Tunable control of insect pheromone biosynthesis in Nicotiana benthamiana

Engineering Nicotiana benthamiana for chrysoeriol production using synthetic biology approaches

Flavonoids are prevalent plant secondary metabolites with a broad range of biological activities. Their antioxidant, anti-inflammatory, and anti-cancer activities make flavonoids widely useful in a variety of industries, including the pharmaceutical and health food industries. However, many flavonoids occur at only low concentrations in plants, and they are difficult to synthesize chemically due to their structural complexity. To address these difficulties, new technologies have been employed to enhance the production of flavonoids in vivo. In this study, we used synthetic biology techniques to produce the methylated flavone chrysoeriol in Nicotiana benthamiana leaves. The chrysoeriol biosynthetic pathway consists of eight catalytic steps. However, using an Agrobacterium-mediated transient expression assay to examine the in planta activities of genes of interest, we shortened this pathway to four steps catalyzed by five enzymes. Co-expression of these five enzymes in N. benthamiana leaves resulted in de novo chrysoeriol production. Chrysoeriol production was unaffected by the Agrobacterium cell density used for agroinfiltration and increased over time, peaking at 10 days after infiltration. Chrysoeriol accumulation in agroinfiltrated N. benthamiana leaves was associated with increased antioxidant activity, a typical property of flavones. Taken together, our results demonstrate that synthetic biology represents a practical method for engineering plants to produce substantial amounts of flavonoids and flavonoid derivatives without the need for exogenous substrates.

A history-dependent integrase recorder of plant gene expression with single-cell resolution

During development, most cells experience a progressive restriction of fate that ultimately results in a fully differentiated mature state. Understanding more about the gene expression patterns that underlie developmental programs can inform engineering efforts for new or optimized forms. Here, we present a four-state integrase-based recorder of gene expression history and demonstrate its use in tracking gene expression events in Arabidopsis thaliana in two developmental contexts: lateral root initiation and stomatal differentiation. The recorder uses two serine integrases to mediate sequential DNA recombination events, resulting in step-wise, history-dependent switching between expression of fluorescent reporters. By using promoters that express at different times along each of the two differentiation pathways to drive integrase expression, we tie fluorescent status to an ordered progression of gene expression along the developmental trajectory. In one snapshot of a mature tissue, our recorder is able to reveal past gene expression with single cell resolution. In this way, we are able to capture heterogeneity in stomatal development, confirming the existence of two alternate paths of differentiation.

Engineering Nicotiana benthamiana as a platform for natural product biosynthesis

Nicotiana benthamiana is a model plant, widely used for research. The susceptibility of young plants to Agrobacterium tumefaciens has been utilised for transient gene expression, enabling the production of recombinant proteins at laboratory and commercial scales. More recently, this technique has been used for the rapid prototyping of synthetic genetic circuits and for the elucidation and reconstruction of metabolic pathways. In the last few years, many complex metabolic pathways have been successfully reconstructed in this species. In addition, the availability of improved genomic resources and efficient gene editing tools have enabled the application of sophisticated metabolic engineering approaches to increase the purity and yield of target compounds. In this review, we discuss recent advances in the use of N. benthamiana for understanding and engineering plant metabolism, as well as efforts to improve the utility of this species as a production chassis for natural products.

Biocomputing in plants, from proof of concept to application

In response to the challenges of climate change and the transition toward sustainability, synthetic biology offers innovative solutions. Most current plant synthetic biology applications rely on the constitutive expression of enzymes and regulators. To engineer plant phenotypes tuneable to environmental conditions and plant cellular states, the integration of multiple signals in synthetic circuits is required. While most circuits are developed in model organisms, numerous tools were recently developed to implement biocomputation in plant synthetic circuits. I presented in this review the tools and design methods for logic circuit implementation in plants. I highlighted recent and potential applications of those circuits to understand and engineer plant interaction with the environment, development, and metabolic pathways.

Synthetic developmental biology: molecular tools to re-design plant shoots and roots

Plant morphology and anatomy strongly influence agricultural yield. Crop domestication has strived for desirable growth and developmental traits, such as larger and more fruits and semi-dwarf architecture. Genetic engineering has accelerated rational, purpose-driven engineering of plant development, but it can be unpredictable. Developmental pathways are complex and riddled with environmental and hormonal inputs, as well as feedback and feedforward interactions, which occur at specific times and places in a growing multicellular organism. Rational modification of plant development would probably benefit from precision engineering based on synthetic biology approaches. This review outlines recently developed synthetic biology technologies for plant systems and highlights their potential for engineering plant growth and development. Streamlined and high-capacity genetic construction methods (Golden Gate DNA Assembly frameworks and toolkits) allow fast and variation-series cloning of multigene transgene constructs. This, together with a suite of gene regulation tools (e.g. cell type-specific promoters, logic gates, and multiplex regulation systems), is starting to enable developmental pathway engineering with predictable outcomes in model plant and crop species.