Time-resolved single-cell atlas identifies the spatiotemporal transcription dynamics in vernalization response in Brassica rapa.

Many temperate plants require vernalization, a prolonged low-temperature period, to accelerate flowering. Vernalization is a quantitative process whereby extended cold exposure establishes a stable transcriptional repression, with the degree of silencing correlating with the length of cold treatment. While much is known about the genes regulating this process, the expression dynamics at the single-cell level remain elusive. Using single-cell RNA sequencing, we analyze the vernalization response in Brassica rapa. Our data show that mesophyll cells exhibit the most significant changes in gene expression at low temperatures, whereas vasculature exhibits higher expression levels of flowering-related genes. Mesophyll trajectory analyses suggest that B. rapa plants undergo a biphasic response to chill stress during vernalization. Tissue-wide BrFLC expression changes result from variations in the proportion of expressing cells, supporting the quantitative nature of vernalization through digital cell responses. This study provides valuable resources and insights into the spatiotemporal regulation of flowering during vernalization.