Plant metabolism: Zoom in to the single-cell level

Plant specialized metabolism is intricately regulated and often compartmentalized at the cell-type level. Understanding where and when metabolites accumulate is essential for uncovering their function, biosynthesis, and regulation. Historically, studies have inferred metabolite localization based on the expression patterns of genes encoding biosynthetic enzymes, but these approaches fall short due to the complexity of metabolite transport and the discrepancy between transcript, protein, and metabolite abundance. Recent advances in mass spectrometry imaging, single-cell transcriptomics, and multiomics have enabled the direct visualization and quantification of metabolites and gene expression at cellular resolution. These technologies have revealed striking cell type- and organ-specific patterns of metabolite accumulation, as well as the underlying transcriptional and chromatin regulatory networks. In this review, we describe case studies in several model and medicinal plant species that highlight the roles of rare or specialized cell types in specialized metabolite biosynthesis and the importance of spatiotemporal regulation. In addition, we discuss why it is becoming increasingly important to transition from single- to multiomics approaches. As new tools continue to evolve, the regulation of plant metabolism will be uncovered at higher resolution, enabling precise pathway discovery and metabolic engineering for agriculture, biotechnology, and medicine.