A Missense Mutation in the NSF Gene Causes Abnormal Golgi Morphology in Arabidopsis thaliana.

The Golgi apparatus is a key station of glycosylation and membrane traffic. It consists of stacked cisternae in most eukaryotes. However, the mechanisms how the Golgi stacks are formed and maintained are still obscure. The model plant Arabidopsis thaliana provides a nice system to observe Golgi structures by light microscopy, because the Golgi in A. thaliana is in the form of mini-stacks that are distributed throughout the cytoplasm. To obtain a clue to understand the molecular basis of Golgi morphology, we took a forward-genetic approach to isolate A. thaliana mutants that show abnormal structures of the Golgi under a confocal microscope. In the present report, we describe characterization of one of such mutants, named #46-3. The #46-3 mutant showed pleiotropic Golgi phenotypes. The Golgi size was in majority smaller than the wild type, but varied from very small ones, sometimes without clear association of cis and trans cisternae, to abnormally large ones under a confocal microscope. At the ultrastructual level by electron microscopy, queer-shaped large Golgi stacks were occasionally observed. By positional mapping, genome sequencing, and complementation and allelism tests, we linked the mutant phenotype to the missense mutation D374N in the NSF gene, encoding the N-ethylmaleimide-sensitive factor (NSF), a key component of membrane fusion. This residue is near the ATP-binding site of NSF, which is very well conserved in eukaryotes, suggesting that the biochemical function of NSF is important for maintaining the normal morphology of the Golgi.Key words: Golgi morphology, N-ethylmaleimide-sensitive factor (NSF), Arabidopsis thaliana.