The Analysis To Function Of Rubber Tree Powdery Mildew Effector EqIsc1 In Infection

Many plant pathogens must secrete a series of effectors into plant cells to inhibit the host plant’s defense response,promoting its colonization.In fungi and oomycetes,it is found that secretory isochorismatases can be used as effector to inhibit the synthesis of salicylic acid in plants and destroy the immune system of host plants.Powdery mildew is one of the most serious diseases in rubber tree and its pathogen is Erysiphe quercicola(once classified as Oidium heveae),which causes severe damage to natural rubber production.The study of the effectors of E.quercicola will better reveal the pathogenic mechanism at the molecular level,and provide theoretic information for the effective prevention and control of rubber tree powdery mildew.However,such study is relatively lacking.In this study,EqIsc1,the only one isochorismatase-encoding gene in E.quercicola was identified by bioinformatics.And how EqIsc1 functions as effector was preliminary investigated.The main results of this study are as follows:1.Bioinformatic analysis showed that EqIsc1 has an isochorismatase domain and belongs to the isochorismatase protein family;EqIsc1 has 52.9% and 43.3%amino acid sequence similarities with the isochorismatase enzymes Vd Isc1 and Ps Isc1 of Verticillium dahliae and Phytophthora sojae,respectively.It has the closest relationship with Erysiphe necator of powdery mildew,and the homology between the two proteins is 80%.Like Vd Isc1 and Ps Isc1,EqIsc1 does not contain signal peptide and is predicted as non-classical secreted protein.2.By applying the Saccharomyces cerevisiae YTK12,Magnaporthe grisea,and Saccharomyces cerevisiae secretion systems,EqIsc1 was verified as a secreted protein.3.The qRT-PCR results showed that the expression level of EqIsc1 gene increased during the infection of E.quercicola,and the gene expression reached a peak at 12 hpi,suggesitng that EqIsc1 plays a important role in the early stage of infection.4.Expression of EqIsc1 in Nicotiana benthamiana can promote the infection of Phytophthora capsici.And the expression of EqIsc1 in Colletotrichum gloeosporioides can promote the infection of the pathogen on rubber leaves.EqIsc1 can significantly inhibit the accumulation of callus induced by chitin in N.benthamiana.Those results preliminary suggest that EqIsc1 promote infection by disturb plant defense response.5.We found that EqIsc1 interacts with Hb MAPKKK5 of the host plant’s MAPK kinase pathway by Pull-down and CO-IP technologies.Expression of Hb MAPKKK5 in N.benthamiana can inhibit the infection of P.capsici but can promote the accumulation of callus,indicating that Hb MAPKKK5 can positively regulate the defense response of plants to pathogen,while the expression of EqIsc1 accelerates the degradation of Hb MAPKKK5 protein.In summary,EqIsc1 disrupts the immune system of the plant by interfering with the function of HbMAPKKK5.