title: Rhamnose synthase activity is required for pathogenicity of the vascular wilt fungus Verticillium dahliae.
abstract: The initial interaction of a pathogenic fungus with its host is complex and involves numerous metabolic pathways and regulatory proteins. Considerable attention has been devoted to proteins that play a crucial role in these interactions, with an emphasis on so-called effector molecules that are secreted by the invading microbe to establish the symbiosis. However, the contribution of other types of molecules, such as glycans, is less well appreciated. Here, we present a random genetic screen that enabled us to identify 58 novel candidate genes that are involved in the pathogenic potential of the fungal pathogen Verticillium dahliae, which causes vascular wilt diseases in over 200 dicotyledonous plant species, including economically important crops. One of the candidate genes that was identified concerns a putative biosynthetic gene involved in nucleotide sugar precursor formation, as it encodes a putative nucleotide-rhamnose synthase/epimerase-reductase (NRS/ER). This enzyme has homology to bacterial enzymes involved in the biosynthesis of the nucleotide sugar deoxy-thymidine diphosphate (dTDP)-rhamnose, a precursor of L-rhamnose, which has been shown to be required for virulence in several human pathogenic bacteria. Rhamnose is known to be a minor cell wall glycan in fungi and has therefore not been suspected as a crucial molecule in fungal-host interactions. Nevertheless, our study shows that deletion of the VdNRS/ER gene from the V. dahliae genome results in complete loss of pathogenicity on tomato and Nicotiana benthamiana plants, whereas vegetative growth and sporulation are not affected. We demonstrate that VdNRS/ER is a functional enzyme in the biosynthesis of uridine diphosphate (UDP)-rhamnose, and further analysis has revealed that VdNRS/ER deletion strains are impaired in the colonization of tomato roots. Collectively, our results demonstrate that rhamnose, although only a minor cell wall component, is essential for the pathogenicity of V. dahliae.
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708, PB, Wageningen, the Netherlands.
authors.forename: Parthasarathy
authors.initials: P
authors.lastname: Santhanam
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708, PB, Wageningen, the Netherlands.
authors.forename: Jordi C
authors.initials: JC
authors.lastname: Boshoven
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602, USA.
authors.forename: Omar
authors.initials: O
authors.lastname: Salas
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602, USA.
authors.forename: Kyle
authors.initials: K
authors.lastname: Bowler
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708, PB, Wageningen, the Netherlands.
authors.forename: Md Tohidul
authors.initials: MT
authors.lastname: Islam
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708, PB, Wageningen, the Netherlands.
authors.forename: Mojtaba Keykha
authors.initials: MK
authors.lastname: Saber
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708, PB, Wageningen, the Netherlands.
authors.forename: Grardy C M
authors.initials: GC
authors.lastname: van den Berg
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602, USA.
authors.forename: Maor
authors.initials: M
authors.lastname: Bar-Peled
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708, PB, Wageningen, the Netherlands.
authors.forename: Bart P H J
authors.initials: BP
authors.lastname: Thomma
mesh_terms: D002238:Carbohydrate Epimerases / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D021901:DNA, Intergenic / Q000235:genetics; D005656:Fungal Proteins / Q000378:metabolism*; D017353:Gene Deletion; D054884:Host-Pathogen Interactions / Q000235:genetics; D018551:Solanum lycopersicum / Q000382:microbiology; D016254:Mutagenesis, Insertional / Q000235:genetics; D010935:Plant Diseases / Q000382:microbiology*; D018517:Plant Roots / Q000382:microbiology; D058526:Plant Vascular Bundle / Q000382:microbiology*; D012210:Rhamnose / Q000378:metabolism; D013172:Spores, Fungal / Q000502:physiology; D014026:Nicotiana / Q000382:microbiology; D014170:Transformation, Genetic; D014530:Uridine Diphosphate / Q000378:metabolism; D020172:Verticillium / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence
chemical_list: D004269:DNA, Bacterial; D021901:DNA, Intergenic; D005656:Fungal Proteins; C036483:T-DNA; D014530:Uridine Diphosphate; D002238:Carbohydrate Epimerases; D012210:Rhamnose
keywords: Agrobacterium tumefaciens-mediated transformation (ATMT); UDP-rhamnose; attachment; carbohydrate; root colonization; tomato; vascular wilt