Scientists discover how plants prevent the transmission of viruses to future generations

Scientists have discovered how plants prevent viruses from being transmitted to their seeds. The discovery could ensure healthier crops and reduce the transmission of diseases from mother to offspring in both plants and humans. The study by scientists at the University of California, Riverside, reveals that RNA interference is the key to blocking the spread of viruses in plants during seed development.

Plant viruses can spread internationally through the seed trade. The problem of transmission of viruses from parent plants to their seeds, known as vertical transmission, is a global concern in agriculture. This is due to the ability of viruses to remain "hidden" in seeds for years, causing serious epidemics when infected plants grow.

The study, led by Professor Shou-Wei Ding of UC Riverside’s Department of Microbiology and Plant Pathology, sought to understand why only a small percentage of infected plant seeds are affected by viruses. To address this question, the team focused on the immune pathway that prevents virus transmission.

The team tested hundreds of varieties of the plant Arabidopsis thaliana, infecting them with the cucumber mosaic virus. This virus affects more than a thousand plant species and causes yellow spots and rings on leaves and fruits. The analysis identified two crucial genes that activate the RNA interference process, which blocks the production of viral proteins in plants.

These genes are functional only in the early stages of seed development. They produce essential enzymes called dicer-like 2 and dicer-like 4, which generate small fragments of RNA, known as siRNA. These fragments are responsible for inhibiting the production of viral proteins, preventing infection.

When scientists engineered plants so that they did not produce these enzymes, the result was more severe viral infection and a tenfold increase in virus transmission to seeds. Up to 40 percent of new seedlings became infected, demonstrating the direct impact of RNA interference on plants’ immune defenses.

The study also investigated why, even in plants with strong immune defenses, a small percentage of seeds still become infected. They found that some viruses produce proteins that block the RNA interference pathway. The next step in the research will be to try to boost this immune pathway, aiming to further reduce viral transmission rates.

The discovery has broad implications, as RNA interference is a conserved mechanism in many organisms, including invertebrates, fungi and mammals. In addition to benefiting agriculture, scientists hope the research will help prevent the transmission of human viruses such as Zika, which causes severe birth defects when transmitted from mother to child.

The discovery paves the way for the development of new strategies to protect crops and control the spread of viral diseases, both in plants and animals.

More information can be found at doi.org/10.1016/j.chom.2024.08.009