Fire blight resistance of the wild apple species Malus fusca: mapping, gene isolation and functional characterization
Final Report Abstract
Fire blight is the most devastating bacterial disease of the genus Malus. Caused by the pathogen, Erwinia amylovora, this disease is capable of destroying an entire apple (Malus domestica Borkh.) orchard within a single growing season with favourable conditions for the pathogen, thus resulting in economic damages worth millions of Euros. The most eco-friendly and sustainable means of tackling this menace is to breed fire blight resistant apples, however, most apple cultivars are susceptible which leaves the research community with the challenge of using already identified resistant sources from wild Malus species. Another challenge is the fact that resistance to fire blight is strain dependent with several reports of the complete breakdown of a few resistance gene sources identified in wild Malus species. The current project focused on the fire blight resistance of the wild apple species Malus fusca (accession MAL0045). A strong fire blight resistance locus on linkage group (LG) 10 (Mfu10) corresponding to chromosome 10 of the apple genome was initially reported. This locus was identified using a progeny population derived from M. fusca × ‘Idared’ cross and a moderately aggressive strain of E. amylovora, Ea222. The durability of this resistance was confirmed using a highly aggressive strain from Canada, Ea3049, which is responsible for the breakdown of the resistance of other Malus accessions, but not Mfu10 nor its donor MAL0045. Thus, the strength of Mfu10 was attributed to a major gene. Therefore, the aim of the current project was to continue studying the interaction of Mfu10 with several mutant strains of E. amylovora, develop a dense genetic linkage map of this crabapple using genotyping-by-sequencing (GBS) approach and search for novel minor loci in the genome, and ultimately identify the gene underlying Mfu10 on chromosome 10 and validate its function. We report here for the first time, the construction of a dense SNP map of M. fusca and the identification of a novel minor locus on LG16 (Mfu16) which contributes to the strong fire blight resistance in this wild species accession. In addition, the current project led to the identification of a candidate gene (FB_Mfu10) which underlies the resistance locus on chromosome 10. FB_Mfu10 is a receptor-like kinase (RLK) gene with 880 amino acids arranged in eight exons that encodes B-lectin and serine/threonine kinase domains known to be parts of genes conferring resistance to plant diseases. Furthermore, amplification of the open reading frame (ORF) of this gene on resistant and susceptible progenies and the subsequent sequencing of the amplicons led to the identification of 8 bp (base pair) insertion in the first exon that distinguishes resistance from susceptibility. When validated in future complementing studies, FB_Mfu10 will play a crucial role in the actualization of durable fire blight resistance in Malus as till date no wild type or mutant strain of the causal pathogen has been found able to breakdown its resistance. We speculate the plausibility of FB_Mfu10 conferring broad spectrum resistance to this very destructive disease of apples.
Publications
- (2015) The fire blight resistance QTL of Malus fusca (Mfu10) is affected but not broken down by the highly virulent Canadian Erwinia amylovora strain E2002A. European Journal of Plant Pathology 141, 631-635
Emeriewen OF, Richter K, Hanke M-V, Malnoy M, Peil A
(See online at https://doi.org/10.1007/s10658-014-0565-8) - (2017) Further insights into Malus fusca fire blight resistance. Journal of Plant Pathology
Emeriewen OF, Richter K, Hanke M-V, Malnoy M, Peil A
(See online at https://doi.org/10.4454/jpp.v99i0.3908) - (2018) Towards map-based cloning of FB_Mfu10: identification of a receptor-like kinase candidate gene underlying the Malus fusca fire blight resistance locus on linkage group 10. Molecular Breeding 38: 106
Emeriewen OF, Richter K, Piazza S, Micheletti D, Broggini GAL, Berner T, Keilwagen J, Hanke M-V, Malnoy M, Peil A
(See online at https://doi.org/10.1007/s11032-018-0863-5) - (2019) Malus hosts – Erwinia amylovora interactions: strain pathogenicity and resistance mechanisms. Frontiers in Plant Science 10: 551
Emeriewen OF, Wöhner T, Flachowsky H, Peil A
(See online at https://doi.org/10.3389/fpls.2019.00551)
