Fluorescence-Activated Cell Sorting Using the D-Root Device and Optimization for Scarce and/or Non-Accessible Root Cell Populations

Fluorescence-activated cell sorting (FACS) is a technique used to isolate specific cell populations based on characteristics detected by flow cytometry. FACS has been broadly used in transcriptomic analyses of individual cell types during development or under different environmental conditions. Different protoplast extraction protocols are available for plant roots; however, they were designed for accessible cell populations, which normally were grown in the presence of light, a non-natural and stressful environment for roots. Here, we report a protocol using FACS to isolate root protoplasts from Arabidopsis green fluorescent protein (GFP)-marked lines using the minimum number of enzymes necessary for an optimal yield, and with the root system grown in darkness in the D-Root device. This device mimics natural conditions as the shoot grows in the presence of light while the roots grow in darkness. In addition, we optimized this protocol for specific patterns of scarce cell types inside more differentiated tissues using the mCherry fluorescent protein. We provide detailed experimental protocols for effective protoplasting, subsequent purification through FACS, and RNA extraction. Using this RNA, we generated cDNA and sequencing libraries, proving that our methods can be used for genome-wide transcriptomic analyses of any cell-type from roots grown in darkness.