Root cap cell corpse clearance limits microbial colonization in <i>Arabidopsis thaliana</i>.

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 <i>Arabidopsis thaliana</i> 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 <i>Serendipita indica</i>, primarily in the differentiation zone. <i>smb-3</i> mutants additionally exhibit hypercolonization around the meristematic zone and a delay of <i>S. indica</i>-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 <i>BFN1</i> expression is downregulated during <i>S. indica</i> colonization in mature root epidermal cells, suggesting a transcriptional control mechanism that facilitates the accommodation of beneficial microbes in the roots.