Synthetic promoters from blueberry red ringspot virus (BRRV)

Designing artificial synthetic promoters for accurate, smart, and versatile gene expression in plants

With the development of high-throughput biology techniques and artificial intelligence, it has become increasingly feasible to design and construct artificial biological parts, modules, circuits, and even whole systems. To overcome the limitations of native promoters in controlling gene expression, artificial promoter design aims to synthesize short, inducible, and conditionally controlled promoters to coordinate the expression of multiple genes in diverse plant metabolic and signaling pathways. Synthetic promoters are versatile and can drive gene expression accurately with smart responses; they show potential for enhancing desirable traits in crops, thereby improving crop yield, nutritional quality, and food security. This review first illustrates the importance of synthetic promoters, then introduces promoter architecture and thoroughly summarizes advances in synthetic promoter construction. Restrictions to the development of synthetic promoters and future applications of such promoters in synthetic plant biology and crop improvement are also discussed.

Synthetic sub-genomic transcript promoter from Horseradish Latent Virus (HRLV)

We characterized an efficient chimeric sub-genomic transcript promoter from Horseradish Latent Virus, FHS4, active in both dicot and monocot plants, and it could be a potential tool for plant biotechnology. Plant pararetroviruses are a rich source of novel plant promoters widely used for biotechnological applications. Here, we comprehensively characterized a unique sub-genomic transcript (Sgt) promoter of Horseradish Latent Virus (HRLV) and identified a fragment (HS4; - 340 to + 10; 351 bp) that showed the highest expression of reporter genes in both transient and transgenic assays as evidenced by biochemical, histochemical GUS reporter assay and transcript analysis of uidA gene by qRT-PCR. Phylogenetic analysis showed that the HSgt promoter was closely related to the sub-genomic promoter of the Cauliflower Mosaic Virus (CaMV19S). We found that the as-1 element and W-box played an important role in the transcriptional activity of the HS4 promoter. Furthermore, the HS4 promoter was also induced by salicylic acid. Alongside, we enhanced the activity of the HS4 promoter by coupling the enhancer region from Figwort Mosaic Virus (FMV) promoter to the upstream region of it. This hybrid promoter FHS4 was around 1.1 times stronger than the most commonly used promoter, 35S (Cauliflower Mosaic Virus full-length transcript promoter), and was efficient in driving reporter genes in both dicot and monocot plants. Subsequently, transgenic tobacco plants expressing an anti-microbial peptide BrLTP2.1 (Brassica rapa lipid transport protein 2.1), under the control of the FHS4 promoter, were developed. The in vitro anti-fungal assay revealed that the plant-derived BrLTP2.1 protein driven by an FHS4 promoter manifested increased resistance against an important plant fungal pathogen, Alternaria alternata. Finally, we concluded that the FHS4 promoter can be used as an alternative to the 35S promoter and has a high potential to become an efficient tool in plant biotechnology.

Further Characterization of MUAS35SCP and FUAS35SCP Recombinant Promoters and Their Implication in Translational Research

Recombinant promoters are of high value in translational research. Earlier, we developed two recombinant promoters, namely MUAS35SCP and FUAS35SCP, and their transcriptional activities were found to be stronger than that of the most widely used CaMV35S promoter in dicot plants. Presently, we are reporting constitutive expression of both GUS and GFP reporters under the control of these promoters in several monocots, including rice, wheat, and pearl millet. We observed that these promoters could express the reporter genes constitutively, and their expression abilities were almost equal to that of the CaMV35S² promoter. Plant-derived enriched PaDef (Persea americana var. drymifolia defensin) and NsDef2 (Nigella sativa L. defensin 2) antimicrobial peptides expressed under the control of these promoters arrest the growth of devastating phytopathogens like Pseudomonas syringae, Rhodococcus fascians, and Alternaria alternata. We observed that plant-derived NsDef2 and PaDef under control of these promoters showed approximately 80-90% inhibitory activity against Pseudomonas syringae. Hence, these promoters were constitutive and universal, as they can drive the expression of transgenes in both dicot and monocot plants. Alongside, these promoters could become a valuable tool for raising genetically modified plants with in-built resistance toward phytopathogens.