CARBON Newsletter (8 March 2022) - Your Latest News About CRISPR in AgroBio

Top picks

• Chinese researchers have used CRISPR-Cas9 to disrupt natural miRNA-mediated inhibition of the growth-regulating gene GS2 and thereby obtain rice with increased grain size and yield. Gene-editing resulted in a mutant named GS2^E carrying an in-frame 6-bp deletion and 1-bp substitution within the miR396-targeted sequence. As a result, thousand grain weight and grain yield per plant of GS2^E plants were increased by 23.5% and 10.4%, respectively.
• When working with plants, researchers tend to pay less attention to off-target editing and other unintended gene-editing events when working with plants than in human biomedical research. An extensive literature review by Dutch researchers gathers information on the occurrence and nature of CRISPR-Cas off-target edits in plants. It is shown that off-target edits are predominantly detected via biased analysis of predicted off-target sites instead of unbiased genome-wide analysis. Furthermore, the review finds that CRISPR-Cas-edited plants showed lower off-target mutation frequencies than conventionally bred plants. This can aid discussions on the relevance of evaluating off-target modifications for risk assessment of CRISPR-Cas-edited plants.

Technical advances

• Chinese researchers present a method for rapidly identifying and visual tracking of sequences derived from crop wild relatives (CWRs) that can be used for CRISPR-Cas9-mediated crop pre-breeding to address climate change and food demand challenges. Using cultivated cucumber (C. sativus, CC, 2n = 2x = 14) and Cucumis hystrix (HH, 2n = 2x = 24), a wild species carrying many favourable traits, the authors use synthetic double-stranded oligo probes to paint and visualise chromosome architectures and variation in allopolyploids.
• The bacterium Ochrobactrum haywardense, which was recently discovered to be capable of efficient plant transformation, has been used for the targeted and marker-free delivery of CRISPR-Cas9 components and donor templates in soybean. The approach generated up to 3.4% targeted insertion of the donor sequence into the target locus in T0 plants, with ∼ 90% mutation rate observed at the genomic target site.

Disease control

• Resistance to bacterial blight has been obtained in cassava through CRISPR-Cas9-targeted editing of the MeSWEET10a promoter. MeSWEET10a is a disease-susceptibility gene of the pathogen Xanthomonas axonopodis pv. manihotis, and its knockout resulted in all mutated cassava lines having the same morphological and yield-related traits as the wild type.

Agronomic traits

• Researchers in China have developed a predictable and effective approach to creating herbicide-resistant germplasm by gene editing the acetohydroxyacid synthase (AHAS) gene. The authors designed mutations using a mutation-dependent biomacromolecular quantitative structure-activity relationship (MB-QSAR) strategy and used CRISPR-Cas9 to introduce them into Arabidopsis. As a result, gene-edited plants exhibited high resistance to multiple acetohydroxyacid synthase-inhibiting herbicides, including chlorsulfuron, bispyribac-sodium, and flucarbazone-sodium.
• Chinese researchers have used CRISPR-Cas9 to create mutants in the cytokinin oxidase/dehydrogenases (CKXs) genes that play a role in plant growth and development. Two double mutants, osckx1 osckx2 and osckx4 osckx9, displayed contrasting phenotypic changes in tiller number and panicle size compared to the wild type. The research can ultimately be used to improve rice yield.
• Canadian researchers have used CRISPR-Cas9 to generate drought resistance in Arabidopsis by knocking out the gene CBF4. ABA and osmotic stress induce CBF4, which negatively regulates ABA responses while promoting stomatal development and reducing drought tolerance.

Regulation & Opinion

• FDA has cleared the regulatory path for gene-edited cattle in the US. The cattle by Recombinetics are CRISPR gene-edited in the prolactin receptor (PRLR) gene to make a truncated PRLR protein known from conventional breeding as the SLICK phenotype. These animals have short, slick coats that let them more easily withstand hot weather. This reduces heat stress and allows for more efficient meat production.
• In a piece in New Food Magazine, food chemist Patrick McNamara shares his thoughts on the pros and cons of gene-edited foods. The article evaluates the different arguments of proponents and opposers and also gives an overview of the current legislation in the EU and globally.
• A News & Views piece in Nature Plants discusses the recent use of CRISPR-Cas9 to generate powdery mildew-resistant wheat without any growth penalty. One month ago, CARBON interviewed the senior author of the original study, Caixia Gao, who explained the route and the perspectives of the breakthrough achievement.
• A survey of Vietnamese consumers' attitudes towards genome-edited (GE) and genetically modified (GM) foods has been conducted by researchers in Japan. The survey shows a high correlation between attitudes toward GE and GM foods. Therefore, the authors suggest providing in-depth information to reduce this correlation and thereby increase consumers' acceptance of GE food.
• An editorial in Plant Physiology provides an update on gene editing and its applications for plant biology research, improvement of existing crops, and de novo domestication of new crops. The update summarises the technical achievements and the various gene-editing strategies and highlights specific studies that use CRISPR-mediated gene editing in crop improvements and de novo domestication.

Reviews

• CRISPR-Cas9 gene editing is highlighted as a simple and efficient approach for marker-free selection in rice in a review that looks into co-transformation, site-specific recombination and transposon-based strategies. The Indian authors summarise and analyse the recent advances that have enormous potential in rice improvement.
• The role of CRISPR-based genome alteration and nanotechnology in improving the agronomic performance through rhizosphere microbiomes is highlighted in another review by Indian researchers. The paper summarises the recent vital molecular processes that underlie the different beneficial plant-microbe interactions imperative for enhancing plant fitness and resilience under-challenged agriculture.
• French researchers review the latest biotechnology tools and targets for improving abiotic stress tolerance in protein legumes, including drought, high salinity, heat and cold, and heavy metal stress. The tools surveyed include transgenesis, CRISPR-Cas and RNA interference, and the review also discusses promising molecular targets, perspectives, and future perspectives for enhancing abiotic stress tolerance.
• Chinese researchers discuss the application of CRISPR-Cas gene editing in medicinal plants. The review creatively puts forward the development direction of CRISPR technology applied to medicinal plant gene editing. Furtheremore, it aims to provide a reference for using this technology in genome functional studies, synthetic biology, genetic improvement, and germplasm innovation of medicinal plants.
• A review by researchers from Pakistan discusses how scientists can use CRISPR-Cas gene editing for a paradigm shift towards sustainable agriculture and biotechnology. Among other topics, the review summarises the major role of CRISPR–Cas in plants in enhancing pesticide and disease resistance, quality, yield, breeding, and faster domestication.

Meetings

• The 9th Plant Genomics and Gene Editing Congress: Europe will be held in The Hague, Netherlands, 11-12 April 2022. The conference will examine the latest in genomics and gene editing methods for specific crop plants and horticulture and explore developments in genomics and gene editing for plant research in crop trait development, disease resistance, epigenetics and plant breeding. Featured speakers include Beat Keller, Alan Schulman, Jurriaan Ton and Sadiye Hayta.