Indole-3-acetic acid reverses the harpin-induced hypersensitive response and alters the expression of hypersensitive-response-related genes in tobacco

Harpin proteins stimulate hypersensitive response (HR) in plants. However, the mechanism by which HR is regulated is not clear. The role of the auxin, indole-3-acetic acid (IAA), in the control of harpin-stimulated HR was investigated. IAA was used to inhibit HR that was stimulated by purified fusion harpin_Xoo protein in tobacco. Semi-quantitative PCR and qRT-PCR were employed to detect the expression of HR related genes. IAA at 100 μM reversed harpin-induced HR which was inhibited by 500 μM 2,3,5-triiodobenzoic acid (TIBA). Semi-quantitative PCR and qRT-PCR showed the combined application of 100 μM IAA and harpin protein from Xanthomonas oryzae enhanced the expression of HR marker gene, hsr203J, but weakened the expression of the disease-defense gene, chia5. TIBA also decreased the expression of hsr203J but increased the expression of chia5. Thus, the auxin can reverse harpin_Xoo-induced HR.