Genetic analysis of phosphite sensitivity in Arabidopsis thaliana

Daniel Kollehn

Application of phosphite to plants is used to manage oomycete diseases. However, the mode of action is not fully understood and together with a lack of alternative control methods, and increased resistance to phosphite, an in-depth investigation was warranted. Arabidopsis thaliana was used as a model to investigate the response to phosphite by looking at changes to relevant genes by ethyl methanesulphonate mutant analysis and by natural genetic variation between accessions. The ethyl methanesulphonate analysis resulted in a phosphite tolerant mutant with a significantly altered root phenotype. However, this was lost after out- and backcrosses and hence the mutation remains unknown. The presence of natural genetic variation between different accessions was shown and highlights that the phosphate starvation response can be used to investigate responses to phosphite. Notably, this study was the first to examine long-term exposure to phosphite in A. thaliana, allowing phosphate usage efficiency instead of variation on phosphate/phosphite uptake competition to be examined in detail. Out of 18 accessions screened, two contrasting accessions Bur-0 and Col-0 were shown to be suitable to investigate genetic variation, leading to the identification of highly significant quantitative trait loci’s. In turn, locally acting phosphate distribution and recycling genes were shown to respond differently to phosphite between accessions. These candidate genes were further investigated and hypothesised to increase phosphate use efficiency resulting in better plant growth. This study confirmed differences in the sensing and the distinction between phosphate and phosphite between accessions. Furthermore, the phosphate and phosphite status of the vacuole in the shoot and selective sequestration was shown to be involved in systematic phosphate starvation response regulation and signalling of adaptations in root development. Additionally, the highest measured gene induction was measured for the Pathogen Resistance1 gene in Col-0, proving a direct link between phosphate starvation response and pathogen defence. This further underlines the appropriateness of phosphite application against oomycete pathogens.

Genetic analysis of phosphite sensitivity in Arabidopsis thaliana

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