Root Type-specific Establishment of Postembryonic Stem Cell Niches during Maize Lateral Root Formation

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Lateral roots are established from pericycle stem cell niches of other roots. In maize, phloem pole pericycle cells give rise to lateral roots, while in Arabidopsis lateral roots emerge from xylem pole pericycle cells. Maize forms different root types at different stages of development. Root type-specific developmental control of lateral root formation in maize is demonstrated, for example, by the mutant rootless with undetectable meristem 1 (rum1), which does not form lateral roots in the primary root, while lateral root formation in the shoot-borne root-system is not affected.The overreaching hypothesis of this project is that the establishment of lateral root stem cell niches involves conserved and distinct players in the different root types of maize. In this project, we will (i) study the cellular organization of lateral root stem cell niches in the different main root types of maize during early development. Moreover, we will (ii) elucidate the plasticity of gene expression networks in phloem and xylem pole pericycle cells during early stem cell niche establishment in the main maize root types of wild-type and the mutant rum1. This will be achieved by a combination of laser capture microdissection (LCM) of these cells in combination with RNA-seq. Subsequently, we will analyze the regulation of the transcriptomic landscape of these cell types with respect to developmental stage, genotype and root type. Finally, we aim to (iii) identify and characterize novel root type-specific genetic regulators of lateral root stem cell niche establishment. To this end we will characterize mutants of candidate genes identified in the RNAseq experiment via our reverse genetic mutant repository which covers ca. 60% of all maize genes. Novel lateral root mutants identified in our collection will be further characterized to better understand the molecular framework underlying root type-specific regulation of lateral root stem cell niche establishment.