Comparative proteomics of cucurbit phloem indicates both unique and shared sets of proteins
Comparative proteomics of cucurbit phloem indicates both unique and shared sets of proteins
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DOI：
10.1111/tpj.13288
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发表时间：
2016-11-01
期刊：
影响因子：
7.2
通讯作者：
Turnbull, Colin G. N.
中科院分区：
文献类型：
--
作者：
Lopez-Cobollo, Rosa M.;Filippis, Ioannis;Turnbull, Colin G. N.
葫芦科植物是研究韧皮部生物学的重要模型，但在维管束内具有束状韧皮部(FP)，在束外韧皮部(EFP)也具有束状韧皮部。虽然这两个系统之间的功能差异尚不清楚，但糖类分析和有限的蛋白质图谱已经确定FP和EFP具有不同的组成。在这里，我们报道了南瓜和黄瓜两种葫芦科植物FP和EFP的详细比较蛋白质组学研究。我们通过视频显微镜重新检查了渗出物的部位，并证实在这两个物种中，组织切割后的自发渗出物几乎完全来自EFP。渗出物、筛分元件含量和显微解剖茎组织的比较凝胶电泳和基于质谱学的蛋白质组学证实，EFP和FP图谱高度不同，而且也存在物种差异。通过对葫芦科数据库的搜索，可以鉴定出每个物种的300多种FP蛋白。Fp和EFP的筛子元件含量之间几乎没有共享的蛋白质(约10%)，而且丰富的基因本体类别也不同。为了探索蛋白质组的数量差异，我们建立了黄瓜蛋白质的多种反应监测方法，这些蛋白质是FP或EFP的代表标记，并评估了组织切割后不同时间的渗出液成分。基于未能在渗出液样本中检测到FP标志物，我们得出结论，FP被非常迅速地阻止，因此对渗出液的贡献很小。总体而言，FP和EFP含量的高度差异表明它们基本上是独立的维管束。重要声明葫芦科是韧皮部模式植物，部分原因是汁液易于收集，但它们异常地同时具有维管束内的束状韧皮部(FP)和额外的束外韧皮部(EFP)，导致对渗出物来源的激烈辩论和对这两个系统之间潜在差异的不确定性。在这里，两个蛋白质组的比较显示几乎没有重叠，这不仅表明空间分离，而且表明功能分歧。
Cucurbits are well-studied models for phloem biology but unusually possess both fascicular phloem (FP) within vascular bundles and additional extrafascicular phloem (EFP). Although the functional differences between the two systems are not yet clear, sugar analysis and limited protein profiling have established that FP and EFP have divergent compositions. Here we report a detailed comparative proteomics study of FP and EFP in two cucurbits, pumpkin and cucumber. We re-examined the sites of exudation by video microscopy, and confirmed that in both species, the spontaneous exudate following tissue cutting derives almost exclusively from EFP. Comparative gel electrophoresis and mass spectrometry-based proteomics of exudates, sieve element contents and microdissected stem tissues established that EFP and FP profiles are highly dissimilar, and that there are also species differences. Searches against cucurbit databases enabled identification of more than 300 FP proteins from each species. Few of the detected proteins (about 10%) were shared between the sieve element contents of FP and EFP, and enriched Gene Ontology categories also differed. To explore quantitative differences in the proteomes, we developed multiple reaction monitoring methods for cucumber proteins that are representative markers for FP or EFP and assessed exudate composition at different times after tissue cutting. Based on failure to detect FP markers in exudate samples, we conclude that FP is blocked very rapidly and therefore makes a minimal contribution to the exudates. Overall, the highly divergent contents of FP and EFP indicate that they are substantially independent vascular compartments.Significance Statement Cucurbits are phloem model plants partly because sap exudate is easy to collect, but they unusually possess both fascicular phloem (FP) within vascular bundles and additional extrafascicular phloem (EFP), leading to hot debates on the origins of the exudate and uncertainty about the underlying differences between these two systems. Here, comparison of the two proteomes reveals little overlap, suggesting not only spatial separation but functional divergence.