Abstract
Guazatine is a potent inhibitor of polyamine oxidase (PAO) activity. In agriculture, guazatine is used as non-systemic contact fungicide efficient in the protection of cereals and citrus fruits against disease. The composition of guazatine is complex, mainly constituted by a mixture of synthetic guanidated polyamines (polyaminoguanidines). Here, we have studied the effects from exposure to guazatine in the weed Arabidopsis thaliana. We report that micromolar concentrations of guazatine are sufficient to inhibit growth of Arabidopsis seedlings and induce chlorosis, whereas germination is barely affected. We observed the occurrence of quantitative variation in the response to guazatine between 107 randomly chosen Arabidopsis accessions. This enabled us to undertake genome-wide association (GWA) mapping that identified a locus on chromosome one associated with guazatine tolerance. CHLOROPHYLLASE 1 (CLH1) within this locus was studied as candidate gene, together with its paralog (CLH2). The analysis of independent clh1-2, clh1-3, clh2-3, clh2-2, and double clh1-2 clh2-3 mutant alleles indicated that CLH1 and/or CLH2 loss-of-function or expression down-regulation promote guazatine tolerance in Arabidopsis. We report a natural mechanism by which Arabidopsis populations can overcome toxicity by the fungicide guazatine.
Highlights
Arabidopsis thaliana is a small weed mainly distributed in the northern hemisphere
Due to the use of polyaminoguanidines as fungicide in agriculture, we studied the effects of guazatine treatment in germination and growth of the weed Arabidopsis
We report the deleterious effects derived from the exposure to low (2.5 μM) concentrations of guazatine in Arabidopsis seedlings, the occurrence of extensive natural variation for guazatine tolerance traits in a set of 107 accessions, and the identification of genes involved in this response by genome-wide association (GWA) mapping
Summary
Arabidopsis thaliana (thereafter referred to as Arabidopsis) is a small weed mainly distributed in the northern hemisphere. It grows in open or recently disturbed habitats and its spread was facilitated by the expansion of agriculture (François et al, 2008). We have used genome-wide association studies (GWAS) to identify genes contributing to the natural variation in guazatine tolerance observed in this species. Multiple recombination events in the genetic history of populations produce close linkage disequilibrium (LD) of markers with causal loci for certain phenotypes. Such associations can be detected through GWAS.
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