Involvement Of The Heterotrimeric G Protein In The Defense Responses Of Wheat To Its Leaf Rust Disease

Wheat leaf rust caused by Puccinia triticina is one of the major diseases in wheat. Applying the disease-resistant varieties is a promising way to control wheat leaf rust if the molecular mechanism of wheat resistance are fully understood.Accumulating evidence from Arabidopsis thalina,tomato and rice demonstrated that heterotrimeric G protein play an essential role in regulating plant growth,development,and the response to hormone, light and pathogens.The roles of heterotrimeric G protein in wheat resistance to its leaf rust disease were investigated at phenotype,bio-chemical and molecular level,respectively,using wheat NIL Lrl and P.triticina with different virulence as materials.The results were as follow:(1)The detached leave were pretreated with heterotrimeric G protein activator(GTPγS, Mastoparan-7)or inhibitor PTX,and then were inoculated with virulent leaf rust race 05-22-64 or avirulent race 05-8-63①,respectively,the infection types were observed at the 9th day.It was found that the occurrence of leaf rust disease was delayed 4 days by pretreating the leaves with the activators when compared to the untreated leaves,whereas no difference in the development of wheat leaf rust disease was observed between the leaves pretreated with the inhibitor of heterotrimeric G protein and the untreated ones if both were inoculated with the avirulent race 05-8-63①.(2)The profile of enzyme activities of POD,PAL,PPO were followed in wheat leaf after the detached leave were treated with GTPγS and Mastoparan-7,or inoculated with the avirulent race 05-8-63①alone,or the detached leave were first treated with and then inoculated with the avirulent race 05-8-63①.The results showed that the activities of these defensive enzymes were induced by treating wheat leave with heterotrimeric G protein activators,comparable to that of leave inoculated with the avirulent race;these enzyme activities were inhibited by heterotrimeric G protein inhibitor PTX,which could be induced by inoculation of the avirulent race.(3)The expression of the heterotrimeric G protein a subunit gene was evaluated by semi-quantitative RT-PCR after inoculating the wheat with the virulent race and avirulent race,respectively.The results indicated that the avirulent race enhanced the expression of the heterotrimeric G proteinαsubunit gene,the expression level reached the peak at 48 h. However,the virulent race inhibited its expression,the expression began to decrease at 6 h and reached the lowest level at 12 h.Taken together,these data demonstrated that heterotrimeric G protein might be involved in the signaling of wheat defense response to its leaf rust disease.