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Recognition of AvrBs3-Like Proteins Is Mediated by Specific Binding to Promoters of Matching Pepper Bs3 Alleles^1,[W]

Institute of Biology, Department of Genetics (P.R., T.S., S.H., H.S., R.M., U.B., T.L.), and Institute of Informatics (J.G.), Martin Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany

The pepper (Capsicum annuum) bacterial spot (Bs) resistance gene Bs3 and its allelic variant Bs3-E mediate recognition of the Xanthomonas campestris pv vesicatoria type III effector protein AvrBs3 and its deletion derivative AvrBs3rep16. Recognition specificity resides in the Bs3 and Bs3-E promoters and is determined by a defined promoter region, the UPA (for up-regulated by AvrBs3) box. Using site-directed mutagenesis, we defined the exact boundaries of the UPA_AvrBs3 box of the Bs3 promoter and the UPA_AvrBs3rep16 box of the Bs3-E promoter and show that both boxes overlap by at least 11 nucleotides. Despite partial sequence identity, the UPA_AvrBs3 box and the UPA_AvrBs3rep16 box were bound specifically by the corresponding AvrBs3 and AvrBs3rep16 proteins, respectively, suggesting that selective promoter binding of AvrBs3-like proteins is the basis for promoter activation specificity. We also demonstrate that the UPA_AvrBs3 box retains its functionality at different positions within the pepper Bs3 promoter and confers AvrBs3 inducibility in a novel promoter context. Notably, the transfer of the UPA_AvrBs3 box to different promoter locations is always correlated with a new transcriptional start site. The analysis of naturally occurring Bs3 alleles revealed many pepper accessions that encode a nonfunctional Bs3 variant. These accessions showed no apparent abnormalities, supporting the supposition that Bs3 functions only in disease resistance and not in other developmental or physiological processes.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Thomas Lahaye (lahaye{at}genetik.uni-halle.de).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.139931

^* Corresponding author; e-mail lahaye{at}genetik.uni-halle.de.

Received April 14, 2009; accepted May 11, 2009; published May 15, 2009.