RESUMO
Plant roots can regenerate after excision of their tip, including the stem cell niche. To determine which developmental program mediates such repair, we applied a combination of lineage tracing, single-cell RNA sequencing, and marker analysis to test different models of tissue reassembly. We show that multiple cell types can reconstitute stem cells, demonstrating the latent potential of untreated plant cells. The transcriptome of regenerating cells prior to stem cell activation resembles that of an embryonic root progenitor. Regeneration defects are more severe in embryonic than in adult root mutants. Furthermore, the signaling domains of the hormones auxin and cytokinin mirror their embryonic dynamics and manipulation of both hormones alters the position of new tissues and stem cell niche markers. Our findings suggest that plant root regeneration follows, on a larger scale, the developmental stages of embryonic patterning and is guided by spatial information provided by complementary hormone domains.
Assuntos
Raízes de Plantas/fisiologia , Citocininas/metabolismo , Perfilação da Expressão Gênica , Ácidos Indolacéticos/metabolismo , Células Vegetais , Reguladores de Crescimento de Plantas/metabolismo , Raízes de Plantas/citologia , Sementes , Análise de Célula Única , Nicho de Células-Tronco , Células-Tronco/citologiaRESUMO
The genus Selaginella resides in an early branch of the land plant lineage that possesses a vasculature and roots. The majority of the Selaginella root system is shoot borne and emerges through a distinctive structure known as the rhizophore, the organ identity of which has been a long-debated question. The rhizophore of Selaginella moellendorffii - a model for the lycophytes - shows plasticity to develop into a root or shoot up until 8 d after angle meristem emergence, after which it is committed to root fate. We subsequently use morphology and plasticity to define the stage of rhizophore identity. Transcriptomic analysis of the rhizophore during its plastic stage reveals that, despite some resemblance to the root meristem, rhizophore gene expression patterns are largely distinct from both shoot and root meristems. Based on this transcriptomic analysis and on historical anatomical work, we conclude that the rhizophore is a distinct organ with unique features.
RESUMO
The definition of cell identity is a central problem in biology. While single-cell RNA-seq provides a wealth of information regarding cell states, better methods are needed to map their identity, especially during developmental transitions. Here, we use repositories of cell type-specific transcriptomes to quantify identities from single-cell RNA-seq profiles, accurately classifying cells from Arabidopsis root tips and human glioblastoma tumors. We apply our approach to single cells captured from regenerating roots following tip excision. Our technique exposes a previously uncharacterized transient collapse of identity distant from the injury site, demonstrating the biological relevance of a quantitative cell identity index.