Nezames Cynthia D, Ochoa Vanessa, Larsen Paul B
Department of Biochemistry, University of California-Riverside, Riverside, CA 92521, USA.
Funct Plant Biol. 2012 Feb;40(1):67-78. doi: 10.1071/FP12234.
A previously-identified Arabidopsis mutant with hypersensitivity to aluminum, als7-1 was studied further to determine the nature of the mutation and subsequently establish the biochemical basis of the increase in Al sensitivity. Physiological analysis revealed that the Al hypersensitivity phenotype is correlated with increased Al uptake and Al-dependent gene expression, indicating that als7-1 has a defect in an Al-exclusion mechanism. Cloning of the als7-1 mutation showed that it negatively affects the gene encoding the putative nucleolar localised ribosomal biogenesis factor SLOW WALKER2, which is required for normal gametogenesis and mitotic progression. Molecular analysis indicated that Al hypersensitivity in als7-1 is correlated with loss of expression of a factor required for S-adenosylmethionine recycling and reduced levels of endogenous polyamines in the mutant. Further analysis shows that Al-dependent root growth inhibition is reversed by addition of exogenous spermine, which is correlated with a significant reduction in Al uptake by spermine treated roots. Endogenous spermine likely functions to compete with Al3+ for binding to extra- and intracellular anionic sites, which suggests that increased spermine levels may be an effective means to improve root growth in Al toxic acid soil environments.
对之前鉴定的对铝超敏感的拟南芥突变体als7-1进行了进一步研究，以确定突变的性质，并随后建立铝敏感性增加的生化基础。生理分析表明，铝超敏表型与铝吸收增加和铝依赖性基因表达相关，这表明als7-1在铝排斥机制方面存在缺陷。als7-1突变体的克隆表明，它对编码假定的核仁定位核糖体生物发生因子SLOW WALKER2的基因产生负面影响，而该因子是正常配子发生和有丝分裂进程所必需的。分子分析表明，als7-1中的铝超敏性与S-腺苷甲硫氨酸循环所需因子的表达缺失以及突变体内源性多胺水平降低相关。进一步分析表明，添加外源精胺可逆转铝依赖性根生长抑制，这与精胺处理的根对铝吸收的显著减少相关。内源性精胺可能起到与Al3+竞争结合细胞外和细胞内阴离子位点的作用，这表明提高精胺水平可能是改善铝毒酸性土壤环境中根系生长的有效手段。
