Pseudomonas syringae Effector AvrPtoB Exploits A Plant Defense-Essential Subset Of Ubiquitin-Conjugating Enzymes To Suppress Host Immunity
L. ZENG (1), B. Zhou (1), R. Mural (2), X. Chen (3), M. Oates (4), R. Connor (5), G. Martin (6), J. Gough (4) (1) University of Nebraska-Lincoln, U.S.A.; (2) University of Nebraska-Lincoln, U.S.A.; (3) Fujian Agriculture and Forestry University, China; (4) University of Bristol, United Kingdom; (5) University of Arkansas at Little Rock, U.S.A.; (6) The Boyce Thompson Institute for Plant Research, U.S.A.

The Pseudomonas syringae pv. tomato (Pst) effector AvrPtoB uses its C-terminal ubiquitin ligase (E3) activity to cause degradation of the host Fen kinase which is required for effector-triggered immunity (ETI). Ubiquitin-conjugating enzyme(s) (E2) are suspected to act with the AvrPtoB E3 in suppressing ETI although to date none have been discovered. We identified and cloned forty tomato genes encoding ubiquitin E2 proteins. Thioester assays indicated the majority of the genes encode active E2 enzymes. Phylogenetic analysis classified the forty tomato E2 enzymes into thirteen groups, of which members of group III were found to act with AvrPtoB and the plant-immunity-associated E3, PUB13, to catalyze ubiquitination. Knocking-down expression of group III E2 genes in Nicotiana benthamiana diminished AvrPtoB-promoted degradation of Fen and suppression of ETI-associated programmed cell death and resulted in decreased pattern-triggered immunity (PTI) thus enhancing the growth of Pst. Functional redundancy was found to exist among group III members for their requirement by AvrPtoB in suppressing plant immunity and for the induction of PTI. Knocking-down of the group III E2 genes also impaired the role of PUB13 in attenuating FLS2-mediated immune signaling. Thus, by exploiting a functionally redundant subgroup of host E2s that are essential for plant defense, AvrPtoB has evolved a strategy for suppressing host immunity that is difficult for the plant to thwart.    

Abstract Number: P11-387
Session Type: Poster