Chinese scientists find natural selection loophole that could help transform food security

By Victoria Bela

Scientists in China have found a way to bypass natural plant gene inheritance, by using a CRISPR-based gene editing system to boost the transmission of preferred genes even when they are detrimental to a plant.

By harnessing a system that uses both a toxin and an antidote to target the male plant germline, the scientists were able to overcome the natural Mendelian transmission rate, achieving gene transmission rates of up to 99 per cent over two generations.

″Facing diverse challenges such as threats to food security from agricultural weeds and the environmental crisis of invasive plants, the genetic manipulation of wild plant populations has emerged as a potentially powerful and transformative strategy,″ the team wrote in a paper published in the peer-reviewed journal Nature Plants on Monday.

Efforts to breed for ideal genes that can be detrimental to their plants have been limited by the classical principles of Mendelian inheritance and Darwinian natural selection, the team from the Chinese Academy of Sciences and Peking University said in their paper.

Mendelian inheritance is a principle that describes how genetic traits are passed from one generation to another, and states that the two alleles contained within a single gene each have a 50 per cent chance of passing on to offspring through reproduction.

″Synthetic gene drives, inspired by natural selfish genetic elements and transmitted to progeny at super-Mendelian (greater than 50 per cent) frequencies, present transformative potential for disseminating traits that benefit humans throughout wild populations, even facing potential fitness costs,″ the team said.

A gene drive is a genetic engineering technique that allows genes to be modified in a way that discourages them from following the usual rules of heredity, thereby increasing the likelihood that a particular suite of genes will be passed onto the next generation and spread through a population.

″We constructed a gene drive system in plants called CRISPR-Assisted Inheritance utilising NPG1 (CAIN), which uses a toxin-antidote mechanism in the male germline to override Mendelian inheritance,″ the researchers said.

The synthetic ″toxin″ – in this case, a guide RNA Cas9 cassette – was used to disrupt the No Pollen Germination 1 (NPG1) gene limiting pollen germination. A CRISPR-resistant ″antidote″ copy of NPG1 is then used to rescue pollen cells that carry the desired gene drive.

A red fluorescent seed marker was added to CAIN to track the progress of the gene drive.

″CAIN transmission rates greatly exceeded the expected Mendelian inheritance of 50 per cent in heterozygous male parents, reaching 88 to 99 per cent within two successive generations,″ the team wrote.

″We established CAIN as a state-of-the-art tool to efficiently modify entire plant populations.″

The researchers chose thale cress, a self-pollinating plant from the mustard family, as the model to limit the chances of inadvertently releasing CAIN into wild populations.

CAIN has advantages over other gene drive systems, which can develop a higher amount of resistance alleles that limit their efficacy. Compared to other systems, the team said they also chose to target the male germline over the female germline, since toxin-antidote gene drives targeting the female germline can compromise fertility and limit efficiency.

CAIN could be used in a variety of plants, as NPG1 is conserved across many species. One potential use of the system would be to target herbicide resistant genes in weeds to help reduce the need for excessive herbicide spraying, according to the researchers.

″This gene drive-based approach thus seeks to balance crop protection and environmental considerations to minimise the loss of biodiversity while optimising productivity,″ the researchers wrote.

The team acknowledged that even if gene drive technologies are biosafe and self-containment strategies are implemented, the strategies ″may not be feasible in cases of intentional misuse of gene drive technology, targeting domestic crops or wild plants″.

One method to safeguard against misuse ″could be the intentional creation and if necessary, release of suppressor lines. Editing the native NPG1 allele to resist Cas9 cleavage is a particularly straightforward and efficient method″, the team said.

″As we venture into this new frontier in genetic engineering, [CAIN] and other gene drive systems could reshape ecological management and agricultural practices.″