The C Terminus of AvrXa10 Can Be Replaced by the Transcriptional Activation Domain of VP16 from the Herpes Simplex Virus

Poecke

Proc. Natl. Acad. Sci. U.S.A.

et al. 2012

113

107

Transcription activator-like effector (TALE) proteins of the plant pathogenic bacterial genus Xanthomonas bind to and transcriptionally activate host susceptibility genes, promoting disease. Plant immune systems have taken advantage of this mechanism by evolving TALE binding sites upstream of resistance ( R ) genes. For example, the pepper Bs3 and rice Xa27 genes are hypersensitive reaction plant R genes that are transcriptionally activated by corresponding TALEs. Both R genes have a hallmark expression pattern in which their transcripts are detectable only in the presence and not the absence of the corresponding TALE. By transcriptome profiling using next-generation sequencing (RNA-seq), we tested whether we could avoid laborious positional cloning for the isolation of TALE-induced R genes. In a proof-of-principle experiment, RNA-seq was used to identify a candidate for Bs4C , an R gene from pepper that mediates recognition of the Xanthomonas TALE protein AvrBs4. We identified one major Bs4C candidate transcript by RNA-seq that was expressed exclusively in the presence of AvrBs4. Complementation studies confirmed that the candidate corresponds to the Bs4C gene and that an AvrBs4 binding site in the Bs4C promoter directs its transcriptional activation. Comparison of Bs4C with a nonfunctional allele that is unable to recognize AvrBs4 revealed a 2-bp polymorphism within the TALE binding site of the Bs4C promoter. Bs4C encodes a structurally unique R protein and Bs4C -like genes that are present in many solanaceous genomes seem to be as tightly regulated as pepper Bs4C . These findings demonstrate that TALE-specific R genes can be cloned from large-genome crops with a highly efficient RNA-seq approach.

Section: Discussionmentioning

confidence: 86%

mentioning

confidence: 99%

RNA-seq pinpoints a Xanthomonas TAL-effector activated resistance gene in a large-crop genome

Poecke

Proc. Natl. Acad. Sci. U.S.A.

et al. 2012

113

107

“…Notably, the aviruence (avrxa5) gene corresponding to xa5 is a member of the AvrBs3 protein family whose products can be secreted into the host cells from the bacteria to trigger the hypersensitive response (HR; Hopkins et al 1992;Rossier et al 1999). The HR induction by the ArvBs3, AvrXa10, and AvrXa7 proteins is dependent on their nuclear localization signals (Zhu et al , 1999Van den Ackerveken et al 1996;Yang et al 2000), and their AAD that could interact with TFIIA small subunit as suggested by a coimmuno-precipitation assay (Kobayashi et al 1995). In addition, some AvrBs3 family proteins have been shown to bind to double-stranded DNA (Yang et al 2000) and specifically up-regulates genes during infection and in the resistance reaction mediated by Xa27 (Marois et al 2002;Gu et al 2005).…”

Section: Discussionmentioning

confidence: 97%

Testifying the rice bacterial blight resistance gene xa5 by genetic complementation and further analyzing xa5 (Xa5) in comparison with its homolog TFIIAγ1

et al. 2006

The recessive gene xa5 for resistance to bacterial blight resistance of rice is located on chromosome 5, and evidence based on genetic recombination has been shown to encode a small subunit of the basal transcription factor IIA (Iyer and McCouch in MPMI 17(12):1348-1354, 2004). However, xa5 has not been demonstrated by a complementation test. In this study, we introduced the dominant allele Xa5 into a homozygous xa5-line, which was developed from a cross between IRBB5 (an indica variety with xa5) and Nipponbare (a japonica variety with Xa5). Transformation of Xa5 and subsequent segregation analysis confirmed that xa5 is a V39E substitution variant of the gene for TFIIAgamma on chromosome 5 (TFIIAgamma5 or Xa5). The rice has an addition gene for TFIIAgamma exists on chromosome 1 (TFIIAgamma1). Analysis of the expression patterns of Xa5 (TFIIAgamma5)/xa5 and TFIIAgamma1 revealed that both the genes are constitutively expressed in different rice organs. However, no expression of TFIIAgamma1 could be detected in the panicle by reverse transcriptase-polymerase chain reaction. To compare the structural difference between the Xa5/xa5 and TFIIAgamma1 proteins, 3-D structures were predicted using computer-aided modeling techniques. The modeled structures of Xa5 (xa5) and TFIIAgamma1 fit well with the structure of TFIIA small subunit from human, suggesting that they may all act as a small subunit of TFIIA. The E39V substitution in the xa5 protein occurs in the alpha-helix domain, a supposed conservative substitutable site, which should not affect the basal transcription function of TFIIAgamma. The structural analysis indicates that xa5 and Xa5 potentially retain their basic transcription factor function, which, in turn, may mediate the novel pathway for bacterial blight resistance and susceptibility, respectively.

