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Oral: Effector Biology


Resistance of Carolina Gold Select rice to African strains of Xanthomonas oryzae pv. oryzicola is triggered by inactivated TAL effectors
L. TRIPLETT (1), S. Cohen (2), C. Heffelfinger (3), A. Bogdanove (4), J. Leach (2) (1) The Connecticut Agricultural Experiment Station, U.S.A.; (2) Colorado State University, U.S.A.; (3) Yale University, U.S.A.; (4) Cornell University, U.S.A.; (5) Colorad

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The rice pathogen Xanthomonas oryzae pv. oryzicola causes bacterial leaf streak of rice, a disease for which no single-gene resistance is available. The bacterium produces numerous transcription activator-like (TAL) effectors that activate host susceptibility genes. There are two common rice resistance mechanisms against TAL effectors: DNA polymorphisms that allow escape of TAL effector binding, and placement of TAL effector binding sites to cause specific TAL effectors to activate resistance genes. We found that the heirloom rice variety Carolina Gold Select has a third form of resistance, triggered by diverse TAL effectors. The resistance was triggered in a manner independent of the transcriptional activation domain and of the composition of repeat variable diresidues that specify host DNA target sequences. While the TAL effector central repeat region was critical to resistance, an effector with only 3.5 central repeats was sufficient for resistance activation. The resistance was mapped to a single dominant locus, Xo1, on chromosome 4. The Xo1 interval confers complete resistance to strains in the African clade of X. oryzae pv. oryzicola, representing the first dominant resistance locus against bacterial leaf streak in rice. The TAL effector triggered resistance phenotype has strong similarity to that conferred by the tomato resistance gene Bs4, suggesting that monocots and dicots have converged on the structure of TAL effectors as a pattern triggering resistance.