Function Analysis Of Ethylene In The Interaction Between Cotton And Verticillium Dahliae

Verticillium wilt poses a serious threat to fiber production of China,especially the defoliating Verticillium dahliae,which can lead to rapid defoliation of diseased cotton,and causes serious reduction in fiber production and quality.Decreasing the defoliation rate of diseased cotton is an effective way to improve the tolerance of cotton to V.dahliae and reduce the loss of production.Ethylene can promote senescence,maturity and the formation of the abscission layer leading to exfoliation.The function of ethylene signaling pathway in the interaction between cotton and Verticillium dahliae was investigated in this study.The main results are as follows:1.The production of ethylene was greatly increased 7 days,9 days and 11 days after inoculated with defoliating V.dahliae ‘V991' and was achieved to 119.49 ?l/kg,126.82 ?l/kg and 148.83 ?l/kg,respectively,which is 1.60,1.33 and 1.51 times higher than the ethylene production of cotton inoculated with non-defoliating V.dahliae ‘1cd3-2'.In addition,exogenous application of 0.5 ?g/ml,2.5 ?g/ml and 12.5 ?g/ml ethephon could aggravate disease symptom of cotton compared with the water treatment control,and the disease index was increased by 18% to 23% at 16 day after inoculated with V.dahliae ‘V991'.2.The gene family of Gh ACOs,which involves in the synthesis of ethylene were isolated in cotton,and the conserved regions of this gene family were selected as targets for virus-induced gene silencing(VIGS)to knock down the expression of Gh ACOs.The results showed that the ethylene production of Gh ACOs-silenced plants decreased significantly at 7 day after inoculated with V.dahliae ‘V991'.Furthermore,the positive regulatory gene Gh EIN2 s in ethylene signaling pathway were isolated and VIGS vectors of this family were constructed according to the conservative sequence.Our study found that knock down of Gh EIN2 s enhanced cotton resistance to V.dahliae and reduced the rate of defoliation caused by ‘V991'.3.We constructed overexpression vector of At CTR1,a negative regulatory gene in ethylene signaling pathway reported in Arabidopsis,and transformed in upland cotton cv ‘YZ1'.Our study found overexpression of At CTR1 decreased the sensitivity of cotton to ethylene.Additionally,overexpression of At CTR1 improved cotton resistance to Verticillium wilt and reduced the rate of defoliation.4.Based on cytological observation,we found ‘V991' inoculation could induce the formation of absciss layer in cotton petiole.Overexpression At CTR1 could retard the formation of absciss layer in cotton petiole.Gene expression analysis showed that the defoliation caused by ‘V991' inoculation was related to the up regulation of absciss layer formation genes,such as Gh BXL1.Whereas,overexpression At CTR1 could depress the expression of these genes.In summary,the above results showed that Verticillium dahliae could induce the synthesis of ethylene in cotton and activated the expression of genes related to absciss layer formation and eventually lead to defoliation of disease plants.Suppression of ethylene signal transduction in cotton significantly improved the tolerance of cotton to V.dahliae and reduced the rate of defoliation.The above results provide theoretical basis and technical support for controlling the occurrence of Verticillium wilt or reducing the harm of Verticillium wilt by regulating the ethylene synthesis or signaling pathway of cotton.