An integrated analysis of cell-type specific gene expression reveals genes regulated by REVOLUTA and KANADI1 in the Arabidopsis shoot apical meristem

Author summary The plant hormone auxin promotes the formation of lateral organs such as leaves and flowers in a specific region of the shoot called the peripheral zone. Although the restriction of organogenesis to the peripheral zone is known to depend on the Class III Homeodomain Leucine Zipper (HD-ZIPIII) and KANADI1 (KAN1) genes, the transcriptional pathways downstream of these genes have not been studied in the shoot. In this study we investigate regulatory interactions between REVOLUTA (REV), KAN1 and auxin by developing a cell-type specific transcriptomics approach to analyse gene expression patterns and responses to perturbations. Using this approach, we identify cell-type specific genes that respond to changes in REV and KAN1 expression in the shoot. Our data reveal that while REV promotes auxin-related gene expression over the short term, both REV and KAN1 repress auxin induced genes over the long-term, consistent with their influence on organogenesis. We also identify a common set of genes repressed by REV and KAN1 that promote organogenesis. In the Arabidopsis thaliana shoot apical meristem (SAM) the expression domains of Class III Homeodomain Leucine Zipper (HD-ZIPIII) and KANADI (KAN) genes are separated by a narrow boundary region from which new organs are initiated. Disruption of this boundary through either loss of function or ectopic expression of HD-ZIPIII and KAN causes ectopic or suppression of organ formation respectively, raising the question of how these transcription factors regulate organogenesis at a molecular level. In this study we develop a multi-channel FACS/RNA-seq approach to characterize global patterns of gene expression across the HD-ZIPIII-KAN1 SAM boundary. We then combine FACS, RNA-seq and perturbations of HD-ZIPIII and KAN expression to identify genes that are both responsive to REV and KAN1 and normally expressed in patterns that correlate with REV and KAN1. Our data reveal that a significant number of genes responsive to REV are regulated in opposite ways depending on time after induction, with genes associated with auxin response and synthesis upregulated initially, but later repressed. We also characterize the cell type specific expression patterns of auxin responsive genes and identify a set of genes involved in organogenesis repressed by both REV and KAN1.