Plant virology.

The first infectious agent to bear the name 'virus' was described in 1898: a plant pathogen called tobacco mosaic virus that infects a wide range of plants and results in a yellow mosaic of the leaves. Since then, the study of plant viruses has facilitated new discoveries in both virology and plant biology. Traditionally, research has focused on viruses that cause severe disease in plants used for human and animal food or recreation. However, closer inspection of the plant-associated virome is now revealing interactions that range from pathogenic to symbiotic. Although they are often studied in isolation, plant viruses are usually found as part of a broader community that includes other plant-associated microbes and pests. For example, biological vectors of plant viruses (arthropods, nematodes, fungi, and protists) can facilitate the transmission of viruses between plants in an intricate interaction. To enhance transmission, viruses can induce the plant to 'lure' the vector by modulating plant chemistry and defenses. Once delivered to a new host, viruses are dependent on specific proteins that modify the structural components of the cell to enable transport of viral proteins and genomic material. Links between antiviral plant defenses and key steps in virus movement and transmission are being revealed. Upon infection, a suite of antiviral responses is triggered, including the expression of resistance genes - a favored strategy to control plant viruses. In this primer, we discuss these features and more, highlighting the exciting world of plant-virus interactions.