Seminars

 Secondary growth of plant shoots and roots is a stem cell-driven process fundamental for the mechanical and physiological support of enlarging plant bodies. In most dicotyledonous species, the underlying stem cell niche, the cambium, generates xylem toward the organ centre and phloem toward the organ periphery. However, how cambium stem cell (CSC) homeostasis and related cell fate decisions are regulated is largely unknown. To uncover cambium organization, we have revealed cellular lineage of CSC (Shi et al., Development 2019) and tissue specific transcriptional state using nucleus RNA-seq (Shi et al., Plant Cell, 2021).
 Nuclei can be easily extracted in the combination with Fluorescence-Activated Nuclei Sorting (FANS) and provided sufficient RNA for cell identification. Recently, we have further developed our method and specifically revealed the transcriptome of bifacial cambium stem cells and differentiating xylem and phloem cells using single nucleus (sn) RNA-seq analysis. Our analysis revealed that cambium stem cells have a unique transcriptional status which is different from differentiating cells. In combination with a plate-based method, our method enabled us to analyse not only the noisy gene expression data of each nucleus, but also the relatively stable fluorescent signals representing specific gene expression of interest, as well as the ploidy of each nucleus at a single nucleus resolution. Furthermore, our dataset enabled us to estimate the spatial distribution of phytohormonal pathway responses during the secondary growth and we revealed an uncharacterized function of phytohormonal pathway regulating xylem vessel formation. Based on the obtained transcriptome dataset and tissue specific gene modulation, we want to uncover the cellular mechanism behind the secondary growth.