Scientists have discovered how plants prevent viruses from transferring to their offspring, a breakthrough that could lead to healthier crops. This finding may also help in decreasing the transmission of diseases from mothers to their children.
Scientists have discovered how plants prevent viruses from being passed on to their offspring, a breakthrough that could result in healthier crops. This finding may also aid in reducing the transmission of diseases from mothers to their children.
Viruses in plants can easily spread from one country to another through the trade of seeds, making the issue of disease transmission from parent plants to their young a significant global concern.
“Viruses can remain dormant in seeds for many years, which makes it a critical issue for agriculture,” explained Shou-Wei Ding, a distinguished professor in the Department of Microbiology and Plant Pathology at UC Riverside. Ding is the lead author of a new study published in the journal Cell Host & Microbe.
When a virus-infected mother plant produces seeds, only about 0 to 5% of the seedlings usually get infected. For over a century, this phenomenon has puzzled scientists, leading them to question how these plants manage to limit the spread of the virus to their offspring.
The research team at UCR aimed to uncover the immune mechanism that blocks virus transmission from parent to offspring, a process known as vertical transmission. They were successful in identifying this mechanism, which is explained in the new paper.
The team tested hundreds of varieties of Arabidopsis, a small member of the mustard family, by infecting them with the cucumber mosaic virus. Despite its name, this virus can threat over 1,000 different plant species, causing yellowing leaves, spotted patterns, and other issues. The researchers then studied the plants to find out which genes contribute to increased resistance against the virus for both the plants and their progeny.
Two specific genes that function primarily during the early phases of seed development were found to be crucial. These genes play a role in the RNA interference pathway.
In cellular processes, the genetic blueprint stored in DNA is translated into RNA, which is subsequently converted into proteins. Sometimes, double-stranded RNA is fragmented into smaller components known as small interfering RNA (siRNA). These siRNA segments work to inhibit the production of certain proteins, some of which are associated with viral invaders.
“Many organisms generate siRNAs to control and reduce viral infections,” Ding stated. “We think these plants can prevent seed infections because the antiviral RNA interference pathway is active during seed development within the mother plants.”
To test their hypothesis, the researchers created mutant plants by eliminating two essential genes linked to the RNA interference pathway. These specific genes are responsible for forming enzymes called dicer-like 2 and dicer-like 4.
“Without these enzymes, the plants are unable to produce siRNAs to fight off viral infections. And without siRNAs, the antiviral immune pathways cease to function,” Ding noted.
The mutant plants grew and produced seeds just like normal plants. However, when these plants were infected with the cucumber mosaic virus, they exhibited severe symptoms, produced fewer seeds, and alarmingly, the transmission rate of the virus to the seeds increased tenfold – up to 40% of the new seedlings were infected.
“We were thrilled by this finding,” Ding remarked. “This is the first time anyone has observed such a significant change in seed transmission following the removal of an immune pathway.”
The researchers then sought to understand how, despite strong immune defenses in non-mutant plants, a small percentage of seeds could still become infected. They discovered that the virus produces a protein that inhibits the RNA interference pathway in mother plants.
Looking ahead, the research team plans to explore methods to further reduce virus transmission rates by enhancing the immune pathway identified in the seeds.
This pathway is broadly conserved across various life forms, including invertebrates, fungi, and mammals, suggesting the discovery could have significant implications for preventing diseases in both animals and humans.
The researchers are considering human viruses like Zika in their future studies. Zika virus infections during pregnancy can lead to severe birth defects, such as microcephaly and other brain disorders. They hope that insights from their work can help reduce the transmission of Zika from mothers to their babies.
“We know that Zika virus produces several proteins that impede the RNA interference pathway, so it could be feasible to prevent vertical transmission by targeting these proteins with new medications.”
