Buffalograss defense response to Blissus occiduus feeding, chinch bug salivary gland morphology and the role of saliva in mediating plant-insect interactions

This research investigated the role of oxidative enzymes in the defense response of buffalograss, Buchloë dactyloides (Nuttall) Engelmann to the western chinch bug, Blissus occiduus Barber, increased the genomic resources available for buffalograss and investigated the salivary glands and associated salivary proteome of B. occiduus. Gene expression of four defense-related buffalograss transcripts (two peroxidases, a catalase, and a GRAS (gibberellic acid insensitive [GAI], repressor of GAI, and scarecrow) and total peroxidase activity were evaluated in response to chinch bug feeding in susceptible and tolerant buffalograsses. Basal levels of all four transcripts were consistently higher in the tolerant buffalograss when compared with the susceptible genotype. The four defense-related transcripts also exhibited differential expression between infested and control plants for both the tolerant and susceptible buffalograsses. Differences in total peroxidase activity were detected between control and infested plants, and basal peroxidase activity was higher in the tolerant genotype. Next generation sequencing examined the transcriptomes of tolerant and susceptible buffalograsses in response to chinch bug feeding. Sequence descriptions and gene ontology terms were assigned to over 1,600 differentially expressed genes. Several specific defense-related transcripts were differentially expressed and were described within the tolerant and susceptible buffalograsses. Seven peroxidase transcripts had higher basal expression levels in tolerant plants than in their susceptible counterparts. Comparison of control and infested transcriptomic data and subsequent comparisons of tolerant and susceptible genotypes revealed genes with significant levels of change, but observed only in the tolerant genotype. Finally, the salivary glands of B. occiduus were investigated to determine the overall structure and their potential functions. Light and scanning electron microscopy revealed a pair of tri-lobed principal glands and a pair of tubular accessory glands of differing cellular types. To link structure with function, the salivary gland proteome was characterized using liquid chromatography tandem mass spectrometry. A number of sequences were assigned the molecular function of hydrolase and oxido-reductase activity, with one specific protein sequence revealing a peroxidase-like molecular function. Understanding buffalograss tolerance mechanisms coupled with a better understanding of chinch bug salivary gland structure and function will provide valuable insights into the biological pathways impacted by buffalograss-chinch bug interactions