Nutrient accumulation in Brassica: identification of new targets for crop improvement and biofortification

Plants require at least 14 essential mineral nutrients in order to successfully complete their life cycle. Nitrogen, phosphorus and potassium are required in particularly large quantities, and there is an ever increasing demand for fertiliser inputs to maintain adequate concentrations in crops. Humans are made up of at least 35 mineral nutrients, most of which originate from the ingestion of plant material. It is likely that much of the world’s population consumes insufficient quantities of numerous mineral nutrients, including calcium and magnesium. Variation in nutrient concentration traits in a diversity population of Brassica napus was characterised. Leaf nitrate, phosphorus, potassium, calcium and magnesium data, along with markers developed through transcriptome sequencing, were subsequently used to determine associated quantitative trait loci. Arabidopsis thaliana and Brassica genotypes mutated in selected candidate genes were characterised for nutrient concentration traits. An additional, EMS mutagenesis-background genotype, previously shown to accumulate magnesium, was also investigated. Both physiological and genetic bases of the trait were considered, including through leaf spatial-distribution mapping of mineral elements, and analysis of bulked-segregant DNA sequence data. Associative transcriptomics analyses identified numerous genetic loci and allelic variants for all traits investigated which may prove useful in marker-assisted selection strategies. Plants mutated in several calcium and magnesium accumulation candidate genes also have perturbed nutrient profiles. Characterisation of unique physiological traits in the magnesium accumulator mutant indicated drastic changes in tissue and cellular distribution of magnesium and phosphorus. Findings from this and other characterisation experiments enabled the identification of relatively few candidate genetic polymorphisms from DNA sequence data. This thesis has identified a number of new targets for controlling nutrient accumulation in Brassica spp. This knowledge could be applied in the development of novel crop varieties with greater nutrient-use efficiency and accumulation traits in order to decrease crop fertiliser requirements and reduce widespread human undernutrition.