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

侧根是由其他根的中柱鞘干细胞壁龛建立的。在玉米中，韧皮部极中柱鞘细胞产生侧根，而在拟南芥中，侧根由木质部极中柱鞘细胞产生。玉米在不同发育阶段形成不同的根系类型。对玉米侧根形成的根型特异性发育控制得到了证明，例如，分生组织1检测不到的无根突变体（rum1）在主根中不形成侧根，而在芽生根系中侧根的形成不受影响。这个项目的过度假设是侧根干细胞生态位的建立涉及玉米不同根类型中保守的和不同的参与者。在本项目中，我们将(i)研究不同主要根系类型玉米发育早期侧根干细胞壁龛的细胞组织。此外，我们将（ii）阐明野生型和突变体rum1的主要根型在早期干细胞生态位建立过程中韧皮部和木质部极中柱鞘细胞基因表达网络的可塑性。这将通过结合这些细胞的激光捕获显微解剖（LCM）和RNA-seq来实现。随后，我们将分析这些细胞类型在发育阶段、基因型和根型方面的转录组学调控。最后，我们的目标是（iii）鉴定和表征侧根干细胞生态位建立的新型根型特异性遗传调控因子。为此，我们将通过我们的反向基因突变库对RNAseq实验中发现的候选基因的突变进行表征，该库涵盖了所有玉米基因的约60%。在我们的收集中发现的新的侧根突变体将进一步表征，以更好地理解侧根干细胞生态位建立的根类型特异性调控的分子框架。

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.