A Role Of Auxin In Repression Of Harpin-Induced Hypersensitive Response In Tobacco

Most of harpin proteins can stimulate hypersensitive response on plants, but how plants regulate hypersensitive response cell death and what kinds of factors can affect harpin protein eliciting hypersensitive response are not clear by now. Indole-3-aceticacid (IAA) is the first natural auxin discovered and it participates and regulates many physiological activities in plants including defence responses against plant pathogen infection. So whether auxin has effect on harpin-induced hypersensitive response or not? if it is true, what is the molecular mechanism mediated by auxin?To uncover this issue, we used IAA as the reaserch obeject, established a method with which we can use high performance liquid chromatography to determine the content of IAA in tobacco and cotton. The study can fast separation and quantitative determination of the content of IAA in leaves of tobacco and cotton.The method is feasible and reliable.Transgenic tobacco expressing harpinxoo displayed increased level of IAA during 0-6 h after inoculation with TMV, while the IAA content in the nontransgenic tobacco decreased under the same treatment.Purified harpinxoo can induce hypersensitive reaction on tobacco leaves and 10-4 mol/L IAA can inhibit the induction of HR by harpin protein which can be reversed by applying 500μM 2,3,5-trllodobenzolc acid (TIBA) at the same time.Semiquantitive PCR was employed to detect expression of hypersensitive response marker gene hsr203J, disease defense gene chia5, nitrate reductase gene nr, and the genes of ChtA, ChtB, GluA, GluB, et al. during the process of HR. Gene nr not hsr203J and chia5 had constitutive expression in the wild tobacco leave. Applying of 10-4 mol/L IAA or 500μM TIBA respectively had no effect on expression status of the tested genes. Purified harpin induced the expression of hsr203J and chia5 but inhibit the expression of gene nr. The combined applification of 10-4 mol/L IAA and harpin protein, increased the expression of gene hsr203J but lowered the expression of gene chia5. Treatment with 500μM TIBA which reverse the HR inhibition by IAA changed the expression statement of gene chia5.To summarize, auxin can reverse the hypersensitive response stimulated by purified harpin protein to some extent. Gene hsr203J,chia5,nr had been involved in related metabolism ways in the interaction of 10-4mol/L IAA and harpin protein, but not the other genes. The results lay a foundation for us to study further more about the molecular mechanism of auxin affecting Harpin induced hypersensitive reaction.