“…malvacearum were expressed in the plant cells (15,56). In a separate study, we have observed a 75% reduction in the number of transformation foci after particle bombardment of resistant rice leaves with a plant-expressed copy of avrXa10 (66). Therefore, the protein products of avrXa10 and avrXa7 along with possible virulence factors are likely to be secreted by a hrpencoded type III secretory apparatus into the cells of the rice plant.…”

Section: Discussionmentioning

confidence: 99%

Identification of Two Novel hrp -Associated Genes in the hrp Gene Cluster of Xanthomonas oryzae pv. oryzae

2000

Self Cite

We have cloned a hrp gene cluster from Xanthomonas oryzae pv. oryzae. Bacteria with mutations in the hrp region have reduced growth in rice leaves and lose the ability to elicit a hypersensitive response (HR) on the appropriate resistant cultivars of rice and the nonhost plant tomato. A 12,165-bp portion of nucleotide sequence from the presumed left end and extending through the hrpB operon was determined. The region was most similar to hrp genes from Xanthomonas campestris pv. vesicatoria and Ralstonia solanacearum. Two new hrp-associated loci, named hpa1 and hpa2, were located beyond the hrpA operon. The hpa1 gene encoded a 13-kDa glycine-rich protein with a composition similar to those of harpins and PopA. The product of hpa2 was similar to lysozyme-like proteins. Perfect PIP boxes were present in the hrpB and hpa1 operons, while a variant PIP box was located upstream of hpa2. A strain with a deletion encompassing hpa1 and hpa2 had reduced pathogenicity and elicited a weak HR on nonhost and resistant host plants. Experiments using single mutations in hpa1 and hpa2 indicated that the loss of hpa1 was the principal cause of the reduced pathogenicity of the deletion strain. A 1,519-bp insertion element was located immediately downstream of hpa2. Hybridization with hpa2 indicated that the gene was present in all of the strains of Xanthomonas examined. Hybridization experiments with hpa1 and IS1114 indicated that these sequences were detectable in all strains of X. oryzae pv. oryzae and some other Xanthomonas species.The hrp ("harp") genes encode type III secretory pathways and are required by many phytopathogenic bacteria to elicit a hypersensitive response (HR) on nonhost or resistant host plants and for pathogenesis on susceptible hosts. The HR is a rapid localized death of the host cells that occurs upon pathogen infection and, together with the expression of a complex array of defense-related genes, is a component of plant resistance. The hrp genes were first identified in Pseudomonas syringae pv. phaseolicola, a bean pathogen (38). Since then, hrp genes from a variety of plant pathogenic bacteria, including Erwinia, Pseudomonas, Ralstonia, and Xanthomonas, have been characterized (for reviews, see references 2, 9, and 11). The specific functions of the hrp pathway in pathogenesis are not known. However, type III secretion pathways of animal and plant pathogens have been demonstrated to mediate the secretion of virulence factors into the extracellular melieu. Some of the proteins ultimately end up in the host cell cytoplasm (reviewed in references 11, 25, and 37). In mediating the interaction of the bacterium and the host plant, the hrp pathway presumably acts to prevent or inhibit a general resistance response or otherwise enhance the colonization of the plant by the bacteria.Given the importance of the type III systems to pathogenicity, it can be expected that analysis of the systems in different species will provide insight into the adaptation of the species to their respective host plants. The hrp gene cl...