Antisense expression of peach mildew resistance locus O (PpMlo1) gene confers cross-species resistance to powdery mildew in Fragaria x ananassa
Powdery mildew (PM) is one of the major plant pathogens. The conventional method of PM control includes frequent use of sulfur-based fungicides adding to production costs and potential harm to the environment. PM remains a major scourge for Rosaceae crops where breeding approaches mainly resort to gene-for-gene resistance. We have tested an alternate source of PM resistance in Rosaceae. Mildew resistance locus O (MLO) has been well studied in barley due to its role in imparting broad spectrum resistance to PM. We identified PpMlo1 (Prunus persica Mlo) in peach and characterized it further to test if a similar mechanism of resistance is conserved in Rosaceae. Due to its recalcitrance in tissue culture, reverse genetic studies involving PpMloI were not feasible in peach. Therefore, Fragaria x ananassa LF9 line, a taxonomic surrogate, was used for functional analysis of PpMlo1. Agrobacterium-mediated transformation yielded transgenic strawberry plants expressing PpMlo1 in sense and antisense orientation. Antisense expression of PpMlo1 in transgenic strawberry plants conferred resistance to Fragaria-specific powdery mildew, Podosphaera macularis. Phylogenetic analysis of 208 putative Mlo gene copies from 35 plant species suggests a large number of duplications of this gene family prior to the divergence of monocots and eudicots, early in eudicot diversification. Our results indicate that the Mlo-based resistance mechanism is functional in Rosaceae, and that Fragaria can be used as a host to test mechanistic function of genes derived from related tree species. To the best of our knowledge, this work is one of the first attempts at testing the potential of using a Mlo-based resistance strategy to combat powdery mildew in Rosaceae.
KeywordsRosaceae Powdery mildew Peach Fragaria Mildew locus O
This work was supported by Washington State University start-up funds to DM and AD. The authors would like to thank Albert G. Abbott, Donna Lalli, Tatyana Zhebentyayeva and Chris Saski at Clemson University for useful discussions and BAC sequencing; Kevin Folta at University of Florida for the Fragaria x ananassa LF9 line; Washington State University colleagues Patrick Moore for providing Fragaria-virulent powdery mildew Podosphaera macularis, Frank Dugan for discussions on pathogen challenge experiments and Pat Okubara for her advice on quantifying pathogen infection. Authors would like to acknowledge the assistance of Nathan Tarlyn in the AD laboratory for maintenance of plants used in this study.
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