Proteomic studies of the Arabidopsis TRAPP complexes reveal conserved organization and a novel plant-specific component with a role in plant development

How the membrane trafficking system spatially organizes intracellular activities and intercellular signaling networks is not well understood in plants. The Transport Protein Particle (TRAPP) complexes are known to play key roles in selective delivery of membrane vesicles to various subcellular compartments in yeast and animals, but remain to be fully characterized in plants. Here we interrogate the TRAPP complexes in Arabidopsis using quantitative proteomic approaches. TRS33 is a component shared by all TRAPP complexes in yeast and animals, and the Arabidopsis AtTRS33 is essential for the subcellular dynamics of other TRAPP components. Affinity purification of AtTRS33 followed by quantitative mass spectrometry identified fourteen interacting proteins; these include not only thirteen homologs of all known TRAPP components in yeast and mammals but also a novel protein we named TRAPP-interacting plant protein (TRIPP), which is conserved in multi-cellular photosynthetic organisms. Proteomic and molecular analyses showed that TRIPP specifically associates with the TRAPPII complex and directly interacts with the TRAPPII-specific subunits but not the subunits shared with TRAPPIII. TRIPP co-localizes with a subset of TRS33 compartments, and its localization is disrupted in the mutant. Loss-of-function mutation caused growth and reproductive development defects, including partial photomorphogenesis in the dark. Our study demonstrates that plants possess at least two distinct TRAPP complexes similar to metazoan, and identifies TRIPP as a novel plant-specific component of the TRAPPII complex with important functions in plant growth and development.