ZmDLR9 is required for lateral root development via pre‐rRNA processing in maize

Abstract

SUMMARY Pumilio (PUM) proteins comprise an evolutionarily conserved family of sequence‐specific RNA‐binding proteins that act as key post‐transcriptional regulators in eukaryotes. In this study, we identified a maize PUM protein, named ZmDLR9 (Defective in Lateral Root 9), as a positive factor involved in lateral root development. Loss‐of‐function mutation in the ZmDLR9 (dlr9‐1) severely impaired lateral root formation. Functional analysis revealed that ZmDLR9 localizes in the nucleolus and interacts with pre‐rRNA processing‐associated proteins, including BRX1‐1 (BIOGENESIS OF RIBOSOMES IN XENOPUS 1–1), BRX1‐2, and GRC3 (a subunit of the ITS2 processing complex). The dlr9‐1 mutation resulted in aberrant accumulation of pre‐rRNA processing intermediates, as well as defects in ribosome assembly and translation. Heterologous expression of ZmDLR9 partially rescued the growth defects of an Arabidopsis PUM loss‐of‐function mutant (apum24‐2), demonstrating functional conservation of the PUM protein family across the plant kingdom. Furthermore, the dlr9‐1 mutation disrupted nucleolar morphology, thereby inhibiting cell proliferation and delaying lateral root primordia emergence. Together, our results demonstrate that ZmDLR9, a Pumilio protein, is required for lateral root development by mediating pre‐rRNA processing‐dependent cell proliferation.