Technical advances for analyzing spatially specific circadian rhythms. Tissue-specific circadian rhythms can be measured using thermal imaging (top left) (Dakhiya and Green, 2019) and luciferase imaging. Spatial studies of clock gene expression can be enhanced by tissue-specific split luciferase assays (box, left). One construct, expressed under a circadian promoter, comprises the C-terminal half of luciferase fused to the C-terminus of A-Fos. A second construct consisting of the N-terminal half of luciferase fused to the bZIP domain of c-Jun is constitutively expressed under a tissue-specific promoter (either directly or indirectly through a UAS promoter transactivated by enhancer trap-driven expression of GAL4; Román et al., 2020). When both constructs are expressed together, the A-Fos and c-Jun domains facilitate dimerization, bringing the two halves of luciferase into close proximity to reconstitute enzymatic activity (Endo et al., 2014), generating luminescence from circadian rhythms only in a target tissue (e.g. root). Single-cell clock functions can be studied with transcriptional (e.g. CCA1::YFP) or translational (e.g. CCA1::CCA1-YFP) fluorescent reporters (top right) and single-cell RNA-seq (bottom right). Clustering of single-cell transcriptomes at separate time points provides extra information on circadian regulated functions in specific cell types (Apelt et al., 2021).