Transient Expression Assay in N. benthamiana 
The avrRps4 and popP2 DNA fragments were amplified from Pst-avrRps4 and Ralstonia solanacearum strain RS1002 genomic DNA, respectively, by PCR using avrRps4 and popP2 primers listed in Table S1, and cloned into pCR8GW-TOPO. The pSfinx vector [35] was converted into a Gateway destination vector using the Gateway Vector Conversion System (Life Technologies). A Gateway Reading Frame Cassette B was introduced into the original cloning cassette of the pSfinx vector using the SmaI site. The avrRps4 and popP2 DNA fragments were cloned into the modified pSfinx vector using the LR cloning reaction (pSfinx-avrRps4 and pSfinx-popP2, respectively). N. benthamiana plants were grown in a growth chamber at 25°C with 16-h light. Plants at the age of four-week-old were used in the experiment. Overnight bacterial cultures of A. tumefaciens strain GV3101 (pMP90, pSoup) containing pSfinx-avrRps4 or pSfinx-popP2 were harvested by centrifugation. Cells were washed three times in induction buffer (10 mM MES, pH 5.6, 10 mM MgCl2 and 150 µM acetosyringone), re-suspended in induction buffer to an OD600 of 0.5, and incubated for 2 h at room temperature. Agrobacterium cells were hand-infiltrated into N. benthamiana leaves with a 1 ml syringe. Cell death responses began to appear on infiltrated leaves 5 d after infiltration.