Xanthomonas AvrBsT interacts with calmodulin (CaM) and its CaM-binding domain is required for activation of effector-triggered immunity.
M. CHENONG (1), J. Kim (2), N. Ozabaki-Yagan (2), Y. Wang (3), M. Mudgett (2) (1) Department of Biology, Stanford University, U.S.A.; (2) Stanford University, U.S.A.; (3) China Agricultural University, China

The YopJ effector family is one of the largest and most widely distributed group of bacterial virulence factors translocated by the type III secretion (T3S) system into host cells during infection. Several of these effectors have acetyltransferase activity with distinct host substrate specificity. We have shown that the Xanthomonas euvesicatoria YopJ-like protein AvrBsT acetylates ACIP1 (for ACETYLATED INTERACTING PROTEIN1), a microtubule-associated protein that is required for PAMP- and effector-triggered immunity (ETI) in Arabidopsis. The molecular mechanism by which AvrBsT is recognized and activates ETI signaling is unknown. We discovered that AvrBsT contains a putative calmodulin (CaM) binding domain (CaM-BD) at its C-terminus. Thus, we hypothesized that AvrBsT-triggered immunity might involve calcium signaling and/or direct binding to CaM. Here we provide evidence that links Ca2+/CaM signaling to AvrBsT-dependent disease resistance. First, treatment of resistant Arabidopsis Pi-0 leaves treated with LaCl3 (a calcium channel blocker) or W7 (a CaM antagonist) suppresses the AvrBsT-triggered hypersensitive response. Second, CaM affinity purified GST-AvrBsT in vitro in a Ca2+-dependent manner. Binding required basic and nonpolar amino acids in the CaM-BD of AvrBsT. Third, AvrBsT’s CaM-BD is required for AvrBsT-triggered immunity in three plant genera, including Arabidopsis, Capsicum and Nicotiana. Taken together, our data suggests that formation of an AvrBsT/CaM complex is required for molecular recognition of AvrBsT in planta.

Abstract Number: P17-547
Session Type: Poster