Department of Molecular Genetics, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, Germany.
Front Plant Sci. 2014 Mar 26;5:108. doi: 10.3389/fpls.2014.00108. eCollection 2014.
Endosperm transfer cells (ETCs) are positioned at the intersection of maternal and filial tissues in seeds of cereals and represent a bottleneck for apoplasmic transport of assimilates into the endosperm. Endosperm cellularization starts at the maternal-filial boundary and generates the highly specialized ETCs. During differentiation barley ETCs develop characteristic flange-like wall ingrowths to facilitate effective nutrient transfer. A comprehensive morphological analysis depicted distinct developmental time points in establishment of transfer cell (TC) morphology and revealed intracellular changes possibly associated with cell wall metabolism. Embedded inside the grain, ETCs are barely accessible by manual preparation. To get tissue-specific information about ETC specification and differentiation, laser microdissection (LM)-based methods were used for transcript and metabolite profiling. Transcriptome analysis of ETCs at different developmental stages by microarrays indicated activated gene expression programs related to control of cell proliferation and cell shape, cell wall and carbohydrate metabolism reflecting the morphological changes during early ETC development. Transporter genes reveal distinct expression patterns suggesting a switch from active to passive modes of nutrient uptake with the onset of grain filling. Tissue-specific RNA-seq of the differentiating ETC region from the syncytial stage until functionality in nutrient transfer identified a high number of novel transcripts putatively involved in ETC differentiation. An essential role for two-component signaling (TCS) pathways in ETC development of barley emerged from this analysis. Correlative data provide evidence for abscisic acid and ethylene influences on ETC differentiation and hint at a crosstalk between hormone signal transduction and TCS phosphorelays. Collectively, the data expose a comprehensive view on ETC development, associated pathways and identified candidate genes for ETC specification.
胚乳转移细胞（ETCs）位于禾本科种子中母体和胚胎组织的交汇处，是将同化产物质体运输到胚乳的瓶颈。胚乳细胞化始于母体-胚胎边界，并产生高度特化的 ETC。在分化过程中，大麦 ETC 会发展出特有的片状壁内突，以促进有效的养分转移。全面的形态分析描绘了建立转移细胞（TC）形态的不同发育时间点，并揭示了可能与细胞壁代谢相关的细胞内变化。ETC 嵌入在谷物内部，通过手动制备几乎无法获得组织特异性信息。为了获得关于 ETC 特化和分化的组织特异性信息，使用基于激光微切割（LM）的方法进行转录组和代谢物分析。通过微阵列对不同发育阶段的 ETC 进行转录组分析表明，与细胞增殖和细胞形状、细胞壁和碳水化合物代谢的控制相关的基因表达程序被激活，反映了早期 ETC 发育过程中的形态变化。转运蛋白基因显示出不同的表达模式，表明随着灌浆的开始，从主动吸收到被动吸收营养物质的模式发生了转变。从合胞体阶段到营养物质转移功能分化的 ETC 区域的组织特异性 RNA-seq 鉴定出了大量推测参与 ETC 分化的新转录本。来自该分析的一个重要发现是，双组分信号（TCS）途径在大麦 ETC 发育中的作用。相关数据为 ETC 分化中脱落酸和乙烯的影响提供了证据，并暗示激素信号转导和 TCS 磷酸传递之间存在串扰。总的来说，这些数据揭示了 ETC 发育、相关途径以及 ETC 特化的候选基因的全面视图。
