Insights into the role of the C4 protein of the geminivirus TYLCSV in transgenic tomato plants

We previously reported that tomato yellow leaf curl Sardinia virus (TYLCSV), a begomovirus belonging to the Geminiviridae family, confers enhanced tolerance to drought in tomato plants. This higher resilience has been attributed to the virus-encoded C4 protein, of small and highly variable protein, to which a multitude of roles have been attributed, from virus movement to RNA silencing suppression, symptom development, and plant defense. Indeed, transgenic tomato plants overexpressing the TYLCSV C4 protein showing morphological defects were resistant to drought and fungal attack. To define the molecular basis potentially responsible for the phenotype of C4 plants, an RNA-Seq analysis was carried out comparing plants overexpressing C4 with wild-type individuals. Differential expression (DE) analysis, followed by Gene Ontology and KEGG pathway enrichment analysis revealed the impact of C4 protein on the metabolism of nucleotides, starch, glucose, cell wall components, fatty acids, and plant hormones and on pathogen interaction. Additionally, we conducted biomolecular analyses using RT-qPCR to study the expression of key genes known to be involved in cell wall-related pathways. This work contributes to shed light on the intricate interplay between geminiviruses and tomato plants under abiotic and biotic stresses.