Poster: Protein Targeting & Vesicular Trafficking

Abs # 1180: Analysis of an Arabidopsis mutant with a peptide insertion in a syntaxin protein SYP22/AtVAM3

Presenter:	Ohtomo, Ichiro , i-ohtomo@sci.hokudai.ac.jp
Authors	Ohtomo, Ichiro  (A)   Takahashi, Taku  (A)
Affiliations:	(A): Division of Biological Sciences, Hokkaido University

We isolated a semi-dwarf mutant, short stem and midrib (ssm), from a T-DNA transformed population of Arabidopsis thaliana. Since the locus responsible for the mutant phenotype was not linked to the T-DNA insertion, we tried to identify the locus by positional cloning. Sequence determination revealed that the ssm mutant has a small deletion in the 6th intron of SYP22/AtVAM3, a gene encoding a syntaxin. We found that the resulting intron sequence is not spliced and could be translated to 19 amino acids between the 6th exon encoding a juxtamembrane domain and the 7th exon encoding a transmembrane domain. According to a study of the syntaxin 1A with linker insertions to the juxtamembrane domain (McNew et al., 1999), efficiency of the fusion of two docked vesicles has been shown to be decreased by such modifications. Sato et al. (1997) have reported that SYP22/AtVAM3 is localized to the regions on vacuolar membranes where two vacuoles face to each other. Thus, it is possible that the ssm mutant phenotype is attributed to decreased vacuole fusion. The ssm mutant is a single recessive allele in the ecotype Columbia. However, in the process of the genetic analysis, we found that there is another locus that complements the ssm phenotype in the ecotype Landsberg, and that it encodes another syntaxin SYP23. The SYP23 locus in Columbia contains a frame shift mutation and encodes the protein lacking in the C-terminal transmembrane domain.