Background: Reverse transcriptase (RT) is central to the replication of retroviruses and pararetroviruses. Objective: This study investigated whether CaMV RT can transcribe complementary DNA (cDNA) from the genomic RNA of a co-infecting RNA virus, Materials and Methods: Cauliflower plants were singly infected with CaMV or CMV, or co-infected with both. Symptom development was monitored. Total DNA was extracted from co-infected plants and subjected to PCR using CMV-specific primers, without an Results: CMV-specific cDNA was successfully amplified directly from the total DNA of the co-infected plants, indicating Conclusions: This study provides the first direct evidence of CaMV RT transcribing a heterologous viral RNA (CMV) into cDNA within plant cells. This interviral activity not only elucidates a mechanism behind the suppression of an RNA virus in a mixed infection but also reveals a novel principle that reflects unexpected genetic interactions of the CaMV RT enzyme substrate due to its flexibility in cDNA synthesis from competitor's RNA, opens new avenues for understanding viral interactions in viral ecology.