Researchers have made a breakthrough in understanding how plants can prevent the transmission of viruses to their offspring, potentially leading to stronger and more disease-resistant crops. This discovery also has significant implications for reducing the spread of diseases from mothers to human children.
Given that plant viruses can easily spread across borders through the seed trade, addressing parent-to-progeny disease transmission is a critical global priority.
“Viruses can hide in seeds for years, making this one of the most important issues in agriculture,” said UC Riverside distinguished professor Shou-Wei Ding in the Department of Microbiology and Plant Pathology.
The ability of mother plants to prevent the spread of viruses to most of their offspring has puzzled scientists for a century. A team led by UCR has successfully identified the immune pathway that stops the virus from being transmitted from parent to progeny.
The research, detailed in a paper, used a strategy to pinpoint the pathway that prevents vertical transmission. By inoculating hundreds of Arabidopsis varieties with cucumber mosaic virus, the researchers identified genes that make the plants and their progeny more resistant to the virus, which can infect over 1,000 plant species and cause various symptoms.
These two crucial genes, active only during early seed development, play a pivotal role in the RNA interference pathway. Within cells, genetic information undergoes conversion from DNA to RNA and then to proteins.
This process involves the cutting of double-stranded RNA into small interfering RNA (siRNA) fragments, which are utilized to inhibit the production of certain proteins, particularly those stemming from foreign viruses.
“Many organisms produce siRNAs to control and inhibit viral infections,” Ding explained. “We believe the reason these plants can prevent seed infections is because the antiviral RNA interference pathway is active when seeds are being developed within mother plants.”
In order to test their hypothesis, the researchers created mutant plants by deleting two crucial RNA interference pathway genes responsible for producing enzymes known as dicer-like two and dicer-like 4.
According to Ding, without these enzymes, the plant is unable to generate siRNAs to combat viral infections, resulting in non-functional antiviral immune pathways.
Despite the mutant plants growing and producing seeds normally, they exhibited severe symptoms when infected with the cucumber mosaic virus. This led to reduced seed production and a significant tenfold increase in transmission rate to the seeds, with up to 40% of the new seedlings becoming infected.
“We got really excited by this result,” Ding said. “This is the first time anybody has seen this major change in seed transmission after an immune pathway is eliminated.”
The research team aims to address the mystery of how viruses manage to infect a small percentage of seeds in non-mutant plants despite strong immune suppression. Their findings indicate that the virus uses a protein to block the RNA interference pathway in mother plants. Moving ahead, they plan to investigate whether enhancing the identified immune pathway in the seeds can further reduce virus transmission rates.
This discovery has significant implications for disease prevention in both animals and humans, as the identified pathway is widely conserved across various organisms. The research could potentially contribute to the prevention of serious birth defects, including microcephaly and other brain abnormalities, caused by human viruses such as Zika. The team hopes to leverage their findings to mitigate the rate of vertical Zika transmission during pregnancy.
“We know that Zika virus expresses several proteins that block the RNA interference pathway, so it may be possible to prevent vertical transmission by inhibiting the function of these proteins with new drugs.”
Journal reference:
- Si Liu, Shou-Wei Ding. Antiviral RNA interference inhibits virus vertical transmission in plants. Cell Host & Microbe, 2024; DOI: 10.1016/j.chom.2024.08.009
