CARBON Newsletter (5 April) - Your Latest News About CRISPR in AgroBio

Top picks

• Researchers in China have used CRISPR-Cas9 in goats to knockout stearoyl-CoA desaturase 1 (SCD1), the key enzyme catalyzing monounsaturated fatty acid synthesis in milk lipid metabolism. In SCD1-knockout goats, milk fat percentage and unsaturated fatty acid levels were reduced but other milk components were unchanged, and there was no effect on goat growth or serum biochemistry.
• A study in the journal Science suggests that CRISPR knockout of one gene, KRN2, in maize and rice can increase yield up to 10% with no apparent trade-offs in other agronomic traits. The gene is one of 490 pairs of genes that the Chinese researchers found to serve analogous functions in both grains. Though the two crops have very different domestication histories with different centres of origin and different habitats, these conserved genes are thought to be driven at least in part by convergent selection.

Technical advances

• American researchers have developed synthetic promoter elements in which regions upstream of the minimal 35S CaMV promoter are designed from scratch to interact via programmed gRNAs with dCas9 fusions that allow activation of gene expression. The ability to form complex circuitry was demonstrated via the ethylene-driven, ratiometric expression of fluorescent proteins in single plants.
• A method to reduce off-target mutations in the CRISPR-Cas9 system in plants is presented by Chinese scientists. The method employs the temperature-independent mesoporous silica nanoparticles (MSNs)-gene delivery system to target plants at 37 °C. At this temperture, on-target mutagenesis of SpCas9 is increased leading to fewer off-target effects.
• Chinese researchers have improved the editing efficiency of CRISPR-LbCas12a in Arabidopsis by optimizing the crRNA expression strategies and Pol II promoters. The authors find that the combination of tRNA-crRNA fusion strategy and RPS5A promoter in the CRISPR-LbCas12a system has highest editing efficiency, while CRISPR-LbCas12a driven by EC1f-in(crR)p had the highest ratio of homozygous and bi-allelic mutants.

Disease control

• American researchers describe a CRISPR based assay for the detection of cell wall-less phytopathogenic bacterium ‘Candidatus Phytoplasma trifolii’ that causes potato purple top (PPT) and potato witches’ broom (PWB). The DNA endonuclease targeted CRISPR trans reporter (DETECTR) assay couples isothermal amplification and Cas12a trans-cleavage of fluorescent oligonucleotide reporter and can detect attomolar levels of the 16S–23S ribosomal DNA (rDNA) intergenic transcribed spacer (ITS) sequences.

Nutritional quality

• A Chinese research group has used CRISPR-Cas9 mediated knockout of the regulatory microRNA (miRNA)-130b for improving the beneficial fatty acids content in goat milk. The authors deleted 43 nucleotides by targeting the genomic sequence of pre-miR-130b with two gRNAs, and that resulted in increased expression of target genes PGC1α and PPARG. This, in turn, resulted in the decreased proportion of several monounsaturated fatty acids and polyunsaturated fatty acids.

Industry

• The leading gene editing food company Pairwise is ready to market CRISPR-engineered mustard greens (Brassica juncea) without the usual strong bitter taste and pungent smell. The product got USDA approval in 2020 and will be launched next year in the form of packaged salads as the first product in the series Conscious Foods.

Regulation and opinion

• The Union Ministry of Environment and Forest in India will allow genome-edited plants, or organisms without any “foreign” genes to be subjected to a different regulatory process than the one applied to genetically engineered product. The change involves gene edited plants belonging to the categories SDN1 and SDN2 that largely involve “knocking off” or “overexpressing” certain traits.
• An opinion piece in Vox discusses the fight over gene-edited meat that was recently spurred by the FDA approval of CRISPR edited cattle that had gained heat resistance. The author weighs the cons of a future of factory farming on overdrive almost certainly to the detriment of animal welfare against the pros of using the genetic tools to alleviate some animal suffering.

Reviews

• A review by Canadian researchers disucuss the impact of gene-editing strategies and the available in vitro and in vivo models of chronic wasting disease (CWD) in deer, elk and other cervids. CWD is a contagious prion disease and CRISPR-Cas9 was recently used for replacing the PrP gene in mouse and cell cultures for developing CWD models.
• Recent advances in plant gene silencing methods are discussed in a review by Indian scientists. The review discusses gene-editing systems like CRISPR-Cas and microRNA-based technologies like microRNA-induced gene silencing (MIGS) and microRNA-mediated virus-induced gene silencing (MIR-VIGS).
• Researchers in Kenya review the recent advancements and perspectives on the application of CRISPR-Cas9 gene editing for the control of bacterial wilt diseases in banana, that are caused by caused by Xanthomonas campestris pv. Musacearum and other pathogens. Different methods for creating disease resistance are discussed, including knocking out the disease-causing susceptibility (S) genes or activating the expression of the plant defense genes.
• A review by scientists in Malaysia looks at the applications and challenges of CRISPR-Cas9 in plant biotechnology. The recent progress in utilising gene editing to enhance certain traits in beneficial crops is discussed, and the authors emphasise the need to improve current delivery methods or develop new ones.
• Researchers in India briefly review different genome editing technologies deployed for crop improvement, and the fundamental differences between gene editing and transgene-based approach. The review also summarise the recent advances in genome editing and how this radical expansion can complement the previously established technologies along with breeding for creating designer crops.
• A Chinese review discuss the application status of emerging precise genome editing technology in plants with a special emphasis on the potential limitations and technical bottlenecks in rapeseed gene editing. The review summarizes current reports about the application of the CRISPR-Cas9 system for gene function research and genetic improvement in rapeseed, involving important agronomic traits such as yield, oil content, and fatty acid composition.

Meetings, webinars etc.

• The 9th Plant Genomics and Gene Editing Congress: Europe will take place 11-12 April in The Hague, Netherlands. The 2022 conference will examine the latest in genomics and gene editing methods for specific crop plants and horticulture as well as the latest applications of artificial intelligence and machine learning in plant science.