Ralstonia solanacearum type III effector RipAA targets chloroplastic AtpB to modulate an incompatible interaction on Nicotiana benthamiana

IntroductionThe type III effector RipAA of Ralstonia solanacearum GMI1000 plays a critical role in the incompatible interaction on Nicotiana benthamiana. MethodsThe RipAA was transiently expressed in N. benthamiana by Agrobacterium-mediated transformation. Chemical staining with trypan blue and DAB were conducted to examine the cell death and the accumulation of hydrogen peroxide (H2O2), respectively. The expression of the marker genes for salicylic acid (SA) and jasmonic acid (JA) signaling was evaluated by quantitative reverse transcription PCR (qRT-PCR). The proteins interacted with RipAA was identified from N. benthamiana by yeast two-hybrid and pull-down assays. A TRV-mediated gene silencing was used to assess the role of host gene in response to RipAA expression and R. solanacearum infection. Results and discussionRipAA induced the accumulation of hydrogen peroxide (H2O2) and genome DNA degradation in N. benthamiana, which were accompanied by a hypersensitive reaction. Simultaneously, the marker genes for salicylic acid (SA) signaling were induced and those for jasmonic acid (JA) signaling were reduced. N. benthamiana chloroplastic AtpB, the ATPase beta subunit, was identified as an interactor with RipAA. The silencing of atpB in N. benthamiana resulted in the inability of RipAA to induce a hypersensitive response, a compatible interaction with GMI1000, and an enhanced sensitivity to bacterial wilt. Our data support the concept that RipAA determines host-range specificity by targeting the host chloroplastic AtpB.

Automated summary

Researchers have found that the type III effector protein RipAA of Ralstonia solanacearum GMI1000 plays a critical role in Nicotiana benthamiana. RipAA expression in the plant leads to the accumulation of hydrogen peroxide (H2O2) and degradation of genomic DNA, accompanied by a hypersensitive reaction. It also alters the expression of marker genes in the salicylic acid (SA) and jasmonic acid (JA) signaling pathways. RipAA interacts with the chloroplastic AtpB protein in N. benthamiana, and silencing of the atpB gene reduces the ability of RipAA to induce a hypersensitive response and a compatible interaction with GMI1000, while increasing sensitivity to bacterial wilt.