Role of Bean Yellow Mosaic Virus P1 and HC-Pro in Enhancing Gene Expression and Suppressing RNA Silencing in <i>Nicotiana benthamiana</i>

Potyviruses, a major group of plant viruses, utilize HC-Pro, a multifunctional protein, to suppress RNA silencing, a crucial plant defense mechanism. While HC-Pro’s role in RNA silencing suppression has been studied in several potyviruses, the specific mechanisms and interactions of HC-Pro from bean yellow mosaic virus (BYMV), a potyvirus with a broad host range, remain poorly understood. To address this knowledge gap, this study aimed to investigate the role of P1 and HC-Pro from BYMV in enhancing gene expression and suppressing RNA silencing in <i>Nicotiana benthamiana</i>. The findings revealed that BYMV HC-Pro significantly enhanced reporter transgene expression, likely through the suppression of RNA silencing pathways. This effect was further amplified by the presence of the P1 protein, another viral component. Analysis of HC-Pro mutants revealed that the conserved FRNK box within HC-Pro is crucial for its suppression activity and its ability to enhance gene expression. Furthermore, HC-Pro significantly downregulated the expression of key RNA silencing-related genes, including <i>DCL2</i>, <i>DCL4</i>, <i>RDR6</i>, <i>AGO1-1</i>, <i>AGO1-2</i>, and <i>AGO2</i>. These findings demonstrate that the BYMV P1::HC-Pro complex serves as a potent suppressor of RNA silencing and a promising tool for enhancing gene expression in plants. The results have significant implications for developing novel strategies in plant biotechnology, particularly for the production of high-value recombinant proteins.