Transgenerational antiviral barrier in plants

Plant viruses account for large losses in crop yields every year. While plant virology is an important field of plant-pathogen interaction, studied since more than 100 years, several core aspects of plant- virus interaction remain poorly understood. One of them is the observation that many pathogenic viruses cannot enter plant apical meristems, organs containing the stem cells necessary for plant survival, growth and reproduction. It is believed that exclusion from meristems can prevent viruses from entering the gametes and resulting progeny. Little is known about the molecular events responsible for this antiviral barrier, which has evident biological and economic significance. The objective of this project is to investigate exclusion of viruses from meristem and progeny through a series of cutting-edge molecular approaches, while laying the experimental bases for long-term research on the topic. We will use the model plant species Arabidopsis thaliana, to benefit from its established advantages during experimental manipulation and investigation of complex biological mechanisms. We will generate and use a variety of fluorescent reporter viruses to observe virus movement and antiviral defense in plants during infection. We will interfere with plant defenses specifically in meristematic and gametic cells and ask if this leads to virus invasion into reproductive tissues and virus transmission to progeny. We will determine which genes are switched on and off in stem cells during infection, to identify which factors are involved in the antiviral barrier. Rapid assays to determine rates of virus transmission to plant progeny will also be developed. With these experimental approaches, we expect to contribute to future development of antiviral strategies in agriculture.

Plants possess, at the tips of their growth points, very important organs called meristems. These contain stem cells that generate new tissues and organs throughout the growth of the plant. When a plant forms flowers, these stem cells will eventually give rise to male and female gametes, which, once fertilized, will form an embryo and thus the next generation. However, meristems also have a role in defense against viruses. Although virus infections can be devastating to plants, remarkably many pathogenic viruses are somehow prevented from infecting the stem cells in meristems. This is believed to contribute to the ability of infected plants to generate progeny that is mostly - or totally - virus free. How the plant's defense against viruses works in the meristem is poorly understood. Through the work funded by the FWF we were able to show, through several experimental approaches, that plants use a defensive mechanism called RNA interference to prevent viruses from infecting their stem cells and progeny. We found that plants use small RNA molecules produced in infected tissue to provide their stem cells with the genomic sequence information of the invading virus. This allows the stem cells to efficiently prevent infection upon virus arrival. Furthermore, we found this mechanism to be activated by the plant hormone salicylic acid, which in this case acts as a kind of alarm bell. During the funding period, we developed many biological tools and special microscopy techniques for further investigations. Hopefully, these will lead to novel ways to combat seed transmission of viral diseases in crop species, contributing to food security worldwide.