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Virus-Free Plants, A Mystery Solved

Researchers at the University of Science and Technology of China (USTC) uncover new insights to pathogen-free plants.

Plant stem cells, or undifferentiated plant cells known as meristematic cells give plants the ability to continuously grow through cell division. These cells have similar properties to totipotent stem cells which have the special ability to transform themselves into different specialised cell types of the plant. Meristematic cells are triggered when required and can produce any type of plant cell when needed. These cells exist at the tips of all plants, enabling them to grow new stems or roots, and for trees, the trunk when needed.

The ability of the meristems at the tip of plants to remain virus-free is remarkable even though it has been infected by a foreign organism and has been noted since the 1950s. This antiviral ability of a plant has been exploited by scientists and farmers since then for the cultivation of new plants from donor plants that are infected. They simply snip a tiny part of the tip, culture it in a test tube or petri dish over a period of time and the plant cutting typically grows pathogen-free.

In a recent study published in Science by the researchers at USTC have offered new insights into this incredible virus-free ability of plants. The research team inoculated a thale cress plant (Arabidopsis thaliana, related to cabbage and mustard, often used in botanical research as a model organism) with Cucumber Mosaic Virus and watched what happened.

The virus spread towards the tip of the plant and then stopped just before the region known as the WUSCHEL-expression domain. Upon further examination at the distribution of WUSCHEL regulator proteins at this region, the team found that the was high levels of protein where the virus had spread to.

WUSCHEL protein is a transcription factor that plays a regulatory role in determining stem cell fate, at the early stages of the development of a plant embryo. It also oversees the meristematic cells by maintaining them in an undifferentiated state and specifying the type of daughter cells they will produce.

“There’s a chemical called dexamethasone that can induce production of these WUSCHEL proteins in our tested plants,” said Zhao Zhong, paper author and a professor from the School of Life Science at USTC, “next, we inoculated more cress with the virus and then gave some of the plants dexamethasone treatment, and some we just left alone.” 89 percent of the plants without the treatment were infected with the virus, but 90 percent of those with the treatment were free from virus invasion.

The research team then discovered that it was the work of WUSCHEL proteins that prevented the production of viral proteins. When infected by the virus, WUSCHEL proteins halts all protein production to prevent the virus from taking over the plant cell’s mechanisms to produce its own proteins for replication.

Genes similar to those that direct production of WUSCHEL proteins in the thale cress are very widespread across the plant kingdom, so the researchers are looking into “whether this strategy can be applied in breeding to obtain broad-spectrum antiviral crop varieties in the future” says Professor Zhao. [APBN]