title: Rather than by direct acquisition via lateral gene transfer, GHF5 cellulases were passed on from early Pratylenchidae to root-knot and cyst nematodes.
abstract: BACKGROUND
  Plant parasitic nematodes are unusual Metazoans as they are equipped with genes that allow for symbiont-independent degradation of plant cell walls. Among the cell wall-degrading enzymes, glycoside hydrolase family 5 (GHF5) cellulases are relatively well characterized, especially for high impact parasites such as root-knot and cyst nematodes. Interestingly, ancestors of extant nematodes most likely acquired these GHF5 cellulases from a prokaryote donor by one or multiple lateral gene transfer events. To obtain insight into the origin of GHF5 cellulases among evolutionary advanced members of the order Tylenchida, cellulase biodiversity data from less distal family members were collected and analyzed.
  
  
  RESULTS
  Single nematodes were used to obtain (partial) genomic sequences of cellulases from representatives of the genera Meloidogyne, Pratylenchus, Hirschmanniella and Globodera. Combined Bayesian analysis of ≈ 100 cellulase sequences revealed three types of catalytic domains (A, B, and C). Represented by 84 sequences, type B is numerically dominant, and the overall topology of the catalytic domain type shows remarkable resemblance with trees based on neutral (= pathogenicity-unrelated) small subunit ribosomal DNA sequences. Bayesian analysis further suggested a sister relationship between the lesion nematode Pratylenchus thornei and all type B cellulases from root-knot nematodes. Yet, the relationship between the three catalytic domain types remained unclear. Superposition of intron data onto the cellulase tree suggests that types B and C are related, and together distinct from type A that is characterized by two unique introns.
  
  
  CONCLUSIONS
  All Tylenchida members investigated here harbored one or multiple GHF5 cellulases. Three types of catalytic domains are distinguished, and the presence of at least two types is relatively common among plant parasitic Tylenchida. Analysis of coding sequences of cellulases suggests that root-knot and cyst nematodes did not acquire this gene directly by lateral genes transfer. More likely, these genes were passed on by ancestors of a family nowadays known as the Pratylenchidae.
authors.affiliation: Laboratory of Nematology, Department of Plant Sciences, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands. Kasia.Rybarczyk@wur.nl
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Rybarczyk-Mydłowska
authors.forename: Hazel Ruvimbo
authors.initials: HR
authors.lastname: Maboreke
authors.forename: Hanny
authors.initials: H
authors.lastname: van Megen
authors.forename: Sven
authors.initials: S
authors.lastname: van den Elsen
authors.forename: Paul
authors.initials: P
authors.lastname: Mooyman
authors.forename: Geert
authors.initials: G
authors.lastname: Smant
authors.forename: Jaap
authors.initials: J
authors.lastname: Bakker
authors.forename: Johannes
authors.initials: J
authors.lastname: Helder
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001499:Bayes Theorem; D044602:Cellulases / Q000235:genetics*; D019143:Evolution, Molecular; D022761:Gene Transfer, Horizontal; D007438:Introns; D016013:Likelihood Functions; D010802:Phylogeny; D018517:Plant Roots / Q000469:parasitology; D054730:Protein Interaction Domains and Motifs; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017187:Tylenchida / Q000201:enzymology / Q000235:genetics*
chemical_list: D044602:Cellulases