Abscisic Acid And Ethylene Signaling Interaction In Plant Growth Enhanced By HrpN_Ea

Harpins are glycine-rich,protease-sensitive,heat-stable,acidic proteins produced by Gram-negative plant pathogenic bacterial,and are required for induction of the hypersensitive response(HR) or hypersensitive cell death(HCD) in nonhost plants of bacteria.Application of harpins to many plants can enhance plant growth,induce resistance to pathogens,insects and drought.These effects have been observed in plants treated with HrpNEa from Eriwinia amylovora,HrpZ_Pss from Pseudomonas syringae pv.syringae, HrpZ_psph from P syringae pv.Phaseolicola,and HpaG_Xoo from Xanthomonas oryzae pv. oryzae.How harpins perform these diverse functions has not been well demonstrated.1.Root growth ofArabidopsis thaliana is regulated by ABA and ethylene signaling interaction in response to HrpN_EaTreating plants with HrpN_Ea stimulates ethylene and abscisic acid(ABA) to induce plant growth and drought tolerance,respectively.Herein,we report that both growth hormones cooperate to mediate the role of HrpNEa in promoting root growth of Arabidopsis thaliana seedlings.Root growth is promoted coordinately with elevation in levels of ABA and ethylene subsequent to soaking of germinating seeds of wild-type(WT) Arabidopsis in a solution of HrpN_Ea.However,these responses are arrested by inhibiting WT roots from synthesizing ethylene as well as sensing of ABA and ethylene.The effects of HrpN_Ea on roots are also nullified in ethylene-insensitive etr1-1 and ein5-1 mutants and in the ABA-insensitive mutant abi2-1 of Arabidopsis.These results provide evidence for presence of a relationship between root growth enhancement and signaling by ABA and ethylene in response to HrpN_Ea.Nevertheless,when HrpN_Ea is applied to leaves,ethylene signaling is active in the absence of ABA signaling to promote plant growth.This suggests the presence of a different signaling mechanism in leaves from that in roots.2.The construction and generation of a double mutant involving ABA and ethylene signal pathways.Ethylene is one of the most important endogenous signals in plant growth and development.It induces the primary disease-resistant response signaling pathway,which is essential for the fundamental self-defense by plants.Abscisic acid(ABA) as the stress hormone modulated many important events in plant growth and development which include modulating stoma closing,resistance to stresses,promoting seeds maturity and dormancy. The roles of ABA and ethylene in plant growth are mostly antagonistic.Specifically,ABA at high concentrations inhibits the synthesis of ethylene.We constructed ABI2-silencing vector,which was able to silence ABI2 in ein2-1 for further study on the roles of the interaction of ABA and Ethylene in plant development and signal transduction in resistance to disease.The silencing line we obtained was named ein2 abi2 Then distinctions of ein2-1 and ein2 abi2 were detected to study the function of ABI2 in Arabidopsis.This study will provide further materials and evidences for the research of relationship between ABA and Ethylene pathways in plant signal transduction in biostress.3.Transgenic expression of HpaG_Xoo of enhances plant growth and confers resistance.Harpins,a group of proteins produced by plant pathogenic bacteria,elicit hypersensitive cell death(HCD) in non-host plants of bacteria and induce resistance to pathogens and insects and enhance plant growth in many plants.HpaG_Xoo,encoded by the hpaG_Xoo gene of X.oryzae pv.oryzae,is a member of harpin group of proteins.Like others harpins,HpaG_Xoo induces HR and others various effects in the plant.Here we show that expression of the hpaG_Xoo gene in transgenic Arabidopsis enhances plant growth and confers pathogen defense without HCD.Resistance to Pseudomonas syringae pv.tomato DC3000 was enhanced at various levels in HATA1 lines.Genes NPR1,PR-1,PR3b,which are involved in pathogen defense,were expressed to various levels in HATA1 plants tested. However,cell death was not observed in HATA1 plants.Based on these data,we concluded that expression of HpaG_Xoo in transgenic Arabidopsis plants enhances plant growth and induces expression of defense-related genes and confers nonspecific resistance to pathogenic bacteria in the absence of HCD.In addition,plant growth and resistance to bacteria expression can be induced in transgenic plants expressing HpaG_Xoo constructed with or without a signal peptide in the transformation unit.