Synthetic biology for plant viral diagnostics: application to maize lethal necrosis disease

Plant viruses are a risk to many economically important crops, including maize which serves as a staple food for people throughout the world. Indeed, a current epidemic of maize lethal necrosis (MLN) is affecting food security across eastern and central Africa. The disease results from synergistic interaction between two viruses; maize chlorotic mottle virus (MCMV) and sugarcane mosaic virus (SCMV; or other potyviruses). Rapid detection of disease causal agents is imperative for disease management. Advances in synthetic biology have led to new, reliable and affordable molecular diagnostic tools that overcome the limitations of current diagnostic tools used in agriculture. In 2016, Toehold switch technology was demonstrated for the detection of Zika virus in the developing world where resources are limited. This technology can potentially be used for detection of plant viruses. Using publicly available whole-genome sequences for 43 and 73 global isolates of MCMV and SCMV, respectively, an in silico filtering pipeline was used to identify five MCMV and six SCMV sequences that match the canonical structure of a toehold switch and form the basis for toehold switch construction. An in vitro screen was used to assess the functionality of the MCMV and SCMV toehold switches. In addition, three criteria: performance, sensitivity and stability were used to assess the merit for moving forward in the development of field-based sensors for MLN-viral detection.