A Ratiometric Dual Color Luciferase Reporter for Fast Characterization of Transcriptional Regulatory Elements in Plants

Quantitative measures of clock protein dynamics in the mouse suprachiasmatic nucleus extends the circadian time-keeping model

The suprachiasmatic nucleus (SCN) synchronises circadian rhythmicity (~24 h) across the body. The SCN cell-autonomous clock is modelled qualitatively as a transcriptional-translational feedback loop (TTFL), with heteromeric complexes of transcriptional activator and repressor proteins driving cyclical gene expression. How these proteins really behave within the SCN, individually and in relation to each other, is poorly understood. Imaging SCN slices from a novel array of knock-in reporter mice, we quantify the dynamic behaviours of combined repressors PERIOD2 (PER2) and CRYPTOCHROME1 (CRY1), and activator BMAL1. We reveal a spectrum of protein-specific intracellular and spatiotemporal behaviours that run counter to the qualitative TTFL model. We also show that PER and CRY1 exert independent actions on TTFL oscillations, and that their individual stabilities play a critical role in SCN circadian dynamics. These results reveal a rich and unanticipated complexity in the dynamic behaviours and functions of endogenous circadian proteins, prompting re-appraisal of current transcriptional-translational feedback loop models of the suprachiasmatic nucleus.

Best Practices and Pitfalls in Developing Nanomaterial Delivery Tools for Plants

Numerous reports of nanomaterial-assisted delivery of DNA, RNA, and protein to plants for biotechnology applications emerged over the past decade. While the field has experienced rapid growth, best practices for developing and validating nanomaterial delivery tools for plants have not yet been established. Best practices are well-established for clinical/animal cell delivery experiments, yet plants pose a distinct challenge requiring separate considerations due to their unique tissue structures and cellular morphology. In this Perspective, we provide recommendations and highlight pitfalls in developing nanomaterial tools for delivery of "Central Dogma" cargos to plants. Given the ongoing interest in the field, this discussion will aid in improving the rigor of this nascent field toward practical applications of nanomaterial delivery tools.

A Wheat Protoplast Assay for Positive Effector Screening and Investigation of Host-Pathogen Interactions

Fungal pathogens present a severe risk to food systems; however, complex crop-microbe interactions are challenging to study using tools developed for model species. In particular, efficient screening and rapid assessment of microbial effectors is hindered by a lack of cloned resistance (R) genes and difficulty in validating large numbers of predicted effector candidates. This chapter describes a protocol for preparing wheat protoplasts to enable positive identification of host defense induction without overexpression of a cloned R gene, increasing the available pool of host resistance genes for screening. The assay uses polyethylene glycol (PEG)-calcium-mediated transient transfection to introduce candidate effector gene constructs into wheat protoplasts, with a defense-activated reporter for inducing a positive readout with internal normalization, indicating host recognition. This protocol provides a valuable tool for the study of host-pathogen interactions in wheat, contributing to improved resources for the development of disease-resistant crops and genome-informed pathogen surveillance.

Multiplexed effector screening for recognition by endogenous resistance genes using positive defense reporters in wheat protoplasts

Plant resistance (R) and pathogen avirulence (Avr) gene interactions play a vital role in pathogen resistance. Efficient molecular screening tools for crops lack far behind their model organism counterparts, yet they are essential to rapidly identify agriculturally important molecular interactions that trigger host resistance. Here, we have developed a novel wheat protoplast assay that enables efficient screening of Avr/R interactions at scale. Our assay allows access to the extensive gene pool of phenotypically described R genes because it does not require the overexpression of cloned R genes. It is suitable for multiplexed Avr screening, with interactions tested in pools of up to 50 Avr candidates. We identified Avr/R-induced defense genes to create a promoter-luciferase reporter. Then, we combined this with a dual-color ratiometric reporter system that normalizes read-outs accounting for experimental variability and Avr/R-induced cell death. Moreover, we introduced a self-replicative plasmid reducing the amount of plasmid used in the assay. Our assay increases the throughput of Avr candidate screening, accelerating the study of cellular defense signaling and resistance gene identification in wheat. We anticipate that our assay will significantly accelerate Avr identification for many wheat pathogens, leading to improved genome-guided pathogen surveillance and breeding of disease-resistant crops.

A gene regulatory network critical for axillary bud dormancy directly controlled by Arabidopsis BRANCHED1

The Arabidopsis thaliana transcription factor BRANCHED1 (BRC1) plays a pivotal role in the control of shoot branching as it integrates environmental and endogenous signals that influence axillary bud growth. Despite its remarkable activity as a growth inhibitor, the mechanisms by which BRC1 promotes bud dormancy are largely unknown. We determined the genome-wide BRC1 binding sites in vivo and combined these with transcriptomic data and gene co-expression analyses to identify bona fide BRC1 direct targets. Next, we integrated multi-omics data to infer the BRC1 gene regulatory network (GRN) and used graph theory techniques to find network motifs that control the GRN dynamics. We generated an open online tool to interrogate this network. A group of BRC1 target genes encoding transcription factors (BTFs) orchestrate this intricate transcriptional network enriched in abscisic acid-related components. Promoter::β-GLUCURONIDASE transgenic lines confirmed that BTFs are expressed in axillary buds. Transient co-expression assays and studies in planta using mutant lines validated the role of BTFs in modulating the GRN and promoting bud dormancy. This knowledge provides access to the developmental mechanisms that regulate shoot branching and helps identify candidate genes to use as tools to adapt plant architecture and crop production to ever-changing environmental conditions.

Benchmarking Intrinsic Promoters and Terminators for Plant Synthetic Biology Research

The emerging plant synthetic metabolic engineering has been exhibiting great promise to produce either value-added metabolites or therapeutic proteins. However, promoters for plant pathway engineering are generally selected empirically. The quantitative characterization of plant-based promoters is essential for optimal control of gene expression in plant chassis. Here, we used N. benthamiana leaves and BY2 suspension cells to quantitatively characterize a library of plant promoters by transient expression of firefly/Renilla luciferase. We validated the dual-luciferase reporter system by examining the correlation between reporter protein and mRNA levels. In addition, we investigated the effects of terminator-promoter combinations on gene expression and found that the combinations of promoters and terminators resulted in a 326-fold difference between the strongest and weakest performance, as reflected in reporter gene expression. As a proof of concept, we used the quantitatively characterized promoters to engineer the betalain pathway in N. benthamiana. Seven selected plant promoters with different expression strengths were used orthogonally to express CYP76AD1 and DODA, resulting in a final betalain production range of 6.0-362.4 μg/g fresh weight. Our systematic approach not only demonstrates the various intensities of multiple promoter sequences in N. benthamiana and BY2 cells but also adds to the toolbox of plant promoters for plant engineering.

Toolboxes for plant systems biology research

The terms 'systems' and 'synthetic biology' are often used together, with most scientists striding between the two fields rather than adhering to a single side. Often too, scientists want to understand a system to inform the design of gene circuits that could endow it with new functions. However, this does not need to be the progression of research, as synthetic constructs can help improve our understanding of a system. Here, we review synthetic biology tool kits with the potential to overcome pleiotropic effects, compensatory mechanisms, and redundancy in plants. Combined with -omics techniques, these tools could reveal novel insights on plant growth and development, an aim that has gained renewed urgency given the impact of climate change on crop productivity.