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

Helgard Kaufmann,Juliane Wehmeyer,Xianqin Qiu,Thomas Debener

doi:10.3389/fpls.2012.00244

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.

Highlights

Powdery mildew is one of the most serious rose diseases
Mildew resistance locus o genes have been identified in a number of species based on their sequence similarity to the well-characterized genes from barley and Arabidopsis (Yu et al, 2005; Feechan et al, 2008; Liu and Zhu, 2008; Cheng et al, 2012)
In addition to the first mildew resistance locus o (MLO) gene isolated from barley (Buschges et al, 1997), orthologs from Arabidopsis, tomato, and pea have been described (Consonni et al, 2006; Bai et al, 2008; Humphry et al, 2011; Pavan et al, 2011)

Summary

Introduction

Powdery mildew is one of the most serious rose diseases. Disease control is economically important for cut and pot roses, which are almost exclusively produced in greenhouses throughout temperate regions or at higher elevations in the tropics. The application of fungicides to combat powdery mildew is expensive and, in most parts of the world, increasingly limited by legal restrictions. These circumstances leave genetic strategies as the only environmentally friendly alternative for controlling disease. 3– 5 days after infection new conidiophores are formed completing the vegetative life cycle. In addition to the vegetative life cycle P. pannosa forms sexual spores in so-called“ascomata”under less favorable conditions. Infected leaves display distortions and often die but even mildly infected leaves reduce the esthetic value of a rose plants making cut and pot roses non-marketable

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