MATH domain proteins represent a novel protein family in Arabidopsis thaliana, and at least one member is modified in roots during the course of a plant-microbe interaction

The basidiomycete Piriformospora indica interacts with Arabidopsis roots and mimics an arbuscular mycorrhiza. A MATH [meprin and TRAF (tumour necrosis factor receptor‐associated factor) homology] domain‐containing (MATH) protein at the plasma membrane of Arabidopsis roots is one of the first components to respond to the presence of this fungus. MATH proteins are involved in nodule formation in Medicago and protein degradation in the Arabidopsis cytosol. They exhibit sequence similarities to meprins, extracellular peptidases which cleave (signal) peptides, and to TRAFs, intracellular proteins which interact with receptor kinases at the plasma membrane. Fifty‐nine genes for MATH proteins are present in the Arabidopsis genome. Members of this protein family are predicted to be found in the ER–plasma membrane–extracellular space continuum, in the nucleus–cytosol compartment and in organelles. In this article, we describe this novel class of plant genes. We also use MS‐MS analyses to identify the subcellular localization of individual members of the MATH protein family in Arabidopsis thaliana.