title: Genome-Wide Study of the Tomato SlMLO Gene Family and Its Functional Characterization in Response to the Powdery Mildew Fungus Oidium neolycopersici.
abstract: The MLO (Mildew Locus O) gene family encodes plant-specific proteins containing seven transmembrane domains and likely acting in signal transduction in a calcium and calmodulin dependent manner. Some members of the MLO family are susceptibility factors toward fungi causing the powdery mildew disease. In tomato, for example, the loss-of-function of the MLO gene SlMLO1 leads to a particular form of powdery mildew resistance, called ol-2, which arrests almost completely fungal penetration. This type of penetration resistance is characterized by the apposition of papillae at the sites of plant-pathogen interaction. Other MLO homologs in Arabidopsis regulate root response to mechanical stimuli (AtMLO4 and AtMLO11) and pollen tube reception by the female gametophyte (AtMLO7). However, the role of most MLO genes remains unknown. In this work, we provide a genome-wide study of the tomato SlMLO gene family. Besides SlMLO1, other 15 SlMLO homologs were identified and characterized with respect to their structure, genomic organization, phylogenetic relationship, and expression profile. In addition, by analysis of transgenic plants, we demonstrated that simultaneous silencing of SlMLO1 and two of its closely related homologs, SlMLO5 and SlMLO8, confer higher level of resistance than the one associated with the ol-2 mutation. The outcome of this study provides evidence for functional redundancy among tomato homolog genes involved in powdery mildew susceptibility. Moreover, we developed a series of transgenic lines silenced for individual SlMLO homologs, which lay the foundation for further investigations aimed at assigning new biological functions to the MLO gene family.
authors: Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences Beijing, China.
authors: Zheng
authors: Z
authors: Zheng
authors: Wageningen UR Plant Breeding, Wageningen University and Research Centre Wageningen, Netherlands.
authors: Michela
authors: M
authors: Appiano
authors: Section of Genetics and Plant Breeding, Department of Plant, Soil and Food Science, University of Bari Aldo Moro Bari, Italy.
authors: Stefano
authors: S
authors: Pavan
authors: Section of Genetics and Plant Breeding, Department of Plant, Soil and Food Science, University of Bari Aldo Moro Bari, Italy.
authors: Valentina
authors: V
authors: Bracuto
authors: Section of Genetics and Plant Breeding, Department of Plant, Soil and Food Science, University of Bari Aldo Moro Bari, Italy.
authors: Luigi
authors: L
authors: Ricciardi
authors: Wageningen UR Plant Breeding, Wageningen University and Research Centre Wageningen, Netherlands.
authors: Richard G F
authors: RG
authors: Visser
authors: Wageningen UR Plant Breeding, Wageningen University and Research Centre Wageningen, Netherlands.
authors: Anne-Marie A
authors: AM
authors: Wolters
authors: Wageningen UR Plant Breeding, Wageningen University and Research Centre Wageningen, Netherlands.
authors: Yuling
authors: Y
authors: Bai
keywords: MLO gene family; powdery mildew disease; susceptibility; tomato