The type III secretion system translocates effector proteins into plant cells to support bacterial virulence, proliferation, and dissemination. The largest effector family of Xoo is the transcription activator-like (TAL) effector family (also called the avrBs3/pthA family) (Boch and Bonas 2010). A common feature shared by TAL effectors is the central repeat region that consists of 1.5 to 28.5 repeats, with each repeat containing 33–34 amino acids, and contributes to binding the cis-elements named UTP (upregulated by TAL effector) boxes of plant gene promoters, the amino-terminal translocation region, the carboxyl-terminal nuclear localization signal, and carboxyl-terminal acidic transcription activator-like domain (Boch et al. 2009; Kay and Bonas 2009; Yuan and Wang 2012).