The development of tools and resources for the identification of inhibitors of pigment biosynthetic pathways in the chloroplast.

Background. The global population is projected to increase by 30% to 9.2 billion in 2050. In order to feed this population a 70% increase in food production is required [1]. This increased production must occur with less land availability, less water, less energy input, fertilizers and chemicals. Herbicides will remain an essential component of integrated pesticide management practices; if food production is to meet demand. No new herbicides have been commercialised with a novel mode of action for over 30 years [3], hence the increased threat from resistance, and the need to be able to focus efforts on Modes of action (MOA) at an earlier stage in herbicide discovery.
Bleaching herbicides are designated as chemicals that cause white bleaching of green plant leaves. Their effectiveness resides in their ability to cause light-dependant generation of singlet oxygen which damages lipids, chlorophyll and proteins leading to plant death [4]. Bleaching herbicides are chemically diverse, which reflects the different chloroplastic biosynthetic pathways and the individual components within these pathways they effect. The common phenotypic traits between bleaching herbicides often causes confusion in assigning MOAs to specific herbicidal inhibitors. For example, Norflurazon, is an inhibitor of carotenoid biosynthesis, specifically the enzyme phytoene desaturase (PDS), [5]. Inhibition of PDS results in the precursor phytoene accumulating. However, phytoene can also accumulate in vegetative tissues from the inhibition of plastoquinone/tocopherol biosynthesis. This is because plastoquinone acts as a cofactor involved in phytoene desaturation.
Scientific rationale and importance. In this training programme, genetic resources, metabolite profiling procedures and in vitro assays will be developed to enable the differentiation and validation of different bleaching herbicides. The approach will tackle the biological question using new technologies and an interdisciplinary approach, involving chemistry, bioengineering and formulations for high-throughput compound screening. These methodologies that facilitate the elucidation of herbicidal MOA are essential for the rapid assessment and progression of novel chemistries, allowing large-scale screening when applied in the agro-industry.