Ras-like small GTP-binding proteins (GTPases) regulate diverse processes in eukaryotic cells including signal transduction, cell proliferation, cytoskeletal organization and intracellular membrane trafficking. These findings support a partially redundant role for AtRabD2b and AtRabD2c in vesicle trafficking during pollen tube growth that cannot be fulfilled by the remaining AtRabD family members. Both AtRabD2b and AtRabD2c protein localize to Golgi bodies. AtRabD2b and AtRabD2c have different but overlapping expression patterns, and they are both highly expressed in pollen. The shorter siliques in the AtrabD2b/2c double mutant were found to be primarily due to the pollen defects. Compared with wild-type plants, AtrabD2b/2c mutants produce deformed pollen with swollen and branched pollen tube tips.
An AtrabD2b/2c double mutant is also indistinguishable from wild-type plants during vegetative growth however its siliques are shorter than those in wild-type plants.
AtrabD2b and AtrabD2c single mutants have no obvious morphological changes compared with wild-type plants across a variety of growth conditions. Here we report that AtRabD2b and AtRabD2c play important roles in pollen development, germination and tube elongation. Many Rab-like proteins exist in plants, but only a subset have been functionally characterized. Rab GTPases are important regulators of endomembrane trafficking, regulating exocytosis, endocytosis and membrane recycling.
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