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Understanding the roles of TAL effectors in Xanthomonas oryzae interactions with rice

Date

2013

Authors

Corral, Rene, author
Leach, Jan E., advisor
Verdier, Valérie, advisor
Hess, Ann, committee member

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Abstract

Transcription activator like (TAL) effector proteins are virulence factors that are secreted by Xanthomonas oryzae. Some TAL effectors contribute to virulence by activating transcription of plant host susceptibility genes thereby modulating the plant's physiology and creating a more pathogen favorable environment. Some TAL effectors activate transcription of disease resistance genes. Because most X. oryzae strains encode many (between 8 and 26) genes for TAL effectors, it is difficult to evaluate the function of individual TAL in the plant-pathogen interaction. In this study, we introduced the use of a TAL deficient strain of X. oryzae that allows study of individual TAL effectors. We demonstrated that the TAL deficient strain could deliver TAL to rice, and that subtle differences in TAL virulence functions could be measured in interactions with rice when delivered by this strain. Plants have evolved resistance genes that detect or recognize TAL effectors and activate resistance responses. Using the TAL deficient X. oryzae delivery system, we isolated a TAL that activates resistance in plants which are homozygous for the recessive resistance gene xa5. The TAL, Avrxa5P86, is predicted to target many transcription factors. Avrxa5P86 not only interacted with xa5 to confer resistance, but also exhibited a novel resistance interaction with Azucena and Nipponbare, both homozygous for the Xa5 allele. Our discovery of Avrxa5P86 is of presents a novel interaction that raises new evolutionary questions about TAL effectors and/or resistance genes in rice.

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