Viromics unveils extraordinary genetic diversity of the family Closteroviridae in wild citrus

Our knowledge of citrus viruses is largely skewed toward virus pathology in cultivated orchards. Little is known about the virus diversity in wild citrus species. Here, we used a metatranscriptomics approach to characterize the virus diversity in a wild citrus habitat within the proposed center of the origin of citrus plants. We discovered a total of 44 virus isolates that could be classified into species Citrus tristeza virus and putative species citrus associated ampelovirus 1, citrus associated ampelovirus 2, and citrus virus B within the family Closteroviridae, providing important information to explore the factors facilitating outbreaks of citrus viruses and the evolutionary history of the family Closteroviridae. We found that frequent horizontal gene transfer, gene duplication, and alteration of expression strategy have shaped the genome complexity and diversification of the family Closteroviridae. Recombination frequently occurred among distinct Closteroviridae members, thereby facilitating the evolution of Closteroviridae. Given the potential emergence of similar wild-citrus-originated novel viruses as pathogens, the need for surveillance of their pathogenic and epidemiological characteristics is of utmost priority for global citrus production.