Characterization of Multiple C2 Domain and Transmembrane Region Proteins in Arabidopsis

Multiple C2 domain and transmembrane region proteins (MCTPs) are evolutionarily conserved in eukaryotic organisms and may function as signaling molecules that mediate trafficking of other regulators. Although there are a large number of MCTPs found in the plant lineage, biological information on most plant MCTPs remains unknown. Here, we report systematic characterization of 16 members in the entire Arabidopsis (Arabidopsis thaliana) MCTP family. Using GUS and GFP reporter assays, we reveal their distinct or overlapping patterns of gene expression and protein localization in developing Arabidopsis plants and Nicotiana benthamiana leaf epidermal cells. We further analyze in vivo effects of three C2 domains on the regulatory role of MCTP1 (FTIP1) in flowering time control in Arabidopsis, demonstrating that these C2 domains may be cooperative to mediate FTIP1 function during the floral transition. Through examining all available T-DNA insertional mutants of Arabidopsis MCTPs, we further reveal that mctp6-1 significantly enhances the late-flowering phenotype of ftip1-1 possibly through affecting FLOWERING LOCUS T in different manners, exemplifying that different MCTPs additively regulate a specific plant developmental process. Taken together, our results suggest functional divergence or redundancy of MCTP members in Arabidopsis and provide a community resource for further understanding various MCTP functions in plant development.