Involvement of the Octadecanoid Pathway in Bluegreen Aphid Resistance in Medicago truncatula

Abstract

Aphids are major insect pests of plants that feed directly from the phloem. We used the model legume Medicago truncatula Gaert. (barrel medic) to elucidate host resistance to aphids and identified a single dominant gene which confers resistance to Acyrthosiphon kondoi Shinji (bluegreen aphid). To understand how this gene conditions resistance to bluegreen aphid, transcription profiling of 23 defense-related genes representing various signaling pathways was undertaken using a pair of near-isogenic lines that are susceptible or resistant to bluegreen aphid. All salicylic acid- and ethylene-responsive genes tested were induced by bluegreen aphid in resistant and susceptible plants, although there were some differences in the magnitude and kinetics of the induction. In contrast, 10 of 13 genes associated with the octadecanoid pathway were induced exclusively in the resistant plants following bluegreen aphid infestation. These results are in contrast to plant-pathogen interactions where similar sets of defense genes typically are induced in compatible interactions, but to a lesser degree and later than in incompatible interactions. Treatment of susceptible plants with methyl jasmonate reduced bluegreen aphid infestation but not to the same levels as the resistant line. Together, these results strongly suggest that the octadecanoid pathway is important for this naturally derived aphid resistance trait.

The B-3 Ethylene Response Factor MtERF1-1 Mediates Resistance to a Subset of Root Pathogens inMedicago truncatulawithout Adversely Affecting Symbiosis with Rhizobia

“…The expression of PR10 was found to be responsive to exogenous ethylene, whereas PR1 was not (Supplemental Table S2). The salicylate-and ethylene-responsive b-1,3-glucanase BGL2 (Supplemental Table S2; Gao et al, 2007) was significantly induced in A17 but not in skl, suggesting a reliance on ethylene signaling for pathogen induction of this gene (Fig. 3C).…”

“…The typically salicylate-responsive Pathogenesis related10 (PR10; Gao et al, 2007) showed a significant induction in skl but not A17 following R. solani AG8 infection, whereas PR1 showed no significant changes in either genotype (Fig. 3, A and B).…”

“…3E; Supplemental Table S2), suggesting that its pathogen-induced expression may also be dependent on ethylene signaling. However, VSP, which is only induced by jasmonate (Gao et al, 2007) but not ethylene (Supplemental Table S1), was not significantly regulated by R. solani inoculation in A17. VSP was significantly regulated in skl following R. solani inoculation, indicating that the jasmonate pathway may be playing a more substantial role in regulating defense gene expression in the absence of ethylene signaling.…”

“…The model legume and important pasture crop in Australia, Medicago truncatula (barrel medic), has proven to be a valuable host for investigations of plant defense responses (Klingler et al, 2005;Colditz et al, 2007;Foster-Hartnett et al, 2007;Gao et al, 2007;Naoumkina et al, 2008;Pilet-Nayel et al, 2009). In this study, we investigate the molecular responses of M. truncatula to infection by R. solani AG8.…”

Transcriptomics of induced defense responses to greenbug aphid feeding in near isogenic wheat lines

“…The phytohormones SA, jasmonic acid (JA), and ethylene (ET) activate herbivore induced signals via independent, antagonistic, and synergistic pathways and interface with other hormones auxin, abscisic acid (ABA), brassinosteroid (BR), gibberellins (GA), and cytokinin (CK) [25][26][27][28]. Additionally, as part of the defense mechanisms against phloem-feeding insects and other herbivores, plants are known to alter secondary metabolites, glutathione S-transferases (GSTs), peroxidases, and redox homeostasis [19,[29][30][31].…”