More than a fungicide: unravelling the beneficial effects of KM in plants

Abstract

The human global population is rising rapidly every year, increasing the demand for sustainable food production in modern climate change-striken agriculture. A greater understanding of how plants regulate their growth and unraveling the factors underpinning plant growth are therefore fundamental for crop yield improvement. Subsequently, finding strategies to optimize crop production as well as plant survival in the presence of abiotic stress factors is a task of crucial importance. The existence of chemical compounds with promising features resulting in plant growth promotion and enhanced tolerance to abiotic stress is attracting increasing attention. Strobilurins comprise an important class of fungicides applied in a range of plants that exert positive effects in plant fitness and physiology, frequently defined as “greening effect”. The central aim of this thesis was to unravel the underlying mechanisms responsible for the kresoxim-methyl (KM; a representative member of strobilurins)-induced growth promotion and enhanced stress tolerance. KM emerged to be a promising priming inducer by ameliorating the deleterious effects of salinity and drought in plants via the regulation of multiple cellular, biochemical and molecular processes. These promising results, and in particular, the effects observed in treated plants grown under optimal conditions were the driving force to subsequently examine the potential effects of KM as a plant growth promoting compound in greater depth. Application of KM by root watering, in its commercial formulation Stroby®-WG (BASF), resulted in a profound positive effect in Arabidopsis rosette growth by enhancing cell proliferation. Stroby-treated plants revealed differential expression of nitrate and sugar transporter as well as iron-related genes including the subgroup Ib basic helix-loop-helix (bHLH) transcription factors. bHLH039 in particular, was found to play a pivotal role in mediating Stroby-induced growth promotion. Pharmacological studies showed that nitric oxide (NO) was produced not only in the leaves but possibly in roots as well. The findings of the present thesis firmly support the notion that Stroby-mediated growth promotion is mainly a result of NO signaling function, which elicits downstream developmental processes. However, further research is needed to fully unravel the effect of Stroby in the root, focusing on the source and function of NO produced following Stroby treatment. Collectively, the findings of this thesis provide new insight in the mode of action of KM as a promising priming agent and growth promoting compound.