Abstract
Insect-vectored plant viruses pose a serious threat to sustainable production of economically important crops worldwide. This demands a continuous search for environmentally-friendly, sustainable and efficient approaches based on biological agents to address the mounting challenges of viral disease management. To date, the efficacy of actinomycetes bacteria against DNA plant viruses remains unknown. Here, through comparative analyses, we demonstrate that the RFS-23 strain of Streptomyces cellulase possesses protective activity as it positively regulated the plant growth and development and diminished the severity, of disease symptoms, together with reduced accumulation of Tomato yellow leaf curl virus (TYLCV) DNA. The RFS-23 strain maintained relative chlorophyll contents by promoting the expression of genes (CLH1, HEMA1 and PORA) associated with chlorophyll biogenesis. As compared to another strain, CTF-20, the RSF-23 induced a significantly higher expression of plant defense-related genes (NbCIS and NbNCED) associated with biogenesis and accumulation of salicylic acid and abscisic acid. Additionally, the activity of antioxidant enzymes (SOD, CAT, POD and MDA) was significantly enhanced by RSF-23 treatment, despite the presence of viral infection. These findings suggest that RSF-23 is a novel biocontrol agent with protective activity, and it could be a potential candidate for the management of plant viral infections.