Ohtomo Ichiro, Ueda Haruko, Shimada Tomoo, Nishiyama Chiaki, Komoto Yasuko, Hara-Nishimura Ikuko, Takahashi Taku
Division of Biological Sciences, Graduate School of Science, Hokkaido University, N10 W8, Sapporo, 060-0810 Japan.
Plant Cell Physiol. 2005 Aug;46(8):1358-65. doi: 10.1093/pcp/pci146. Epub 2005 Jun 4.
The short stem and midrib (ssm) mutants of Arabidopsis thaliana show both semi-dwarf and wavy leaf phenotypes due to defects in the elongation of the stem internodes and leaves. Moreover, these abnormalities cannot be recovered by exogenous phytohormones. ssm was originally identified as a single recessive mutant of the ecotype Columbia (Col-0), but genetic crossing experiments have revealed that this mutant phenotype is restored by another gene that is functional in the ecotype Landsberg erecta (Ler) and not in Col-0. Map-based cloning of the gene that is defective in ssm mutants has uncovered a small deletion in the sixth intron of a gene encoding a syntaxin, VAM3/SYP22, which has been implicated in vesicle transport to the vacuole. This mutation appears to cause a peptide insertion in the deduced VAM3/SYP22 polypeptide sequence due to defective splicing of the shortened sixth intron. Significantly, when compared with the wild-type Ler genome, the wild-type Col-0 genome has a single base pair deletion causing a frameshift mutation in SYP23, a gene with the highest known homology to VAM3/SYP22. These findings suggest that VAM3/SYP22 and SYP23 have overlapping functions and that the vesicle transport mediated by these syntaxins is important for shoot morphogenesis.
拟南芥的短茎和中脉（ssm）突变体由于茎节间和叶片伸长缺陷，表现出半矮化和叶片卷曲的表型。此外，这些异常不能通过外源植物激素恢复。ssm最初被鉴定为生态型哥伦比亚（Col-0）的单隐性突变体，但遗传杂交实验表明，该突变体表型可被另一个在生态型直立型兰茨贝格（Ler）中有功能而在Col-0中无功能的基因恢复。对ssm突变体中缺陷基因的图位克隆揭示了一个编码 syntaxin的基因VAM3/SYP22的第六个内含子中有一个小缺失，该基因与液泡的囊泡运输有关。由于缩短的第六个内含子剪接缺陷，这种突变似乎导致了推导的VAM3/SYP22多肽序列中的肽插入。值得注意的是，与野生型Ler基因组相比，野生型Col-0基因组有一个单碱基对缺失，导致SYP23发生移码突变，SYP23是与VAM3/SYP22已知同源性最高的基因。这些发现表明，VAM3/SYP22和SYP23具有重叠功能，并且这些syntaxin介导的囊泡运输对茎形态发生很重要。
