title: The Xanthomonas citri effector protein PthA interacts with citrus proteins involved in nuclear transport, protein folding and ubiquitination associated with DNA repair.
abstract: Xanthomonas axonopodis pv. citri utilizes the type III effector protein PthA to modulate host transcription to promote citrus canker. PthA proteins belong to the AvrBs3/PthA family and carry a domain comprising tandem repeats of 34 amino acids that mediates protein-protein and protein-DNA interactions. We show here that variants of PthAs from a single bacterial strain localize to the nucleus of plant cells and form homo- and heterodimers through the association of their repeat regions. We hypothesize that the PthA variants might also interact with distinct host targets. Here, in addition to the interaction with alpha-importin, known to mediate the nuclear import of AvrBs3, we describe new interactions of PthAs with citrus proteins involved in protein folding and K63-linked ubiquitination. PthAs 2 and 3 preferentially interact with a citrus cyclophilin (Cyp) and with TDX, a tetratricopeptide domain-containing thioredoxin. In addition, PthAs 2 and 3, but not 1 and 4, interact with the ubiquitin-conjugating enzyme complex formed by Ubc13 and ubiquitin-conjugating enzyme variant (Uev), required for K63-linked ubiquitination and DNA repair. We show that Cyp, TDX and Uev interact with each other, and that Cyp and Uev localize to the nucleus of plant cells. Furthermore, the citrus Ubc13 and Uev proteins complement the DNA repair phenotype of the yeast Deltaubc13 and Deltamms2/uev1a mutants, strongly indicating that they are also involved in K63-linked ubiquitination and DNA repair. Notably, PthA 2 affects the growth of yeast cells in the presence of a DNA damage agent, suggesting that it inhibits K63-linked ubiquitination required for DNA repair.
authors.affiliation: Centro Nacional de Pesquisa em Energia e Materiais, Campinas, SP, Brazil.
authors.forename: Mariane Noronha
authors.initials: MN
authors.lastname: Domingues
authors.forename: Tiago Antonio
authors.initials: TA
authors.lastname: De Souza
authors.forename: Raúl Andrés
authors.initials: RA
authors.lastname: Cernadas
authors.forename: Maria Luiza Peixoto
authors.initials: ML
authors.lastname: de Oliveira
authors.forename: Cássia
authors.initials: C
authors.lastname: Docena
authors.forename: Chuck Shaker
authors.initials: CS
authors.lastname: Farah
authors.forename: Celso Eduardo
authors.initials: CE
authors.lastname: Benedetti
mesh_terms: D021581:Active Transport, Cell Nucleus; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002957:Citrus / Q000166:cytology / Q000378:metabolism*; D004260:DNA Repair; D000090263:Leucine-Rich Repeat Proteins; D008239:Lysine / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology / Q000378:metabolism; D000071336:Transcription Activator-Like Effectors; D054875:Ubiquitination
chemical_list: D001426:Bacterial Proteins; D000090263:Leucine-Rich Repeat Proteins; D010940:Plant Proteins; D011506:Proteins; C077723:PthA protein, Xanthomonas campestris; D000071336:Transcription Activator-Like Effectors; D008239:Lysine