Characterization of the exocyst complex SEC15 subunit in A. thaliana

The final step of secretion termed exocytosis is mediated by the exocyst complex. The exocyst is an evolutionary conserved protein complex that tethers secretory vesicle to the target membrane and consists of eight subunits: Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo84, and Exo70. Sec15 exocyst subunit was previously shown to connect the rest of the exocyst complex with a secretory vesicle in yeast, mammals and fruit fly via interaction with Rab GTPase and GEF of Rab GTPase. Here, I show that plant SEC15B potentially functions in evolutionary conserved manner. First, two mutant lines of Arabidopsis thaliana sec15b mutant were tested in characteristics typical for other exocyst mutants. Although some characteristics reach certain level of plasticity, both sec15b-1 and sec15b-2 show similar tendencies, which are mostly consistent with defects with other mutants in exocyst subunits. sec15b-1 has been determined as a stronger allele that is defective in formation of seed coat, elongation of etiolated hypocotyl, growth of stem and primary root, establishment of axillary branches and lateral roots, diameter of rosette and, unexpectedly, growth of pollen tubes. Phenotype of sec15b-1 was rescued by insertion of SEC15B gene under SEC15B promotor. Second, complementation test showed that SEC15B and SEC15A are..