Compartmentalisation: A strategy for optimising symbiosis and tradeoff management.

Funder: European Research Executive AgencyFunder: Gatsby Charitable Foundation; doi: http://dx.doi.org/10.13039/501100000324Funder: Bill and Melinda Gates Foundation; doi: http://dx.doi.org/10.13039/100000865Plant root architecture is developmentally plastic in response to fluctuating nutrient levels in the soil. Part of this developmental plasticity is the formation of dedicated root cells and organs to host mutualistic symbionts. Structures like nitrogen-fixing nodules serve as alternative nutrient acquisition strategies during starvation conditions. Some root systems can also form myconodules-globular root structures that can host mycorrhizal fungi. The myconodule association is different from the wide-spread arbuscular mycorrhization. This range of symbiotic associations provides different degrees of compartmentalisation, from the cellular to organ scale, which allows the plant host to regulate the entry and extent of symbiotic interactions. In this review, we discuss the degrees of symbiont compartmentalisation by the plant host as a developmental strategy and speculate how spatial confinement mitigates risks associated with root symbiosis.Gatsby Foundation, Bill and Melinda Gates Foundation, European Comissio

Compartmentalisation: A strategy for optimising symbiosis and tradeoff management.

Plant root architecture is developmentally plastic in response to fluctuating nutrient levels in the soil. Part of this developmental plasticity is the formation of dedicated root cells and organs to host mutualistic symbionts. Structures like nitrogen-fixing nodules serve as alternative nutrient acquisition strategies during starvation conditions. Some root systems can also form myconodules-globular root structures that can host mycorrhizal fungi. The myconodule association is different from the wide-spread arbuscular mycorrhization. This range of symbiotic associations provides different degrees of compartmentalisation, from the cellular to organ scale, which allows the plant host to regulate the entry and extent of symbiotic interactions. In this review, we discuss the degrees of symbiont compartmentalisation by the plant host as a developmental strategy and speculate how spatial confinement mitigates risks associated with root symbiosis.Gatsby Foundation, Bill and Melinda Gates Foundation, European Comissio

GA dynamics governing nodulation revealed using GIBBERELLIN PERCEPTION SENSOR 2 in Medicago truncatula lateral organs.

During nutrient scarcity, plants can adapt their developmental strategy to maximize their chance of survival. Such plasticity in development is underpinned by hormonal regulation, which mediates the relationship between environmental cues and developmental outputs. In legumes, endosymbiosis with nitrogen fixing bacteria (rhizobia) is a key adaptation for supplying the plant with nitrogen in the form of ammonium. Rhizobia are housed in lateral root-derived organs termed nodules that maintain an environment conducive to Nitrogenase in these bacteria. Several phytohormones are important for regulating the formation of nodules, with both positive and negative roles proposed for gibberellin (GA). In this study, we determine the cellular location and function of bioactive GA during nodule organogenesis using a genetically-encoded second generation GA biosensor, GIBBERELLIN PERCEPTION SENSOR 2 in Medicago truncatula. We find endogenous bioactive GA accumulates locally at the site of nodule primordia, increasing dramatically in the cortical cell layers, persisting through cell divisions and maintaining accumulation in the mature nodule meristem. We show, through mis-expression of GA catabolic enzymes that suppress GA accumulation, that GA acts as a positive regulator of nodule growth and development. Furthermore, increasing or decreasing GA through perturbation of biosynthesis gene expression can increase or decrease the size of nodules, respectively. This is unique from lateral root formation, a developmental program that shares common organogenesis regulators. We link GA to a wider gene regulatory program by showing that nodule-identity genes induce and sustain GA accumulation necessary for proper nodule formation.ERC H2020, European Molecular Biology Organization Gatsby Charitable trust, Bill and Melinda Gates Foundation, UK Foreign, Commonwealth and Development Offic

Establishment of Expression in the SHORTROOT-SCARECROW Transcriptional Cascade through Opposing Activities of Both Activators and Repressors

Tissue-specific gene expression is often thought to arise from spatially restricted transcriptional cascades. However, it is unclear how expression is established at the top of these cascades in the absence of pre-existing specificity. We generated a transcriptional network to explore how transcription factor expression is established in the Arabidopsis thaliana root ground tissue. Regulators of the SHORTROOT-SCARECROW transcriptional cascade were validated in planta. At the top of this cascade, we identified both activators and repressors of SHORTROOT. The aggregate spatial expression of these regulators is not sufficient to predict transcriptional specificity. Instead, modeling, transcriptional reporters, and synthetic promoters support a mechanism whereby expression at the top of the SHORTROOT-SCARECROW cascade is established through opposing activities of activators and repressors

Establishment of Expression in the SHORTROOT-SCARECROW Transcriptional Cascade through Opposing Activities of Both Activators and Repressors

Tissue-specific gene expression is often thought to arise from spatially restricted transcriptional cascades. However, it is unclear how expression is established at the top of these cascades in the absence of pre-existing specificity. We generated a transcriptional network to explore how transcription factor expression is established in the Arabidopsis thaliana root ground tissue. Regulators of the SHORTROOT-SCARECROW transcriptional cascade were validated in planta. At the top of this cascade, we identified both activatorsand repressors ofSHORTROOT. The aggregate spatial expression of these regulators is not sufficient to predict transcriptional specificity. Instead, modeling, transcriptional reporters, and synthetic promoters support a mechanism whereby expression at the top of the SHORTROOT-SCARECROW cascade is established through opposing activities of activators and repressors