Pathogenic Gram-negative bacteria interact with their eukaryotic hosts by deploying the type III translocon to inject effector proteins into the cytosol of eukaryotic cells. The translocon compositions， the number and biochemical characteristics of type III translocators in animal-pathogenic bacteria have been well elucidated， but information is lacking for plant-pathogenic bacteria. With extensive studies on biological functions of the Hpa1 protein secreted by the type III secretion system in Xanthomonas oryzae pv. oryzae (Xoo)， we show here that Hpa1 is a type III translocator based on measurements of two proteins categorized as transcription activator-like (TAL) effector.