<scp>SLCMV</scp> ‐Encoded <scp>BC1</scp> Protein Suppresses Photosynthesis by Disrupting Chloroplast Structure and Gene Expression

Sri Lankan cassava mosaic virus (SLCMV) is a highly destructive plant virus that poses a significant threat to cassava cultivation. It causes severe symptoms, including distinctive leaf mosaic patterns and stunted plant growth. Here, transcriptome sequencing revealed that SLCMV infection induced widespread transcriptional reprogramming, with 10,164 differentially expressed genes-6910 up-regulated and 3254 down-regulated. Notably, the down-regulated genes were primarily associated with plant chloroplast components and photosynthesis pathways. Reverse transcription-quantitative PCR analysis confirmed the suppression of key genes involved in photosystem I (PSI) and photosystem II (PSII). Further investigation revealed that SLCMV infection disrupted chloroplast ultrastructure and reduced total chlorophyll content, thereby inhibiting photosynthetic capacity in Nicotiana plants. Importantly, our findings highlighted the critical role of the SLCMV-encoded BC1 protein in repressing photosynthesis-related gene expression and attenuating overall photosynthetic activity. SLCMV-encoded movement protein BC1 down-regulates the expression of photosynthesis-related genes and disrupts chloroplast structure, ultimately leading to reduced photosynthetic activity.