Satellite RNAs of Cucumber Mosaic Virus: Molecular Features, Pathogenic Roles, and Ecological Dynamics.

Cucumber mosaic virus (CMV) is one of the most widespread and economically important plant viruses, infecting over 1,300 species across diverse plant families. A distinctive feature of CMV biology is its association with satellite RNAs (satRNAs), small non-coding RNA molecules that rely entirely on the helper virus for replication, encapsidation, and transmission. Despite lacking coding potential, satRNAs profoundly modulate CMV pathogenicity by influencing viral accumulation, symptom expression, and host-virus interactions. Depending on their sequence and structure, satRNAs may intensify symptoms or attenuate disease severity. Their activities are mediated through structural mimicry, RNA silencing pathways, and competition for replication machinery. Beyond molecular interactions, satRNAs also shape ecological and evolutionary outcomes of CMV epidemics, including symptom diversity, host adaptation, and vector transmission dynamics. This review emphasizes current knowledge on the biology, symptom modulation, molecular mechanisms, ecological roles, and detection strategies of CMV satRNAs, while highlighting their significance in viral evolution and disease epidemiology.