Symptom Development in Plant Viral Diseases: What, How, and Why?

Plant viruses are obligate intracellular pathogens that hijack host cellular machinery to support their replication and spread. Viral infection induces a variety of structural and physiological changes in the plant as a result of viral biology and its interplay with host processes; these alterations can manifest as visible disruptions of normal growth and development, like stunting, leaf curling, chlorosis, or necrosis, which we recognize as disease symptoms. Despite their significant economic impact, the molecular mechanisms behind symptoms remain poorly understood, and their biological significance is in most cases still unclear. This review explores the possible sources of viral symptoms in plants, their elucidated molecular underpinnings, and the potential implications of symptom development for viral infection and ecology as well as plant health.