Study On The Bioglogical Function And Molecular Mechanisms Of Ralstonia Solanacearum RipNE2

Bacterial wilt is a typical soil-borne disease caused by Ralstonia solanacearum,with its wide host range and high adaptability.Bacterial wilt becomes a serious threat to the safety of agricultural production and causes huge economic losses worldwide,therefore,it is important to study and understand the molecular mechanism of the pathogenesis of R.solanacearum.Effectors secreted by the type III secretion system of R.solanacearum play an important role in attacking the immune response of plants.Although studies on the biological functions of type III effectors have been reported constantly in recent years,few of them are focused on effectors that exert their functions in the nucleus.Given this,our research aims to screen effectors that can enter plant nucleus to regulate host immune gene expression and analyze their molecular mechanisms,aiming to reveal the new mechanism of pathogen bacteria and host interaction in plant nucleus,as well as to provide new methods and materials for plant molecular breeding against bacterial wilt.Results of this study are as follows:Eight effectors with unknown functions were screened out from the 73 type III effectors of GMI1000 strain and were named as Rip NEs.The influence of these effectors on immune gene expression was tested.It was found that Rip NE2,which has a typical nuclear localization signal,significantly inhibited the induced expression of the immune genes FRK1 and WRKY30 as well as other immune responses such as ROS,it was also found that the biological function of Rip NE2 is dependent on its nuclear localization signal.Then,transgenic lines of Arabidopsis thaliana that over-expressing Rip NE2 were generated,which exhibited compromised expression of immune genes and were more sensitive to R.solanacearum.These results indicate that Rip NE2 plays an important role in bacterial infection of plants.Furthermore,the target proteins of Rip NE2 in plants were screened and identified.It was found that At TGA2,an important factor of salicylic acid signaling pathway,showed strong interaction with Rip NE2.Subsequently,the members of the TGA family involved in plant defense were cloned and their interaction with Rip NE2 was tested,it was found that Rip NE2 interacted with TGA2,TGA5 and TGA6,which belong to group II.Meanwhile,transgenic plants expressing Rip NE2 showed some interesting phenotypes such as sensitive to high levels of SA,reduced induction of resistance,and compromised induction of SA marker gene expression,which are similar to that of tga2/5/6 mutant plants.Preliminary results suggest that Rip NE2 hijacks the proteins of TGAs,interfering with their biological function and thus affecting the SA signaling resistance pathway,while how Rip NE2 negatively regulates the molecular functions of TGA transcription complexes remains to be further investigated.