The Phloem-based Defense Against Aphids And The Regulatory Role Of Ethylene Signaling In Wheat

The infestation of aphids is accomplished by favorable feeding behavior of probing in sieve elements through plant cortex with the specialized stylet and the rapid colonization dependent on the powerful fertility.The aphid infestation always leads to phytohormone disorders and phenotypic alternations adapted to pest infestation.Almost all the signaling pathways in response to biotic stress are involved in the complicating process of regulating plant defense activities against aphids.According to previous studies on defense responses in Arabidopsis against Myzus persicae,the application of Hpal protein,the broad-spectrum elicitor secreted by rice bacterial pathogen Xanthomonas oryzae pv.oryzicola,induced resistance in the host plants to aphids.Phloem-based defense was activated for inhibiting the feeding behavior and the fecundity due to enhancement of ethylene signaling induced by Hpa1.The short peptide consisting of amino acid 10 to 42 in Hpal functions more effectively than the full-length protein.AtMYB44 is one of the most responsive transcriptional factors in biotic stress treatment.Based on these realistic foundations,Hpal10-42 and fragment of biotic inducible-promoter 44P2000 were combined in the transformation vector.Transgene technology was utilized to modified wheat breeding for expressing Hpa110-42 in wheat taking normal breeds as parent material.The research aims to verify the pest controlling efficiency of transgenic wheat and to clarify the mechanism of induced resistance to aphids.1.The Transgenic Host Wheat Lines Expressing Hpa110-42 Affect The Aphid Feeding Behavior And Physiology PerformanceTransgenic wheat lines expressing Hpa110-42 exhibited high level of efficiency in the pest controlling of English grain aphids as the same with imidacloprid.The aphids feeding preference and colonization were weaken on the transgenic wheat lines in contrast with the normal breed.Artificial infestation experiments of aphids were taken to measure the altered behavior and performance of aphid influenced by the genotypic variation.Aphids feeding on transgenic wheat lines presented with phenotypic characters as longer development duration and weight induction.Also the feeding behavior in phloem was verified to be inhibited on the transgenic wheat lines.These phenomena suggest that aphids-resistance were elicited in the transgenic wheat lines,and the direct function occurred in the phloem.2.Ethylene-Dependent Regulatory Mechanism In Wheat Phloem-Based Defense Against Wheat AphidsThe verification analysis of Hpa110-42 expressing level was taken among different genotypic wheat breeds.Only transgenic wheat lines under aphids attack were tested out for Hpa110-42 expression at different levels suggesting an inducible expression of this fragment.Artificial infestation experiments were taken before the test of phloem-based defense.Microscopic inspections observe the callose deposition in sieve elements,causing the block of sieve tubes and the PBD related genes showed up to be upregulated in transgenic wheat.The expressing analysis of responsive gene suggested that the expression of EIN2,the key regulatory factor of ethylene signaling,increased after aphids infestation.Inhibitory treatment of plant ethylene signaling resulted in decreasing of PBD response and the callose deposition was neutralized by the interruption of ethylene transduction.The experiments verify that pest-induced ethylene signaling is an essential pathway for Hpa1-induced wheat defense responses,and EIN2 is a necessary factor in ethylene-dependent regulation.