Resistance mechanism to carboxylic acid amide fungicides in the cucurbit downy mildew pathogen Pseudoperonospora cubensis

Abstract

Point mutations in the CesA3 gene of P. cubensis lead to CAA resistance. Accurate monitoring of these mutations among P. cubensis populations may improve/facilitate adequate recommendation/deployment of fungicides in the field.

The cellulose synthase 3 (CesA3) gene of oomycetes: structure, phylogeny and influence on sensitivity to carboxylic acid amide (CAA) fungicides

“…The conserved Pleckstrin Homology (PH) domain (cd00821, http://www.ncbi.nlm.nih.gov/Structure/cdd/wrpsb.cgi) at the N-terminus that has been identified in oomycete homologues of CesA1, CesA2 and CesA4 (Grenville-Briggs et al 2008;Fugelstad et al 2009;Blum et al 2010b;Blum et al 2011) was absent in all CesA3 sequences (Fig 1). However, instead of the PH domain, a CesA3 specific N-terminal domain containing two CxxC motifs occurred (Supplementary Fig 3B).…”

“…Since changes in the amino acid sequence of the CesA3 target enzyme at position 1105 and 1109 can affect CAA fungicide activity (Blum et al 2010b;Blum et al 2011;Chen et al 2011;Sierotzki et al 2011), the CesA3 sequences of 21 oomycete species that were tested in this study and four additional sequences (accessed from the NCBI database; Accession No. in Table 1) were aligned to analyze whether specific amino acid configurations in the putative target site correlated to fungicidal response.…”

“…However, single amino acid exchanges in CesA3 have been detected, conferring resistance to CAA fungicides in different plant pathogens of the Peronosporales such as P. infestans (Blum et al 2010a), Phytophthora capsici, Phytophthora melonis (Chen et al 2011), Plasmopara viticola (Blum et al 2010b), and Pseudoperonospora cubensis . In most cases, resistance was based on a single point mutation in the CesA3 gene, leading to a change at amino acid position 1105 from a conserved glycine to either alanine, serine, valine or tryptophan (G1105A, G1105S, G1105V, G1105W) (Blum et al 2010a;Blum et al 2010b;Blum et al 2011;Sierotzki et al 2011). In artificially generated mutants of P. infestans, P. capsici and P. melonis, a change from valine to leucine or methionine at position 1109 (V1109L, V1109M) also confers resistance to CAAs (Chen et al 2011, Syngenta internal data).…”

“…In oomycetes and plants, the machinery responsible for cellulose formation is a membrane bound enzyme complex (Paredez et al 2006;GrenvilleBriggs et al 2008) probably composed of several distinct cellulose synthase (CesA) subunits (Desprez et al 2007;Persson et al 2007). In oomycetes, up to four CesA encoding genes have been identified in Peronosporales, Pythiales and Saprolegniales (Grenville-Briggs et al 2008;Fugelstad et al 2009;Blum et al 2010b;Levesque et al 2010;Blum et al 2011); and their direct involvement in cellulose biosynthesis was demonstrated using RNA interference in P. infestans (Grenville-Briggs et al 2008). Out of the four CesAs, the CesA3 gene was most strongly expressed during mycelial growth of Phytophthora, Saprolegnia and Pythium species (GrenvilleBriggs et al 2008;Fugelstad et al 2009; indicating that it is of particular importance for the formation of cellulose in oomycetes.…”

“…In those species, little is also known about the existence of the CesA3 gene and its corresponding protein structure the configuration of which is suggested to affect sensitivity to CAAs. So far, the CesA3 gene has been described only in few oomycetes belonging to the Peronosporales, Pythiales and Saprolegniales (Grenville-Briggs et al 2008;Fugelstad et al 2009;Blum et al 2010b;Levesque et al 2010;Blum et al 2011), thus, the present study aimed to isolate and characterize the CesA3 gene in species from all six "crown" oomycete orders (Beakes & Sekimoto 2009). We identified the CesA3 gene in 14 different species of 11 genera, belonging to the six orders Albuginales, Leptomitales, Peronosporales, Pythiales, Rhipidiales and Saprolegniales.…”