HrpH, a multipurpose lytic transglycosylase associated with the type III secretion system of Pseudomonas syringae pv. tomato DC3000 
H. WEI (1), A. Collmer (1) (1) School of Integrative Plant Science, Section of Plant Pathology and Plant-Microbe Biology, Cornell University, U.S.A.

The bacterial pathogen Pseudomonas syringae pv. tomato DC3000 injects 36 effectors into host cells via the type III secretion system (T3SS), which collectively suppress the two-tiered innate immune system of plants. The hrpH lytic transglycosylase gene is located between hrpR and avrE in the Hrp pathogenicity island and is carried in the functional cluster of P. syringae pv. syringae 61 hrp genes cloned in cosmid pHIR11. HrpH was previously reported to be involved in effector translocation into plant cells but not effector secretion in culture and to be translocated into plant cells itself. Here we show that the specialized lytic transglycosylase (SLT) domain of HrpH (amino acids 116-241) and its conserved glutamate 148 are necessary for HopA1 translocation and HopA1-dependent cell death elicitation in tobacco. P. fluorescence Pf0-1 expressing pCPP6227, a HopA1 and AvrE-deficient mutant of pHIR11, does not trigger cell death in tobacco, but it surprisingly elicits cell death in tomato cultivar Moneymaker. Deletion of hrpH from pCPP6227 eliminated cell death elicitation in tomato. The SLT domain of HrpH was sufficient to restore this cell death activity, but the ability was not dependent on the conserved glutamate. The results suggest that tomato Moneymaker recognizes the SLT domain of the HrpH protein independent of its activity. 

Abstract Number: P9-320
Session Type: Poster