Maize synthesized benzoxazinoids affect the host associated microbiome

Abstract

Background: Plants actively shape their associated microbial communities by synthesizing bio-active substances. Plant secondary metabolites are known for their signaling and plant defense functions, yet little is known about their overall effect on the plant microbiome. In this work, we studied the effects of benzoxazinoids (BXs), a group of secondary metabolites present in maize, on the host-associated microbial structure. Using BX knockout mutants and their W22 parental lines, we employed 16S and ITS2 rRNA gene amplicon analysis to characterize the maize microbiome at early growth stages. Results: Rhizo-box experiment showed that BXs affected microbial communities not only in roots and shoots, but also in the rhizosphere. Fungal richness in roots was more affected by BXs than root bacterial richness. Maize genotype (BX mutants and their parental lines) as well as plant age explained both fungal and bacterial community structure. Genotypic effect on microbial communities was stronger in roots than in rhizosphere. Diverse, but specific, microbial taxa were affected by BX in both roots and shoots, for instance, many plant pathogens were negatively correlated to BX content. In addition, a co-occurrence analysis of the root microbiome revealed that BXs affected specific groups of the microbiome. Conclusions: This study provides insights into the role of BXs for microbial community assembly in the rhizosphere and in roots and shoots. Coupling the quantification of BX metabolites with bacterial and fungal communities, we were able to suggest a gatekeeper role of BX by showing its correlation with specific microbial taxa and thus providing insights into effects on specific fungal and bacterial taxa in maize roots and shoots. Root microbial cooccurrence networks revealed that BXs affect specific microbial clusters.

Comparative transcriptomic and metabolic analysis of wild and domesticated wheat genotypes reveals differences in chemical and physical defense responses against aphids

“…A recent study reported that the molecular functions of the BXDs are diverse beyond their toxicity. It was suggested that the BXDs function in shaping the root microbiome by selectively attracting the plant-beneficial rhizobacterium Pseudomonas putida [90,91], and are also used as iron chelators [92]. Also, it has been estimated that naturally occurring DIMBOA may govern a physical defense mechanism against aphid feeding by the accumulation of callose [93].…”

A footprint of plant eco-geographic adaptation on the composition of the barley rhizosphere bacterial microbiota

“…Likewise, this scenario is compatible with a limited number of genes controlling the biosynthesis and rhizodeposition of defensive secondary metabolites which have been implicated in shaping the plant microbiota 44 . Among these compounds, the indol-alkaloids benzoxazinoids recently gained centre-stage as master regulators of the maize-associated microbial communities 45–47 . Interestingly, Hordeum vulgare has evolved a distinct indol-alkaloid compound, gramine 48 , which is preferentially accumulated in the tissues of the wild genotypes compared to ‘Elite’ varieites 49 and whose physiological properties are comparable to the ones of benzoxazinoids 50 .…”

Impacts of Root Metabolites on Soil Nematodes

“…Meanwhile, the extrapolation of results obtained in vitro to rhizosphere and in planta conditions is not straightforward. For many compounds, information about their concentrations in roots, and in particular in rhizosphere soil, is sparse, and the concentration in the rhizosphere may easily be 1000 times lower than in the roots (Kudjordjie et al, 2019). We thus emphasize that effects detected at low concentrations, i.e.…”