Monocot and dicot MLO powdery mildew susceptibility factors are functionally conserved in spite of the evolution of class-specific molecular features.
BACKGROUND
Specific members of the plant Mildew Locus O (MLO) protein family act as susceptibility factors towards powdery mildew (PM), a worldwide-spread fungal disease threatening many cultivated species. Previous studies indicated that monocot and dicot MLO susceptibility proteins are phylogenetically divergent.


METHODS
A bioinformatic approach was followed to study the type of evolution of Angiosperm MLO susceptibility proteins. Transgenic complementation tests were performed for functional analysis.


RESULTS
Our results show that monocot and dicot MLO susceptibility proteins evolved class-specific conservation patterns. Many of them appear to be the result of negative selection and thus are likely to provide an adaptive value. We also tested whether different molecular features between monocot and dicot MLO proteins are specifically required by PM fungal species to cause pathogenesis. To this aim, we transformed a tomato mutant impaired for the endogenous SlMLO1 gene, and therefore resistant to the tomato PM species Oidium neolycopersici, with heterologous MLO susceptibility genes from the monocot barley and the dicot pea. In both cases, we observed restoration of PM symptoms. Finally, through histological observations, we demonstrate that both monocot and dicot susceptibility alleles of the MLO genes predispose to penetration of a non-adapted PM fungal species in plant epidermal cells.


CONCLUSIONS
With this study, we provide insights on the evolution and function of MLO genes involved in the interaction with PM fungi. With respect to breeding research, we show that transgenic complementation assays involving phylogenetically distant plant species can be used for the characterization of novel MLO susceptibility genes. Moreover, we provide an overview of MLO protein molecular features predicted to play a major role in PM susceptibility. These represent ideal targets for future approaches of reverse genetics, addressed to the selection of loss-of-function resistant mutants in cultivated species.
Wageningen UR Plant Breeding, Wageningen University & Research Centre, Droevendaalsesteeg 1, 6708, PB, Wageningen, The Netherlands.
Michela
M
Appiano
Institute of Biosciences and Bioresources, Italian National Research Council, via Amendola 165/A, 70126, Bari, Italy.
Domenico
D
Catalano
Wageningen UR Plant Breeding, Wageningen University & Research Centre, Droevendaalsesteeg 1, 6708, PB, Wageningen, The Netherlands.
Miguel
M
Santillán Martínez
Department of Agricultural, Food and Environmental Sciences, University of Foggia, Via Napoli 25, 71100, Foggia, Italy.
Concetta
C
Lotti
Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, No. 12 Zhongguan Cun Nan Da Jie, 100081, Beijing, China.
Zheng
Z
Zheng
Wageningen UR Plant Breeding, Wageningen University & Research Centre, Droevendaalsesteeg 1, 6708, PB, Wageningen, The Netherlands.
Richard G F
RG
Visser
Department of Soil, Plant and Food Science, Section of Genetics and Plant Breeding, University of Bari, Via Amendola 165/A, 70126, Bari, Italy.
Luigi
L
Ricciardi
Wageningen UR Plant Breeding, Wageningen University & Research Centre, Droevendaalsesteeg 1, 6708, PB, Wageningen, The Netherlands. bai.yuling@wur.nl.
Yuling
Y
Bai
Department of Soil, Plant and Food Science, Section of Genetics and Plant Breeding, University of Bari, Via Amendola 165/A, 70126, Bari, Italy. stefano.pavan@uniba.it.
Stefano
S
Pavan
D000595:Amino Acid Sequence; D001203:Ascomycota / Q000502:physiology*; D017124:Conserved Sequence; D060467:Disease Resistance / Q000235:genetics*; D004198:Disease Susceptibility; D019143:Evolution, Molecular; D017343:Genes, Plant; D056426:Genetic Loci; D054884:Host-Pathogen Interactions / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology*; D010940:Plant Proteins / Q000737:chemistry; D010944:Plants / Q000382:microbiology*; D030821:Plants, Genetically Modified
D010940:Plant Proteins