The mysterious non‐arbuscular mycorrhizal status of Brassicaceae species

Abstract

The Brassicaceae family is unique in not fostering functional symbiosis with arbuscular mycorrhiza (AM). The family is also special in possessing glucosinolates, a class of secondary metabolites predominantly functioning for plant defence. We have reviewed what effect the glucosinolates of this non-symbiotic host have on AM or vice versa. Isothiocyanates, the toxic degradation product of the glucosinolates, particularly the indolic and benzenic glucosinolates, are known to be involved in the inhibition of AM. Interestingly, AM colonization enhances glucosinolate production in two AM-host in the Brassicales family-Moringa oleifera and Tropaeolum spp. PHOSPHATE STARVATION RESPONSE 1 (PHR1), a central transcription factor that controls phosphate starvation response also activates the glucosinolate biosynthesis in AM non-host Arabidopsis thaliana. Recently, the advances in whole-genome sequencing, enabling extensive ecological microbiome studies have helped unravel the Brassicaceae microbiome, identifying new mutualists that compensate for the loss of AM symbiosis, and reporting cues for some influence of glucosinolates on the microbiome structure. We advocate that glucosinolate is an important candidate in determining the mycorrhizal status of Brassicaceae and has played a major role in its symbiosis-defence trade-off. We also identify key open questions in this area that remain to be addressed in the future.

Reviewing ecological implications of mycorrhizal fungal interactions in the Brassicaceae

“…The functions of these proteins must be definitively ascertained before causation can be ascribed. An analysis outlined in Sharma et al (2022) utilizing OrthoFinder (Emms and Kelly, 2015) found that of 14 AM symbiosis-specific genes nine putative orthologs were identified in proteome data of four members of the Brassicaceae. Similarly, of 11 common symbiotic pathway genes six putative orthologs were found, BOX 1 Arabidopsis thaliana.…”

“…This interaction may provide a roadmap to better understanding the function of mycorrhizal interactions with members of the Brassicaceae as well as fungal perception by would be plant partners. Trautwig et al 10.3389/fpls.2023.1269815 leading the authors to conclude that the absence of common symbiotic pathway genes may not be the sole reason for a lack of AM fungal association with the Brassicaceae (Sharma et al, 2022).…”

Editorial: Mycorrhizal fungi and plants in terrestrial ecosystems, volume II

“…However, there are some angiosperms that do not form AM symbiosis. Among these non-host species members of Brassicaceae are believed to be a non-host for arbuscular mycorrhizal fungi (AMF), because they produce isothiocyanates that are involved in inhibiting arbuscular mycorrhizal symbiosis (Sharma et al, 2023). This view has been challenged by a study of Floc'h et al in canola (Brassica napus L.), an important commodity crop.…”