mTACT: A cell type–specific transportome-scale amiRNA toolbox to overcome functional redundancy in Arabidopsis

In plants, both developmental processes and environmental responses are spatiotemporally regulated by an assembly of signaling molecules such as hormones, secondary metabolites, and ions. The ability of these signaling molecules to move within and across plant tissues is essential for various developmental cues. However, the characterization of transported signaling molecules and their translocation mechanisms is difficult due to the functional redundancy of plant genomes and shortcomings in methodologies. Here, we report our development of the Multi Targeted AmiRNA Cell type–specific Transportome-scale (mTACT) toolbox, which can be used to reveal phenotypic plasticity in plants. mTACT is based on a large set of artificial microRNAs (amiRNAs), each designed to optimally target multiple members of a particular gene family encoding transporter proteins. In total, the mTACT toolbox includes 5,565 amiRNAs, targeting 81.7% of the Arabidopsis (Arabidopsis thaliana) transportome. The amiRNA library can be driven under 12 cell type– specific promoters, allowing the design of spatial-specific genetic screens. mTACT is further divided into 8 sublibraries of amiRNAs targeting a functionally defined protein class. A proof-of-concept screen validated the mTACT approach by identifying phenotypes linked to both known and unidentified genes. With the ability to overcome functional redundancy in a transportome-scale, cell type– specific manner, the mTACT toolbox will allow the plant research community to study previously hidden genetic factors required for long-and short-distance translocation of signaling molecules.