Promoter elements of rice susceptibility genes are bound and activated by specific TAL effectors from the bacterial blight pathogen, Xanthomonas oryzae pv. oryzae

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Abstract
• Plant pathogenic bacteria of the genus Xanthomonas inject transcription activator‐like effector (TALe) proteins that bind to and activate host promoters, thereby promoting disease or inducing plant defense. TALes bind to corresponding UPT (up‐regulated by TALe) promoter boxes via tandemly arranged 34/35‐amino acid repeats. Recent studies uncovered the TALe code in which two amino acid residues of each repeat define specific pairing to UPT boxes. • Here we employed the TALe code to predict potential UPT boxes in TALe‐induced host promoters and analyzed these via β‐glucuronidase (GUS) reporter and electrophoretic mobility shift assays (EMSA). • We demonstrate that the Xa13, OsTFX1 and Os11N3 promoters from rice are induced directly by the Xanthomonas oryzae pv. oryzae TALes PthXo1, PthXo6 and AvrXa7, respectively. We identified and functionally validated a UPT box in the corresponding rice target promoter for each TALe and show that box mutations suppress TALe‐mediated promoter activation. Finally, EMSA demonstrate that code‐predicted UPT boxes interact specifically with corresponding TALes. • Our findings show that variations in the UPT boxes of different rice accessions correlate with susceptibility or resistance of these accessions to the bacterial blight pathogen.

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