Diverse plant genes are targeted by TAL effectors for disease susceptibility
J. ZHANG (1), H. Yang (2), H. Jia (3), D. Sosso (4), W. Frommer (5), Y. Bing (6), N. Wang (3), J. Jones (2), F. White (1). (1) Kansas State University, Manhattan, KS, U.S.A.; (2) University of Florida, Gainesville, FL, U.S.A.; (3) University of Florida, Lake Alfred, FL, U.S.A.; (4) Stanford University, Stanford, CA, U.S.A.; (5) Carnegie Institution of Science, Stanford, CA, U
Bacterial citrus canker is incited by distinct yet related strains of <i>Xanthomonas</i>. <i>X. citri</i> subsp. <i>citri</i> strain Xcc306 harbors four type III transcription activator-like (TAL) effector genes, only one of which, <i>pthA4</i>, is required for pustule formation in Xcc306. Transcriptional profiles of citrus leaf tissue infected with the mutant strain Xcc306Δ<i>pthA4</i> compared to profiles from infections by the same strain harboring either <i>pthA4</i> or <i>pthAw</i>, a variant gene from strain XccAw, revealed two up-regulated candidate susceptibility (S) genes that were potentially targeted by <i>pthA4</i> or <i>pthAw</i>. <i>CsLOB1</i> is a member of the LOB transcription factor family, while <i>CsN3-1</i> encodes a member of the SWEET family (MtN3) of sugar transporters. CsN3-1 was shown to transport glucose preferentially in contrast to the transport of sucrose by the major S gene products in rice during bacterial blight disease. Artificial designer TAL effectors (dTALes), targeting the <i>CsLOB1</i> promoter region but not the <i>CsN3-1</i> promoter, restored pustule formation to Xcc306Δ<i>pthA4</i>. Two additional TAL effectors, PthB and PthC, also target <i>CsLOB1</i> expression, yet have no effect on <i>CsN3-1</i> expression. The results indicate that distinct TAL effectors target a single S gene for pustule formation in citrus. Other disease complexes involving <i>Xanthomonas</i> also involve TAL effector genes, and a comparison of the S genes from different diseases will be presented.
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