitative resistance to Fusarium graminearum in soybean accession PI 567516C.

KEY MESSAGE: A major novel quantitative disease resistance locus, qRfg_Gm06, for Fusarium graminearum was genetically mapped to chromosome 6. Genomic-assisted haplotype analysis within this region identified three putative candidate genes. Fusarium graminearum causes seed, root rot, and seedling damping-off in soybean which contributes to reduced stands and yield. A cultivar Magellan and PI 567516C were identified with low and high levels of partial resistance to F. graminearum, respectively. Quantitative disease resistance loci (QDRL) were mapped with 241 F7:8 recombinant inbred lines (RILs) derived from a cross of Magellan × PI 567516C. Phenotypic evaluation for resistance to F. graminearum used the rolled towel assay in a randomized incomplete block design. The genetic map was constructed from 927 polymorphic single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) markers. One major QDRL qRfg_Gm06 was detected and mapped to chromosome 6 with a LOD score of 20.3 explaining 40.2% of the total phenotypic variation. This QDRL was mapped to a ~400 kb genomic region of the Williams 82 reference genome. Genome mining of this region identified 14 putative candidate disease resistance genes. Haplotype analysis of this locus using whole genome re-sequencing (WGRS) of 106 diverse soybean lines narrowed the list to three genes. A SNP genotyping Kompetitive allele-specific PCR (KASP) assay was designed for one of the genes and was validated in a subset of the RILs and all 106 diverse lines.