Indole-3-acetic Acid Regulates The Harpin-induced Hypersensitive Response And The Expression Analysis Of Auxin Related Genes

Harpin proteins can stimulate hypersensitive response (HR) on plants, but now, how plants regulate the mechanism of hypersensitive response is not clear. 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. IAA may play a role in the plant defense. So what is the role IAA act as? And what is the molecular mechanism mediated by auxin?This paper consists of two parts. The first part researches whether IAA can repress the HR stimulated by harpin protein on tobacco leaves without coated with IAA directly. The second part researches whether IAA can repress the HR on tobacco leaves stimulated by Pseudomona syringae pv. tomato DC3000, Xanthomonas axonopodis pv. citri and chitosan.In the first part, the authors studied the issue from plant assays, oxidative burst of tobacco leaf tissues and semi-quantitative PCR. The EF-1a gene was used as an internal control because it is highly conserved and constitutively expressed in eukaryotes. Plant assays showed that10-4mol/L IAA can reverse the HR stimulated by harpinxoo protein on tobacco leaves without coated with IAA directly, and the effect can be inhibited by applying500μM2,3,5-trllodobenzolc acid (TIBA) at the same time. Then we determined the condition of oxidative burst of tobacco leaf tissues. The results were in accordance with the results of plant assays that IAA could reduce the accumulation of ROS. The results of semi-quantitative PCR showed that IAA had different effects on the expressions of hypersensitive response marker gene hsr203J, disease defense gene chia5and PR-1b, auxin related.genes AUX1、ARF8and so on. To conclude, auxin can reverse the hypersensitive response stimulated by harpinxoo protein on tobacco leaves without coated with IAA directly.In the second part, the authors studied whether10-4mol/L IAA can reverse the HR stimulated by Pseudomona syringae pv. tomato DC3000, Xanthomonas axonopodis pv. citri and lmg/ml chitosan on tobacco leaves. Then the authors studied the issue from oxidative burst of tobacco leaf tissues and semi-quantitative PCR. Plant assays showed that10-4mol/L IAA can reverse the HR stimulated by Pseudomona syringae pv. tomato DC3000, Xanthomonas axonopodis pv. citri, but can’t repress the HR induced by lmg/ml chitosan. Then we determined the condition of oxidative burst of tobacco leaf tissues. The results were in accordance with the results of plant assays. The results of semi-quantitative PCR showed that IAA had different effects on the expressions of hypersensitive response marker gene hsr203J, disease defense gene chia5and PR-1b, auxin related genes A UX1、ARF8and so on.According to the results of plant assays, oxidative burst of tobacco leaf tissues and semi-quantitative PCR, the conclusion is that auxin can reverse the hypersensitive response stimulated by harpinxoo protein on tobacco leaves without coated with IAA directly, and IAA can repress the HR stimulated by Pseudomona syringae pv. tomato DC3000, Xanthomonas axonopodis pv. citri, while can’t repress the HR induced by chitosan.