Mandipropamid targets the cellulose synthase‐like PiCesA3 to inhibit cell wall biosynthesis in the oomycete plant pathogen, Phytophthora infestans

Abstract

Oomycete plant pathogens cause a wide variety of economically and environmentally important plant diseases. Mandipropamid (MPD) is a carboxylic acid amide (CAA) effective against downy mildews, such as Plasmopara viticola on grapes and potato late blight caused by Phytophthora infestans. Historically, the identification of the mode of action of oomycete-specific control agents has been problematic. Here, we describe how a combination of biochemical and genetic techniques has been utilized to identify the molecular target of MPD in P. infestans. Phytophthora infestans germinating cysts treated with MPD produced swelling symptoms typical of cell wall synthesis inhibitors, and these effects were reversible after washing with H(2)O. Uptake studies with (14)C-labelled MPD showed that this oomycete control agent acts on the cell wall and does not enter the cell. Furthermore, (14)C glucose incorporation into cellulose was perturbed in the presence of MPD which, taken together, suggests that the inhibition of cellulose synthesis is the primary effect of MPD. Laboratory mutants, insensitive to MPD, were raised by ethyl methane sulphonate (EMS) mutagenesis, and gene sequence analysis of cellulose synthase genes in these mutants revealed two point mutations in the PiCesA3 gene, known to be involved in cellulose synthesis. Both mutations in the PiCesA3 gene result in a change to the same amino acid (glycine-1105) in the protein. The transformation and expression of a mutated PiCesA3 allele was carried out in a sensitive wild-type isolate to demonstrate that the mutations in PiCesA3 were responsible for the MPD insensitivity phenotype.

Differences in the efficacy of carboxylic acid amide fungicides against less sensitive strains of Plasmopara viticola

“…2 The mutations conferring CAA resistance are G1105S and G1105V in the CesA3 gene. 3 CAA resistance is inherited in a recessive manner.…”

Mancozeb: Its Value to the EU Potato Industry

“…Widespread failures in control could occur in the future, due to resistance development, with yield losses from untreated P. infestans ranging from 10%-50% depending on infection severity and timing [12]. Although the cost to consumers was not directly calculated, an increase in cost of production and reduction in availability of supply are expected to lead to increased consumer costs.…”

EMS and UV irradiation induce unstable resistance against CAA fungicides in Bremia lactucae

“…Cellulose synthesis is crucial for germ-tube development in oomycetes and hence for infection (Blum et al 2010c). CAA fungicides were shown to inhibit cellulose biosynthesis, interfering with cellulose synthase, and avoiding germ-tube development and infection (Blum et al 2010c). A mutation at SNP 1105 of CesA3 alters the protein making it insensitive to CAAs, thus allowing spore germination and infection in the presence of CAAs (Blum et al 2010a, b).…”

“…We assume that the failure of B. lactucae to continue growing on CAA-treated plants at subsequent generations after mutagenesis, as well as the failure to bring resistance to homozygosity, resulted from the lack of mutation in the CesA3 gene. Cellulose synthesis is crucial for germ-tube development in oomycetes and hence for infection (Blum et al 2010c). CAA fungicides were shown to inhibit cellulose biosynthesis, interfering with cellulose synthase, and avoiding germ-tube development and infection (Blum et al 2010c).…”