Abutilon theophrasti’s Root Associated Microorganisms Support Hydroxylation-dependent Benzoxazolinone Detoxification and Degradation

Abstract

Abutilon theophrasti is one of the most problematic weeds worldwide. Rye mulches, rich in benzoxazinoids, could not suppress Abutilon (Herbiseeds) due to its avoidance of high BOA/BOA detoxification product accumulation and phytotoxic 2-aminophenoxazinone production. Since Abutilon theophrasti seed coats harbour a variety of fungi and bacteria, a participation of those organisms in BOA degradation was assumed. The avoidance of high detoxification product/BOA accumulation in the roots was correlated with the presence of the Zygomycete Actinomucor elegans, which is known to colonize Abutilon seed coats. The microorganism(s) produced plant growth promoting compounds, whereby tryptophan excretion was stimulated by BOA. In Fenton reactions with BOA, tryptophan accelerates the destruction of the allelochemical via hydroxylated BOA molecules, when used in defined ratios. Destruction of BOA via hydroxylated molecules presents a new pathway for BOA degradation without accumulation of 2-aminophenoxazinone. During this process tryptophan is also degraded. Applications of high concentrations of tryptophan led, however, to a higher, channelled synthesis of BOA-6-O-glucoside in the roots, probably to slow down oxygen consuming Fenton reactions. From all possible hydroxylated BOA molecules, BOA-6-OH is the best substrate for Oglucosylation. Incubations in presence of the mono-oxygenase effector 2- bromo-4´-nitroacetophenone revealed that those enzymes are mainly responsible for BOA-6-OH synthesis and only a minor part results from Fenton reactions. The study elucidates the important role of plant-microorganism associations in the survival of allelopathic attacks