Advances in genetic engineering have placed synthetic biology at a prime position to develop new products, materials, and services that could contribute to the 2030 UN Sustainable Development goals. These include novel materials for water purification, new bio-based products to replace toxic industrial chemicals, and engineered organisms for bioremediation. Supporting the development of synthetic biology initiatives in developing countries is needed to ensure these benefits are open to all.

Creating sustainable bioeconomies for the 21st century relies on optimizing the use of biological resources to improve agricultural productivity and create new products. Arbuscular mycorrhizae (phylum Glomeromycota) form symbiotic relationships with over 80% of vascular plants. In return for carbon, these fungi improve plant health and tolerance to environmental stress. This symbiosis is over 400 million years old and there are currently over 200 known arbuscular mycorrhizae, with dozens of new species described annually. Metagenomic sequencing of native soil communities, from species-rich meadows to mangroves, suggests biologically diverse habitats support a variety of mycorrhizal species with potential agricultural, medical, and biotechnological applications. This review looks at the effect of mycorrhizae on plant metabolism and how we can harness this symbiosis to improve crop health. I will first describe the mechanisms that underlie this symbiosis and what physiological, metabolic, and environmental factors trigger these plant-fungal relationships. These include mycorrhizal manipulation of host genetic expression, host mitochondrial and plastid proliferation, and increased production of terpenoids and jasmonic acid by the host plant. I will then discuss the effects of mycorrhizae on plant root and foliar secondary metabolism. I subsequently outline how mycorrhizae induce three key benefits in crops: defense against pathogen and herbivore attack, drought resistance, and heavy metal tolerance. I conclude with an overview of current efforts to harness mycorrhizal diversity to improve crop health through customized inoculum. I argue future research should embrace synthetic biology to create mycorrhizal chasses with improved symbiotic abilities and potentially novel functions to improve plant health. As the effects of climate change and anthropogenic disturbance increase, the global diversity of arbuscular mycorrhizal fungi should be monitored and protected to ensure this important agricultural and biotechnological resource for the future.

The rapid global conversion of biodiverse landscapes to intensively managed arable fields may decrease microbial diversity and threaten the long-term fertility of native soils. Previous laboratory and experimental studies provide conflicting results: some have recorded declines in overall microbial diversity and certain beneficial microorganisms under intensified cultivation while others report no change (or even increased) diversity. However, few studies have been carried out in actual agricultural fields. We analysed the soil metagenomic communities of 36 current and former grasslands in Oxfordshire, England using Illumina sequencing of the bacterial 16S and fungal ITS1 regions to examine how agricultural intensification alters native microbial communities and whether arable reversion can reverse these processes. We demonstrate that land-use change did not affect bacterial diversity or specific beneficial taxa (nitrogen-fixing bacteria and mycorrhizas). However, fungal diversity declined and certain microbiota known to be plant pathogens (e.g. Olpidium) were significantly more abundant on agriculturally improved fields. On sites where arable reversion took place, microbial communities were similar to those from unimproved grasslands although overall vegetation diversity and fungal richness was lower. The conservation of species-rich grasslands and their associated microbial diversity could therefore be a key resource for sustainable agriculture in the future.

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