Abstract Developmental programmed cell death (dPCD) in Arabidopsis thaliana is an integral part of the differentiation process of the root cap, a specialized organ surrounding meristematic stem cells. dPCD in lateral root cap (LRC) cells depends on the transcription factor ANAC033/SOMBRERO (SMB) and is followed by rapid cell-autonomous corpse clearance, involving the senescence-associated nuclease BFN1 downstream of SMB. Based on transcriptomic analyses, we observed the downregulation of BFN1 during colonization of A. thaliana by the beneficial root endophyte Serendipita indica . Roots of smb3 mutants, deficient in root cap dPCD and corpse clearance, are covered by uncleared LRC cell corpses and hypercolonized by S. indica from the root tip upwards. The bfn1-1 mutant exhibits an attenuated delayed corpse clearance phenotype, but still enhances colonization by S. indica . These results highlight that the constant production and clearance of LRC cells, in addition to its function in root cap size control, represents a sophisticated physical defense mechanism to prevent microbial colonization in close proximity to meristematic stem cells. Furthermore, we propose a mechanism by which S. indica manipulates dPCD in A. thaliana roots by downregulating BFN1 to promote fungal colonization through delayed clearance of dead cells, which present potential sources of nutrients.

Root cap cell corpse clearance limits microbial colonization inArabidopsis thaliana