Plant viruses as next-generation vectors for transgene-free genome editing, gene regulation, and rapid crop improvement.

Plant viruses, which were previously considered only as agricultural threats, are becoming programmable vectors of transgene-free, tissue culture-independent genome editing. Engineered viral vectors can be used to precisely deliver genome-editing reagents far more expeditiously than classical techniques by harnessing their inherent ability to replicate and disseminate throughout the systemic space. These systems are 5-10 times faster to accomplish trait validation and overcome the tissue culture bottleneck, which continues to inhibit genome editing in more than 80% of crop species today. Viruses have now been used for gene engineering in the new forms of Virus-Induced Gene Silencing (VIGS), Virus-Induced Genome Editing (VIGE), and Virus-Induced Flowering (VIF) to achieve extraordinary efficiency in a broad spectrum of crops, including wheat, maize, rice, barley, potato, and tomato. Virus-based methods are often transgene-free and are usually faster and more versatile than traditional methods of gene editing, and do not require tissue culture. They can be used to improve yield, initiate flowering, enhance biotic and abiotic stress resistance, and enhance nutrition. Although there are some challenges that include limited cargo capacity, not being a Shoot apical meristem (SAM), host specificity, and biosafety concerns. The continuous advances in the design of viral vectors, their combination with miniature genome editors, and technologies of transgene-free editing are enlarging their applications. Collectively, these novel technologies reinvent plant viruses as versatile biotechnological systems to achieve rapid, scalable, and eco-friendly improvements in crops, which can offer a way of agriculture free of transgenes and able to be delivered worldwide.