Michaelson Louise V, Zäuner Simone, Markham Jennifer E, Haslam Richard P, Desikan Radhika, Mugford Sarah, Albrecht Sandra, Warnecke Dirk, Sperling Petra, Heinz E, Napier Johnathan A
Biological Chemistry Department, Rothamsted Research, Harpenden, Hertshire AL5 2JQ, United Kingdom.
Plant Physiol. 2009 Jan;149(1):487-98. doi: 10.1104/pp.108.129411. Epub 2008 Oct 31.
The role of Delta4-unsaturated sphingolipid long-chain bases such as sphingosine was investigated in Arabidopsis (Arabidopsis thaliana). Identification and functional characterization of the sole Arabidopsis ortholog of the sphingolipid Delta4-desaturase was achieved by heterologous expression in Pichia pastoris. A P. pastoris mutant disrupted in the endogenous sphingolipid Delta4-desaturase gene was unable to synthesize glucosylceramides. Synthesis of glucosylceramides was restored by the expression of Arabidopsis gene At4g04930, and these sphingolipids were shown to contain Delta4-unsaturated long-chain bases, confirming that this open reading frame encodes the sphingolipid Delta4-desaturase. At4g04930 has a very restricted expression pattern, transcripts only being detected in pollen and floral tissues. Arabidopsis insertion mutants disrupted in the sphingolipid Delta4-desaturase At4g04930 were isolated and found to be phenotypically normal. Sphingolipidomic profiling of a T-DNA insertion mutant indicated the absence of Delta4-unsaturated sphingolipids in floral tissue, also resulting in the reduced accumulation of glucosylceramides. No difference in the response to drought or water loss was observed between wild-type plants and insertion mutants disrupted in the sphingolipid Delta4-desaturase At4g04930, nor was any difference observed in stomatal closure after treatment with abscisic acid. No differences in pollen viability between wild-type plants and insertion mutants were detected. Based on these observations, it seems unlikely that Delta4-unsaturated sphingolipids and their metabolites such as sphingosine-1-phosphate play a significant role in Arabidopsis growth and development. However, Delta4-unsaturated ceramides may play a previously unrecognized role in the channeling of substrates for the synthesis of glucosylceramides.
研究了如鞘氨醇等Δ4-不饱和鞘脂长链碱在拟南芥（Arabidopsis thaliana）中的作用。通过在巴斯德毕赤酵母中进行异源表达，实现了对鞘脂Δ4-去饱和酶唯一的拟南芥直系同源物的鉴定和功能表征。一个在内源鞘脂Δ4-去饱和酶基因中被破坏的巴斯德毕赤酵母突变体无法合成葡糖神经酰胺。拟南芥基因At4g04930的表达恢复了葡糖神经酰胺的合成，并且这些鞘脂被证明含有Δ4-不饱和长链碱，证实这个开放阅读框编码鞘脂Δ4-去饱和酶。At4g04930具有非常受限的表达模式，仅在花粉和花组织中检测到转录本。分离出在鞘脂Δ4-去饱和酶At4g04930中被破坏的拟南芥插入突变体，发现其表型正常。一个T-DNA插入突变体的鞘脂组学分析表明，花组织中不存在Δ4-不饱和鞘脂，这也导致葡糖神经酰胺的积累减少。在野生型植物和在鞘脂Δ4-去饱和酶At4g04930中被破坏的插入突变体之间，未观察到对干旱或水分流失反应的差异，在用脱落酸处理后气孔关闭方面也未观察到任何差异。未检测到野生型植物和插入突变体之间花粉活力的差异。基于这些观察结果，Δ4-不饱和鞘脂及其代谢物如鞘氨醇-1-磷酸似乎不太可能在拟南芥的生长和发育中发挥重要作用。然而，Δ4-不饱和神经酰胺可能在葡糖神经酰胺合成的底物通道化中发挥以前未被认识到的作用。
