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Multilocus Sequence Analysis of Selected Housekeeping- and Pathogenicity-Related Genes in Venturia inaequalis
Monika Michalecka1, Joanna Puławska1
1Department of Plant Protection, The National Institute of Horticultural Research, Konstytucji 3 Maja 1/3, 96-100 Skierniewice, Poland.
Abstract:
The relationship between housekeeping and pathogenicity-related genes and virulence or avirulence towards the primary Malus resistance genes (R) has not been previously studied for Venturia inaequalis fungus, the causal agent of apple scab. In this study, the sequences of two housekeeping genes encoding elongation factor alpha (EF-1α) and β-tubulin and two previously unstudied effector genes of V. inaequalis from mannosidase and glucosidase families of 100 strains collected from apple cultivars with Rvi6, Rvi1, and Rvi17 and without known scab resistance genes were submitted to the analyses. Based on the phylogenetic and diversity data, as well as recombination analyses of the sequenced regions, we assessed the phylogenetic relationships and genetic structure of the pathogen within the species and the evolutionary forces that are currently acting upon this microorganism. The topology of the obtained phylograms demonstrates the lack of a relationship between the phylogenetic position of the strain and the host cultivar and the geographical origin or race of the strain. The isolates from different hosts were differentiated but did not form diagnosable, distinct phylogenetic groups. These results suggest that the analyzed genes may be too conserved to reflect the adaptation of pathogens to apple genotypes with different R genes; thus, they do not adequately reflect race discrimination. In contrast, based on variation and gene flow estimation, genetic divergence was observed among strains virulent to apple trees containing Rvi6. The results of this study confirmed a lack of free recombination between strains and demonstrated that the analyzed regions are in linkage disequilibrium and contain non-random polymorphisms associated with the strain.
Insights
Genetic analysis of apple scab fungus (Venturia inaequalis) reveals conserved genes do not distinguish pathogen strains. However, genetic divergence was observed in strains virulent to specific apple resistance genes, like Rvi6.
Area of Science:
- Plant Pathology
- Fungal Genetics
- Molecular Evolution
Background:
- Apple scab, caused by Venturia inaequalis, poses a significant threat to apple production.
- The relationship between V. inaequalis virulence and host resistance genes (R genes) is complex and not fully understood.
- Housekeeping and effector genes in V. inaequalis have not been extensively studied in relation to pathogenicity and host R genes.
Purpose of the Study:
- To investigate the phylogenetic relationships and genetic structure of Venturia inaequalis strains.
- To assess the correlation between housekeeping and effector genes and the virulence of V. inaequalis against different Malus resistance genes (Rvi6, Rvi1, Rvi17).
- To understand the evolutionary forces shaping the genetic diversity of V. inaequalis.
Main Methods:
- Phylogenetic analysis of housekeeping genes (EF-1α, β-tubulin) and effector genes (mannosidase, glucosidase families) from 100 V. inaequalis strains.
- Recombination analyses and gene flow estimations.
- Comparison of genetic data with host apple cultivar resistance profiles (Rvi6, Rvi1, Rvi17).
Main Results:
- Phylogenetic analysis showed no clear relationship between strain phylogeny, host cultivar, geographical origin, or race.
- Conserved genes were insufficient for discriminating V. inaequalis races or their adaptation to specific apple R genes.
- Genetic divergence and variation were observed among strains virulent to apple trees carrying the Rvi6 resistance gene.
- Lack of free recombination and linkage disequilibrium were detected in the analyzed gene regions.
Conclusions:
- Conserved housekeeping and effector genes in V. inaequalis are not ideal for race discrimination against diverse apple resistance genes.
- Specific genetic divergence exists in V. inaequalis strains targeting particular apple resistance genes, such as Rvi6.
- The analyzed gene regions exhibit non-random polymorphisms, suggesting selection pressures related to virulence or avirulence.
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