Root growth is strongly affected by densely colonized microorganisms in the rhizosphere. Consequently, resistance toward pathogenic (hazardous) microorganisms are of particular importance to optimize root growth, and hence plants have evolved various resistance systems to cope with pathogen attack. In the past decades, plant-microbe interaction has been studied mostly using artificial inoculation of microbe suspension to the leaf cells. In more recent years, however, studies using the root and soil microbiome are attracting more attentions, as they likely represent more natural settings.
In order to understand cellular and molecular bases of root-microbe interaction, it is important to investigate which of the root cells (or cell layers) are involved, and when and how they respond to the microbes. However, collaboration between plant pathologists and plant developmental biologists have been limited.
The root cap is literally a cap-like tissue covering the root tip and known to play important roles in directing root growth by sensing gravity vector and secreting metabolites to the rhizosphere. The root cap features a unique developmental behavior in which the outermost layer of the root cap are repeatedly detached from the root tip and dispersed into the rhizosphere. Also implicated for the root cap is a role in root-microbe interaction, though its genetic and molecular bases are not known in detail.
We found that mutations in a key regulatory gene of root cap differentiation impair root resistance to pathogenic fungi. Starting with this finding, we are currently investigating how the root cap cells perceive pathogens to activate signaling cascade leading to the resistance, and how the unique spatial organization and cellular dynamics of the root cap cells act in such mechanisms.