Analysis of the natural genetic variation of phosphite sensitivity in Arabidopsis thaliana

Phosphorus is one of the most critical macronutrients for plants and taken up from the soil in the form of phosphate (H2PO4-, Pi) by specific transporters. It is frequently a growth limiting factor due to low availability in the soil. Hence plants have developed adaptations to Pi starvation that include the alteration of root architecture and the secretion of organic acids to enhance Pi uptake capacity. Pi depleted plants also increase the expression of genes involved in Pi acquisition, e.g. Pi transporters and purple acid phosphatases. Phosphite (H2PO3-, Phi) is the reduced form of Pi and taken up by plants through phosphate transporters. Although metabolically inert, Phi is able to suppress some Pi-starvation responses which exacerbates Pi depletion leading to an inhibition of plant growth. In addition, Phi induces plant defence responses and effectively inhibits colonisation by oomycete pathogens (e.g. Phytophthora spp.). Although phosphite is the only reliable measure to control these pathogens, its mode of action remains unclear. To better understand the effects of Phi on plant growth and induced pathogen resistance we are analysing the genetic basis of Phi sensitivity in Arabidopsis thaliana. We have investigated the phenotypic responses of 18 Arabidopsis accessions and also EMS mutagenized lines to Phi treatment. This has led to the identification of a major QTL and also a mutant line with increased phosphite tolerance. Gene expression studies also reveal differences in the response of two contrasting accessions. The findings will improve our knowledge of the mode of phosphite action in plant defence responses, and may have implications for the understanding of Pi signalling or metabolism