Engineering Artificial MicroRNAs for Multiplex Gene Silencing and Simplified Transgenic Screen.

Artificial microRNA (amiRNA) technology offers reversible and flexible gene inactivation and complements genome-editing technologies. However, obtaining transgenic plants with maximal gene silencing remains a major technical challenge in current amiRNA applications. Here, we incorporated an empirically determined feature of effective amiRNAs to the amiRNA design and in silico generated a database containing 533,429 gene-specific amiRNAs for silencing 27,136 genes in Arabidopsis (Arabidopsis thaliana), with a genome coverage of 98.87%. In both single-gene and multiple-gene silencing, we observed an overall improvement in performance by amiRNAs designed using our strategy in Arabidopsis protoplasts and transgenic plants. In addition, the endogenous tRNA-processing system was used to generate multiple amiRNAs from tRNA-pre-amiRNA tandem repeats for multiplex gene silencing. An intronic amiRNA-producing fluorescent reporter was explored as a visual screening strategy for transgenic Arabidopsis and rice (Oryza sativa) plants with maximal whole-plant or cell type-specific gene silencing. These improvements enable the amiRNA technology to be a functional gene knockout tool for basic and applied plant research.