title: The intracellular citrus huanglongbing bacterium, 'Candidatus Liberibacter asiaticus' encodes two novel autotransporters.
abstract: Proteins secreted by the type V secretion system (T5SS), known as autotransporters, are large extracellular virulence proteins localized to the bacterial poles. In this study, we characterized two novel autotransporter proteins of 'Candidatus Liberibacter asiaticus' (Las), and redesignated them as LasAI and LasAII in lieu of the previous names HyvI and HyvII. As a phloem-limited, intracellular bacterial pathogen, Las has a significantly reduced genome and causes huanglongbing (HLB), a devastating disease of citrus worldwide. Bioinformatic analyses revealed that LasAI and LasAII share the structural features of an autotransporter family containing large repeats of a passenger domain and a unique C-terminal translocator domain. When fused to the GFP gene and expressed in E. coli, the LasAI C-terminus and the full length LasAII were localized to the bacterial poles, similar to other members of autotransporter family. Despite the absence of a typical signal peptide, LasAI was found to localize at the cell surface by immuno-dot blot using a monoclonal antibody against the partial LasAI protein. Its surface localization was also confirmed by the removal of the LasAI antigen using a proteinase K treatment of the intact bacterial cells. When co-inoculated with a P19 gene silencing suppressor and transiently expressed in tobacco leaves, the GFP-LasAI translocator targeted to the mitochondria. This is the first report that Las encodes novel autotransporters that target to mitochondria when expressed in the plants. These findings may lead to a better understanding of the pathogenesis of this intracellular bacterium.
authors.affiliation: United States Horticultural Research Laboratory, United States Department of Agriculture-Agriculture Research Service, Fort Pierce, Florida, United States of America.
authors.forename: Guixia
authors.initials: G
authors.lastname: Hao
authors.forename: Michael
authors.initials: M
authors.lastname: Boyle
authors.forename: Lijuan
authors.initials: L
authors.lastname: Zhou
authors.forename: Yongping
authors.initials: Y
authors.lastname: Duan
mesh_terms: D020561:Alphaproteobacteria / Q000235:genetics* / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002957:Citrus / Q000382:microbiology*; D019295:Computational Biology / Q000379:methods; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism / Q000382:microbiology; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology; D017434:Protein Structure, Tertiary; D014026:Nicotiana / Q000382:microbiology; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D037521:Virulence Factors; D049452:Green Fluorescent Proteins