On the cover

Genome-editing technology is a biological mutation induction technique that is attracting attention as a novel and effective tool for mutation breeding. CRISPR/Cas9 technology is now used to develop genome-editing crops. This photograph was taken in August 2022 of the harvesting of Europe’s first field trial of genome-edited (CRISPR) wheat. This special issue in Breeding Science contains six review articles and one research paper, which focus on recent advances in the introduction of global trends in the regulation rules for genome-edited crops (foods), trends in the social license for genome-edited crops in Japan, the development of new genome-editing technologies, and genome-edited crops that are expected to be implemented in society in the future: wheat, melon, and tomato (This issue, p. 37–46).

(H. Ezura: The University of Tsukuba)

There is a need to introduce new regulations regarding genome editing technology and its application to agriculture and food. Regulations are different among countries and sometimes inconsistent. Here, we summarize the current regulations regarding the use of genome editing technology in agriculture and food in various countries around the world. We also discuss the main regulatory developments expected to occur in the future.

The success or failure of food technologies in society depends to a large extent on the public interest, concerns, images, and expectations surrounding them. This paper delves into the landscape of public attitudes towards gene-edited foods in Japan, exploring the reasons behind the acceptance or rejection of these products. A literature review and preliminary findings from a survey conducted in Japan in 2022, aim to identify key issues crucial for evaluating societal acceptance of gene-edited foods. The study showed that the public view gene-edited foods as somewhat unnatural, but upon closer examination, significant variation in attitudes was observed among respondents. Some respondents expressed a favorable perception towards gene-edited foods, particularly those that benefit consumers, while others expressed concerns about its perceived artificiality. Moreover, a significant number of respondents displayed indifference or lack of clear perspective regarding gene-edited foods. These findings reflect the complex relationship between public attitudes, naturalness, and social acceptance of gene-edited foods. Furthermore, the study indicates the importance of paying close attention to those who refrain from expressing their viewpoints in the survey. This nuanced landscape warrants further exploration.

Food shortages due to population growth and climate change are expected to occur in the near future as a problem that urgently requires solutions. Conventional breeding techniques, notably crossbreeding and mutation breeding, are known for being inefficient and time-consuming in obtaining seeds and seedlings with desired traits. Thus, there is an urgent need for novel methods for efficient plant breeding. Breeding by genome editing is receiving substantial attention because it can efficiently modify the target gene to obtain desired traits compared with conventional methods. Among the programmable sequence-specific nucleases that have been developed for genome editing, CRISPR–Cas12a and CRISPR–MAD7 nucleases are becoming more broadly adopted for the application of genome editing in grains, vegetables and fruits. Additionally, ST8, an improved variant of MAD7, has been developed to enhance genome editing efficiency and has potential for application to breeding of crops.

The advent of CRISPR/Cas9 has had a disruptive impact on the world by bringing about dramatic progress and rapid penetration of genome editing technology. However, even though gene disruption can be easily achieved, there has been a challenge in freely changing the sequence. To solve this problem, various novel technologies have emerged in recent years to realize free rewriting of genome sequences. In this review, scarless editing by two-step HDR, a technology that can freely rewrite genomes from a single nucleotide to more than several thousand nucleotides, will be introduced.

We review the undertaking of a field trial of low asparagine wheat lines in which the asparagine synthetase gene, TaASN2, has been knocked out using CRISPR/Cas9. The field trial was undertaken in 2021–2022 and represented the first field release of genome edited wheat in Europe. The year of the field trial and the period since have seen rapid changes in the regulations covering both the field release and commercialisation of genome edited crops in the UK. These historic developments are reviewed in detail. Free asparagine is the precursor for acrylamide formation during high-temperature cooking and processing of grains, tubers, storage roots, beans and other crop products. Consequently, work on reducing the free asparagine concentration of wheat and other cereal grains, as well as the tubers, beans and storage roots of other crops, is driven by the need for food businesses to comply with current and potential future regulations on acrylamide content of foods. The topic illustrates how strategic and applied crop research is driven by regulations and also needs a supportive regulatory environment in which to thrive.

Genome editing technologies are promising for conventional mutagenesis breeding, which takes a long time to remove unnecessary mutations through backcrossing and create new lines because they directly modify the target genes of elite strains. In particular, this technology has advantages for traits caused by the loss of function. Many efforts have been made to utilize this technique to introduce valuable features into crops, including maize, soybeans, and tomatoes. Several genome-edited crops have already been commercialized in the US and Japan. Melons are an important vegetable crop worldwide, produced and used in various areas. Therefore, many breeding efforts have been made to improve its fruit quality, resistance to plant diseases, and stress tolerance. Quantitative trait loci (QTL) analysis was performed, and various genes related to important traits were identified. Recently, several studies have shown that the CRISPR/Cas9 system can be applied to melons, resulting in its possible utilization as a breeding technique. Focusing on two productivity-related traits, disease resistance, and fruit quality, this review introduces the progress in genetics, examples of melon breeding through genome editing, improvements required for breeding applications, and the possibilities of genome editing in melon breeding.

Plant factories with artificial light are less affected than open-air areas to environmental factors in crop cultivation and are attracting attention as one of the solutions to the world’s food problems. However, the cost of cultivation in plant factories is higher than open-air cultivation, and currently, profitable factory-grown crop varieties are limited to those that are small or have a short growing period. Tomatoes are one of the main crops consumed around the world, but due to their large plant height and width, they are not yet suitable for mass production in plant factories. In this study, the DWARF (D) and SELF-PRUNING (SP) genes of the GABA hyperaccumulating tomato variety #87-17 were genome-edited by the CRISPR–Cas9 method to produce dwarf tomato plants. The desired traits were obtained in the T₁ genome-edited generation, and the fruit traits were almost the same as those of the original variety. On the other hand, the F₂ cross between #87-17 and Micro-Tom containing the d and sp mutations was dwarfed, but the fruit phenotype was a mixture of the traits of the two varieties. This indicates that genome editing of these two genes using CRISPR–Cas9 can efficiently impart traits suitable for plant factory cultivation while retaining the useful traits of the original cultivar.