Two type III effector genes of Xanthomonas oryzae pv. oryzae control the induction of the host genes OsTFIIAγ1 and OsTFX1 during bacterial blight of rice

Xanthomonas oryzae pv. oryzae strain pX099(A) induces the expression of the host gene Os8N3, which results in increased host susceptibility to bacterial blight of rice. Here, we show that pX099(A) affects the expression of two additional genes in a type III secretion system-dependent manner, one encoding a bZIP transcription factor (OsTFX1) and the other the small subunit of the transcription factor IIA located on chromosome 1 (OsTFIIA gamma 1). Induction of OsTFX1 and OsTFIIA gamma 1 depended on the type III effector genes pthXo6 and pthXo7, respectively, both encoding two previously undescribed members of the transcription activator-like (TAL) effector family. pthXo7 is strain-specific and may reflect adaptation to the resistance mediated by xa5, an allele of OsTFIIA gamma 5 encoding a second form of the TFIIA small subunit on chromosome 5 of rice. The loss of pthXo6 resulted in reduced pathogen virulence, and ectopic expression of OsTFX1 abrogated the requirement for pthXo6 for full virulence. X. oryzae pv. oryzae therefore modulates the expression of multiple host genes using multiple TAL effectors from a single strain, and evidence supports the hypothesis that expression of the associated host genes contributes to host susceptibility to disease.