Ground tissue circuitry regulates organ complexity in monocot roots [root meristem scRNA-seq]

Most plant roots have multiple cortex layers that make up the bulk of the organ and play key roles in physiology like flood tolerance and symbiosis. However, little is known about how cortical layers form outside the highly reduced anatomy of the model Arabidopsis. Here we use single-cell RNAseq to rapidly generate a cell-resolution map of the maize root, revealing an alternative configuration of the tissue-formative SHORT-ROOT (SHR) signaling pathway adjacent to the expanded cortex. We show that maize SHR protein is hypermobile, moving at least eight cell layers into the cortex. Higher order SHR mutants in both maize and Setaria have reduced numbers of cortical layers, showing that the SHR pathway controls expansion of cortical tissue in monocots that sets up anatomical complexity and a host of key traits. Expression profiling of the maize root meristem at single-cell resolution was performed usingh high-throughput droplet-based technology.