Capping your occupancy: programmed cell death as a mechanism to restrict microbial colonization of the root tip

Thanks to the continued shedding and renewal of root cap cells, plant roots are able to extend into further reaches within the soil column overcoming physical barriers and potential microbial attacks, or so we assumed. Charura et al. explored the latter hypothesis showing that timely programmed cell death at the root cap confers protective properties to the model plant Arabidopsis. They found that two proteins, SMB and BFN1, are involved in regulating cell death and post-mortem cell removal, and in turn regulate plant-microbe interactions. Loss-of function smb-3 and bfn1-1 mutant roots both revealed an accumulation of cell corpses with aggregated proteins along the root. The authors then tested root colonization of the root endophytic fungus, Serendipita indica, in both mutant plants. The increased, uncleared cell corpses in smb-3 mutant roots induced fungal hypercolonization, while bfn1-1 mutants displayed increased S. indica biomass in later stages of interaction. From these findings, the authors proposed that SMB-mediated cell corpse clearance and BFN1 downregulation facilitates root fungal accommodation. Notably, the authors also inoculated Arabidopsis roots with other beneficial microbes. These interactions also yielded the consistent downregulation of BFN1 showing that this mechanism is a conserved strategy employed by microbes to exert transcriptional control to alter cell death program in plants to improve colonization. (Summary by Marvin Jin @MarvinJYS) eLife 10.7554/eLife.96266.3