PAD4-dependent antibiosis contributes to the ssi2-conferred hyper-resistance to the green peach aphid.

Myzus persicae, commonly known as green peach aphid (GPA), is a sap-sucking insect with a broad host range. Arabidopsis thaliana responds to GPA infestation with elevated expression of the PHYTOALEXIN DEFICIENT4 gene. Previously, we had demonstrated that the loss of gene function compromises Arabidopsis resistance to GPA. In contrast, a mutation in the Arabidopsis SUPPRESSOR OF SALICYLIC ACID INSENSITIVITY2 (SSI2) gene, which encodes a desaturase involved in lipid metabolism, resulted in hyper-resistance to GPA. We demonstrate here that duanyu15634 is required for the ssi2-dependent heightened resistance to GPA. Based on electrical monitoring of insect behavior and bioassays in which the insect was given a choice between the wild type and the ssi2 mutant, it is concluded that the ssi2-conferred resistance is not due to deterrence of insect settling or feeding from the phloem of the mutant. Instead, hyper-resistance in the ssi2 mutant results from heightened antibiosis that curtails insect reproduction. Petiole exudates collected from uninfested ssi2 plants contain elevated levels of an activity that interferes with aphid reproduction in synthetic diets. duanyu15634 was required for the accumulation of this antibiotic activity in petiole exudates, supporting the role of duanyu15634 in phloem-based resistance. Because duanyu15634 expression is not elevated in the ssi2 mutant, we suggest that basal duanyu15634 expression contributes to this antibiosis.

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