Environmentally friendly CRISPR technology can control crop pests

Ensuring that we and future generations have enough to eat in the face of climate change and the resulting migration of species involves the necessary evil of killing the insects that destroy our crops. Conventional, environmentally harmful chemical pesticides are species-agnostic and often kill harmful insects and gradually decline in effectiveness as pests develop resistance. Technologies that selectively control or kill pest species offer a safer option.

One such invasive pest is the pest Drosophila suzuki, which poses a threat to agricultural yields, especially in the production of fruits such as berries, cherries, plums and grapes in Western countries. Thus the effect of control measures to limit the spread D. Suzuki has been less than optimal.

An article published in GEN Biotechnology (“Precision Guided Sterile Males Suppress Populations of an Invasive Crop Pest”) reports the development of a programmable CRISPR-based method that, if deployed at scale in the wild, could potentially replace fertile males. D. Suzuki with sterile counterparts, thereby effectively, specifically, and safely suppressing this pest population. Although developed in D. Suzuki, The authors claim that this method can be modified to target other insect species, obviating the need for environmentally unfriendly pesticides.

Omar Akbari, PhD, a professor in the School of Biological Sciences in the Department of Cell and Developmental Biology at the University of California, San Diego, is the study’s corresponding author.

The study, conducted by scientists at the University of California, San Diego (UCSD), uses co-lead authors Nicolae Kandul, PhD, Junru Liu, PhD, and Anna Buchman, PhD, and corresponding author, Omar Akbari, PhD. A temperature-inducible, precisely directed, sterile insect technique (pgSIT), reported by the team in an earlier study, to produce sterile, but fit and competitive D. Suzuki Men with slightly shorter lifespans. Through experimental experiments and mathematical modeling, researchers have shown that repeated releases can quickly and successfully prevent or eliminate male infertility. D. Suzuki Population. (Akbari’s team has used pgSIT to sterilize mosquitoes in previous studies).

“This is a safe, evolutionarily stable system,” said Akbari, a professor in the School of Biological Sciences’ Department of Cell and Developmental Biology at UCSD. “The system does not lead to uncontrolled spread nor does it persist in the environment – both important safety features that help it gain approval for use.”

“This extends previously published work,” said Rodolphe Barangau, PhD, editor CRISPR Journal. “The study illustrates how next-generation CRISPR-based gene drives can be used to control crop pests. Data convincingly demonstrate that this approach has technical advantages and enables population suppression through the deployment of competitive sterile males. Importantly, this proof-of-concept study Provides a basis for considering commercial applications.”

The pgSIT system edits essential genes that determine sex and fertility. The authors used two transgenics D. Suzuki strains, one expressing Cas9 in germline and somatic cells and the other expressing guide RNA targeting genes essential for female survival and male fertility, such as sex lethal (Sxl), double sex (dsx), and transformer (tra). This technique produced 100% sterile males with females killed or transformed into intersex flies.

The authors showed that the pgSIT system was effective when pgSIT was released to sterile males at a ratio that was comparable to approaches using conditional female lethality strains, and lower than the release ratio recommended for conventional SIT (sterile insect technique) paradigms. In addition, traditional SIT programs use DNA-damaging agents, such as ionizing radiation, to generate sterile males. This limits the fitness and mating competition of free males.

survival curve
Survival curves show a shorter lifespan of pgSIT D. suzuki males compared to wild-type males. [adapted from Kandul NP, et al, GEN Biotechnology, 2022]

The authors showed that the combination of pgSIT D. Suzuki Wild-type males have significantly reduced egg hatching rates, suggesting that sterile males are competitive and successfully compete with wild-type males to mate with females. The authors also showed that increasing the release ratio of pgSIT males to wildtype males increased the rate of population decline.

“pgSIT is an attractive way to control technology D. Suzuki population,” said Qutbuddin Mollah, Ph.D., a scientist at the National Rice Research Institute in Cuttack, India. Plant cells journal. “However, before environmental release, we must be careful to avoid any expected risks and unintended ecological consequences. If we can develop a gene drive recall system, we will have more confidence in the environmental release of gene-drive insects.”

Barrangou agreed. “We must be aware and cautious about practical deployments and ensure that proper studies are carried out to assess release safety and ecological impacts and consequences,” he said. “Depending on the release scale and pattern, population reduction and control rather than eradication per se is likely to result.”

Akbari said his team has developed pgSIT for several species over the past four years, and hopes to use it as a platform technology to safely control the spread of other pests in the real world.

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