Naturally occurring broad-spectrum powdery mildew resistance in a Central American tomato accession is caused by loss of mlo function.
The resistant cherry tomato (Solanum lycopersicum var. cerasiforme) line LC-95, derived from an accession collected in Ecuador, harbors a natural allele (ol-2) that confers broad-spectrum and recessively inherited resistance to powdery mildew (Oidium neolycopersici). As both the genetic and phytopathological characteristics of ol-2-mediated resistance are reminiscent of powdery mildew immunity conferred by loss-of-function mlo alleles in barley and Arabidopsis, we initiated a candidate-gene approach to clone Ol-2. A tomato Mlo gene (SlMlo1) with high sequence-relatedness to barley Mlo and Arabidopsis AtMLO2 mapped to the chromosomal region harboring the Ol-2 locus. Complementation experiments using transgenic tomato lines as well as virus-induced gene silencing assays suggested that loss of SlMlo1 function is responsible for powdery mildew resistance conferred by ol-2. In progeny of a cross between a resistant line bearing ol-2 and the susceptible tomato cultivar Moneymaker, a 19-bp deletion disrupting the SlMlo1 coding region cosegregated with resistance. This polymorphism results in a frameshift and, thus, a truncated nonfunctional SlMlo1 protein. Our findings reveal the second example of a natural mlo mutant that possibly arose post-domestication, suggesting that natural mlo alleles might be evolutionarily short-lived due to fitness costs related to loss of mlo function.
Laboratory of Plant Breeding, Plant Sciences Group, Wageningen University, Droevendaalsesteeg 1, Wageningen, The Netherlands. bai.yuling@wur.nl
Yuling
Y
Bai
Stefano
S
Pavan
Zheng
Z
Zheng
Nana F
NF
Zappel
Anja
A
Reinstädler
Concetta
C
Lotti
Claudio
C
De Giovanni
Luigi
L
Ricciardi
Pim
P
Lindhout
Richard
R
Visser
Klaus
K
Theres
Ralph
R
Panstruga
D000595:Amino Acid Sequence; D001203:Ascomycota / Q000502:physiology*; D002489:Central America; D020090:Chromosome Segregation; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D005816:Genetic Complementation Test; D007113:Immunity, Innate / Q000276:immunology*; D007178:Inbreeding; D018551:Solanum lycopersicum / Q000235:genetics / Q000276:immunology* / Q000382:microbiology*; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010802:Phylogeny; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D010940:Plant Proteins; D012333:RNA, Messenger