Modulation of defense-response gene expression in wheat during Hessian fly larval feeding

Abstract

Expression profiles of ten genes commonly up-regulated during plant defense against microbial pathogens were compared temporally during compatible and incompatible interactions with first-instar Hessian fly larvae, in two wheat lines carrying different resistance genes. Quantitative real-time PCR revealed that while a lipoxygenase gene (WCI-2 ) was strongly upregulated during the incompatible interactions, genes encoding b-1,3 endoglucanase (GNS ) and an integral membrane protein (WIR1 ) were moderately responsive. Genes for thionin-like protein (WCI-3 ), PR-17-like protein (WCI-5 ), MAP kinase (WCK-1 ), phenylalanine ammonia-lyase (PAL ), pathogenesis-related protein-1 (PR-1 ), receptor-like kinase (LRK10 ) and heat shock protein 70 (HSP70 ) were minimally responsive. The application of signaling molecules, salicylic acid (SA), methyl jasmonate (MJ) and abscisic acid (ABA), to insect-free plants demonstrated association of these genes with specific defense-response pathways. SA-induced up-regulation of a gene related to lipoxygenases that are involved in jasmonic acid (JA)-biosynthesis is suggestive of positive cross-talk between SA-and JA-mediated signaling pathways. Data suggest that alternative mechanisms may be involved since few of these classical defense-response genes are significantly upregulated during incompatible interactions between wheat and Hessian fly.

Antioxidant defense response in a galling insect

“…Two resistant wheat lines, P19346A1-2-5-5-2 and Iris (the line used in this study), carrying the Hessian fly resistance genes H13 and H9 increase expression of a LOX mRNA (WCI-2) in response to feeding first larval instar. WCI-2 is initially up-regulated in Iris wheat (2.5-fold compared with uninfested wheat plants) 6 h after hatching of Hessian fly larvae (22). Peak expression of WCI-2 (Ͼ30-fold) occurs 24 h after hatching in both resistant wheats participating in incompatible interactions.…”

“…H 2 O 2 can cause lipid peroxidation, which severely damages insect cells and thereby retards development (33). Recent evidence suggests that resistant wheat plants increase LOX in response to feeding Hessian fly larvae (22). LOX produces ROS including LOOH and H 2 O 2 as a by-product (32,34).…”

“…Resistant wheat undergoes little or no physiological stress during Hessian fly attack (21) and yields normally. Furthermore, resistant wheat in response to attack by larval Hessian fly has been shown to produce greater levels of mRNAs for a number of putative defense genes including lipoxygenase (LOX), an ROSgenerating enzyme (22).…”

Functional Characterization of HFR1, a High-MannoseN-Glycan-Specific Wheat Lectin Induced by Hessian Fly Larvae

“…In contrast to the rapid initiation of feeding by the virulent larvae, the avirulent larvae exhibited prolonged activity (Table II), as a gene-for-gene recognition event triggers increased mRNA levels of defense genes (Sardesai et al, 2005b) along with genes encoding lectins, such as Hfr-1 (Subramanyam et al, 2006) and Hfr-3 (Giovanini et al, 2007). The specific elicitation of these wheat lectins, which previously have not been linked to defense, suggests the targeted involvement of this class of proteins during resistance to Hessian fly.…”

“…However, it is now known that the mechanisms of plant defense in these interactions are very different. Classical pathogenesisrelated and other defense-response genes associated with plant-pathogen interactions are minimally responsive in resistant wheat during Hessian fly larval attack (Sardesai et al, 2005b). No evidence of a classical oxidative burst has been detected in wheat following attack by virulent or avirulent Hessian fly larvae (Giovanini et al, 2006).…”