Root cap cell corpse clearance limits microbial colonization in Arabidopsis thaliana

Abstract

Programmed cell death occurring during plant development (dPCD) is a fundamental process integral for plant growth and reproduction. Here, we investigate the connection between developmentally controlled PCD and fungal accommodation in Arabidopsis thaliana roots, focusing on the root cap-specific transcription factor ANAC033/SOMBRERO (SMB) and the senescence-associated nuclease BFN1. Mutations of both dPCD regulators increase colonization by the beneficial fungus Serendipita indica , primarily in the differentiation zone. smb-3 mutants additionally exhibit hypercolonization around the meristematic zone and a delay of S. indica -induced root-growth promotion. This demonstrates that root cap dPCD and rapid post-mortem clearance of cellular corpses represent a physical defense mechanism restricting microbial invasion of the root. Additionally, reporter lines and transcriptional analysis revealed that BFN1 expression is downregulated during S. indica colonization in mature root epidermal cells, suggesting transcriptional control as a means for microbial regulation of host dPCD. The process of programmed cell death in root development (dPCD) influences the extent and outcomes of fungal symbiosis Fungal colonization of the root tip and differentiation zone is restricted by SMB-mediated clearance of dead cells, which preserves the meristem and regulates symbiosis The plant nuclease BFN1, which is associated with senescence, is exploited by beneficial microbes to facilitate their root accommodation