Researchers Find Viral Proteins Collaborate to Bring Down Plants’ Defense “Shields”

A new study has provided fresh insights into how viruses damage plants with the aid of viral proteins. Findings could help in developing tactics to prevent significant losses that these microorganisms often bring about.

Viruses have long been a threat to plants. United Nations’ Food and Agriculture Organization (FAO) says the diseases they cause in plants lead to over a billion dollars in losses globally every year.

This new research, which was led by scientists from the University of Washington, shows that viral proteins work together to enable viruses to penetrate a plant’s defense shields to cause problems. Apart

Viral Pepper Infection

from helping a virus to hijack a host plant, these proteins also aid the occurrence of diseases.

“These silencing suppressor proteins are interacting with each other in a seamless, highly coordinated lockstep dance to help the virus in overcome host defense,” said senior study author Hanu Pappu, who is the Chuey Endowed Chair and Samuel H. Smith Distinguished Professor in the Department of Plant Pathology at WSU.

Researchers found that viruses could no longer move freely when a number of these viral proteins were disabled. This holds promise for how to aid plants in bolstering their defense mechanism.

Pappu and his team published their findings in the journal Frontiers in Plant Science.

Plant defense and viral proteins

The struggle between plants and harmful viruses has been ongoing for millions of years, according to researchers. Plants have over time built a high-level defense system to help them repel these pathogens. They set this machinery in motion once they sense intrusion by viruses.

Pappu explained that plants use RNA interference (RNAi) to restrain viruses. This molecular defense destroys the nucleic acid of invading viruses to keep them from taking control of host cells.

However, viruses are not passive to this defense system of plants. They make molecules, which researchers called silencing suppressor proteins, to contain the RNAi defense of a plant.

Pappu compared what plays out to “Star Trek’s Federation-versus-Klingons.”

“When the plant senses an attack by a virus, its ‘shields’ go up,” he explained. “Viruses are finding ways to lower the shields or slip through them and eventually take over the plant.”

Identifying damaging proteins

Pappu has a special interest in viral proteins that help pathogens damage plants and cause crop losses. His ultimate goal is to find ways to fend off these bugs in plants.

The WSU virologist and his colleagues have been researching geminiviruses, a group of infective agents that rank among the most damaging to crops in many places.

Researchers wanted to find out the specific proteins that suppress plants’ defenses. They sought to understand how possible interactions between viral proteins allow viruses to have a free hand.

Working with researchers from the Indian Agricultural Research Institute, WSU research associate Ying Zhai hone in on a geminivirus called the Croton yellow vein mosaic virus. They were able to discover areas where the suppressor proteins are in cells. The team also found out how they interact with cells to cause symptoms and aid the movement of viruses.

Co-author Dan Mullendore, from WSU, used confocal microscopy to study distinct viral proteins and their locations within host cells.

Typically, viruses produce a single protein with a specific function to attack their hosts. Researchers, however, found that the geminivirus in this study had four distinct proteins. These combine to take down the host’s defense system.

Researchers disabled some of the viral proteins and observed that this halted the spread of the virus in a plant. This finding is promising for helping plants to fight off viruses and, in the end, guarding against crop losses.

Pappu noted that a better understanding of how viruses overcome plants’ defense shields will help researchers devise effective means of tackling them.