TAL effectors target the C-terminal domain of RNA polymerase II (CTD) by inhibiting the prolyl-isomerase activity of a CTD-associated cyclophilin.
Transcriptional activator-like (TAL) effectors of plant pathogenic bacteria function as transcription factors in plant cells. However, how TAL effectors control transcription in the host is presently unknown. Previously, we showed that TAL effectors of the citrus canker pathogen Xanthomonas citri, named PthAs, targeted the citrus protein complex comprising the thioredoxin CsTdx, ubiquitin-conjugating enzymes CsUev/Ubc13 and cyclophilin CsCyp. Here we show that CsCyp complements the function of Cpr1 and Ess1, two yeast cyclophilins that regulate transcription by the isomerization of proline residues of the regulatory C-terminal domain (CTD) of RNA polymerase II. We also demonstrate that CsCyp, CsTdx, CsUev and four PthA variants interact with the citrus CTD and that CsCyp co-immunoprecipitate with the CTD in citrus cell extracts and with PthA2 transiently expressed in sweet orange epicotyls. The interactions of CsCyp with the CTD and PthA2 were inhibited by cyclosporin A (CsA), a cyclophilin inhibitor. Moreover, we present evidence that PthA2 inhibits the peptidyl-prolyl cis-trans isomerase (PPIase) activity of CsCyp in a similar fashion as CsA, and that silencing of CsCyp, as well as treatments with CsA, enhance canker lesions in X. citri-infected leaves. Given that CsCyp appears to function as a negative regulator of cell growth and that Ess1 negatively regulates transcription elongation in yeast, we propose that PthAs activate host transcription by inhibiting the PPIase activity of CsCyp on the CTD.
Laboratório Nacional de Biociências, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, Brazil.
Mariane Noronha
MN
Domingues
Bruna Medeia de
BM
Campos
Bruna Medeia
BM
de Campos
Maria Luiza Peixoto
ML
de Oliveira
Uli Quirino
UQ
de Mello
Celso Eduardo
CE
Benedetti
D001426:Bacterial Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002957:Citrus / Q000201:enzymology / Q000382:microbiology; D021983:Cyclophilins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D020868:Gene Silencing; D005816:Genetic Complementation Test; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012319:RNA Polymerase II / Q000737:chemistry* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013879:Thioredoxins / Q000378:metabolism; D014974:Xanthomonas / Q000502:physiology
D001426:Bacterial Proteins; D029701:Saccharomyces cerevisiae Proteins; D013879:Thioredoxins; D012319:RNA Polymerase II; D021983:Cyclophilins