To identify genes that play critical roles during male gametogenesis in Arabidopsis, we have isolated several pollen morphological mutants from a mutagenized seed pool generated with a T-DNA activation vector. In this study, we have focused on a mutant plant producing ~50% abnormal pollen grains including high levels of collapsed pollen at maturity. The pollen developmental analysis showed that the mutant pollen phenotype was first observed at tricellular stage. Interestingly, the mutation was only maintained as a heterozygote due to the severely reduced genetic transmission through both sexes. TAIL PCR analysis led to the identification of the responsible gene which encodes a conserved oligomeric golgi complex component-related protein (COGCC). RT-PCR analysis showed predominant expression of the gene in reproductive organs including developing spores. The gene identity was confirmed by the result that mutant plants harboring a T-DNA containing corresponding wild type gene produced less level of mutant pollen grains. Furthermore, confocal laser scanning microscopy using mature pollen expressing COGCC-RFP driven under the native promoter showed small punctate signals, which are likely to be from the Golgi complex. Further experiments for co-localization of the COGCC-RFP with the Golgi markers are underway.