title: Structure, evolution and functional inference on the Mildew Locus O (MLO) gene family in three cultivated Cucurbitaceae spp.
abstract: BACKGROUND
  The powdery mildew disease affects thousands of plant species and arguably represents the major fungal threat for many Cucurbitaceae crops, including melon (Cucumis melo L.), watermelon (Citrullus lanatus L.) and zucchini (Cucurbita pepo L.). Several studies revealed that specific members of the Mildew Locus O (MLO) gene family act as powdery mildew susceptibility factors. Indeed, their inactivation, as the result of gene knock-out or knock-down, is associated with a peculiar form of resistance, referred to as mlo resistance.
  
  
  RESULTS
  We exploited recently available genomic information to provide a comprehensive overview of the MLO gene family in Cucurbitaceae. We report the identification of 16 MLO homologs in C. melo, 14 in C. lanatus and 18 in C. pepo genomes. Bioinformatic treatment of data allowed phylogenetic inference and the prediction of several ortholog pairs and groups. Comparison with functionally characterized MLO genes and, in C. lanatus, gene expression analysis, resulted in the detection of candidate powdery mildew susceptibility factors. We identified a series of conserved amino acid residues and motifs that are likely to play a major role for the function of MLO proteins. Finally, we performed a codon-based evolutionary analysis indicating a general high level of purifying selection in the three Cucurbitaceae MLO gene families, and the occurrence of regions under diversifying selection in candidate susceptibility factors.
  
  
  CONCLUSIONS
  Results of this study may help to address further biological questions concerning the evolution and function of MLO genes. Moreover, data reported here could be conveniently used by breeding research, aiming to select powdery mildew resistant cultivars in Cucurbitaceae.
authors.affiliation: Department of Agriculture Sciences, University of Naples 'Federico II', Via Università 100, 80055, Portici, Naples, Italy. paolo.iovieno@unina.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Iovieno
authors.affiliation: Department of Agriculture Sciences, University of Naples 'Federico II', Via Università 100, 80055, Portici, Naples, Italy. giuseppeandolfo@hotmail.com.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Andolfo
authors.affiliation: Institute of Biosciences and Bioresources, Italian National Council of Research, Via Amendola 165/A, 70126, Bari, Italy. gisella_s@libero.it.
authors.forename: Adalgisa
authors.initials: A
authors.lastname: Schiavulli
authors.affiliation: Institute of Biosciences and Bioresources, Italian National Council of Research, Via Amendola 165/A, 70126, Bari, Italy. domenico.catalano@ibbr.cnr.it.
authors.forename: Domenico
authors.initials: D
authors.lastname: Catalano
authors.affiliation: Department of Soil, Plant and Food Science, University of Bari "Aldo Moro", Via Amendola 165/A, 70126, Bari, Italy. luigi.ricciardi@uniba.it.
authors.forename: Luigi
authors.initials: L
authors.lastname: Ricciardi
authors.affiliation: Department of Agriculture Sciences, University of Naples 'Federico II', Via Università 100, 80055, Portici, Naples, Italy. luigi.frusciante@unina.it.
authors.forename: Luigi
authors.initials: L
authors.lastname: Frusciante
authors.affiliation: Department of Agriculture Sciences, University of Naples 'Federico II', Via Università 100, 80055, Portici, Naples, Italy. ercolano@unina.it.
authors.forename: Maria Raffaella
authors.initials: MR
authors.lastname: Ercolano
authors.affiliation: Department of Soil, Plant and Food Science, University of Bari "Aldo Moro", Via Amendola 165/A, 70126, Bari, Italy. stefano.pavan@uniba.it.
authors.forename: Stefano
authors.initials: S
authors.lastname: Pavan
mesh_terms: D001203:Ascomycota / Q000145:classification* / Q000502:physiology*; D019662:Cucurbitaceae / Q000235:genetics* / Q000382:microbiology*; D010802:Phylogeny; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D010940:Plant Proteins