Isolation, Molecular Characterization, and Mapping of Four Rose MLO Orthologs

Abstract

Powdery mildew is a major disease of economic importance in cut and pot roses. As an alternative to conventional resistance breeding strategies utilizing single-dominant genes or QTLs, mildew resistance locus o (MLO)-based resistance might offer some advantages. In dicots such as Arabidopsis, pea, and tomato, loss-of-function mutations in MLO genes confer high levels of broad-spectrum resistance. Here, we report the isolation and characterization of four MLO homologs from a large rose EST collection isolated from leaves. These genes are phylogenetically closely related to other dicot MLO genes that are involved in plant powdery mildew interactions. Therefore, they are candidates for MLO genes involved in rose powdery mildew interactions. Two of the four isolated genes contain all of the sequence signatures considered to be diagnostic for MLO genes. We mapped all four genes to three linkage groups and conducted the first analysis of alternative alleles. This information is discussed in regards to a reverse genetics approach aimed at the selection of rose plants that are homozygous for loss-of-function in one or more MLO genes.

Roses Exhibit Pathotype‐specific Resistance Responses to Powdery Mildew

“…It is probable that the molecular mechanism is common in more dicotyledonous and monocotyledonous plants. In rose, MLO orthologs are found in an EST library (Kaufmann et al 2012). Recessive inherited mlo (loss-of-function) mediates broad-spectrum resistance in these species at the preinvasive stage and leads to early termination of pathogenesis (H€ uckelhoven and Pangstruga 2011).…”

Expression Pattern Analysis of Four Mlo Genes from Rose

“…Primer sequence (5#-3#) UNAFold (version 3.4; RNA Institute, Albany, NY) software (Bustin et al, 2009). Because each rose Mlo gene has more than one allele (Kaufmann et al, 2012), the primers for each Mlo gene were designed to match only one allele (their sequences are the same as GenBank no. JX847131-JX847134) using Beacon Designer (version 8.0; Premier Biosoft International, Palo Alto, CA) software with the following specifications: optimal annealing temperature at 58 ± 2°C, optimal primer length of 18-24 nucleotides, optimal amplicon length of 80-300 bp, content of guanine and cytosine between 45% and 55%.…”

“…So far, four Mlo homologs RhMLO1-RhMLO4 were isolated from rose leaves (Kaufmann et al, 2012). Phylogenetic analysis showed that all Mlo genes from dicots for which a function in powdery mildew-host interaction has been experimentally demonstrated fall into one phylogenetic clade.…”

“…Phylogenetic analysis showed that all Mlo genes from dicots for which a function in powdery mildew-host interaction has been experimentally demonstrated fall into one phylogenetic clade. The clade consists of two smaller clades, one consists of rose genes RhMLO3 and 4, and the arabidopsis genes AtMLO2, 6, and 12; the other consists of rose genes RhMLO1 and 2, and pea gene PsMLO2 (Kaufmann et al, 2012). All four rose genes fall into the dicot cluster for powdery mildew-related Mlos and are therefore candidate Mlo orthologs.…”

Identification and Expression Analysis of Fragaria Vesca MLO Genes Involved in Interaction with Powdery Mildew (Podosphaera Aphanis)

“…An MLO gene was first identified in barley [3] and currently, a varying number of MLO genes have been identified in Arabidopsis, Medicago truncatula, chickpea, rice, maize, wheat, soybean, cucumber, tomato, rose, grapevine, peach, apple, sweet orange, cultivated Solanaceae, Brachypodium, and Cucurbitaceae species respectively [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Although the biological functions of MLO genes are not yet completely known, they act as suppressors of defense responses.…”