Pirone-Davies Cary, Prior Natalie, von Aderkas Patrick, Smith Derek, Hardie Darryl, Friedman William E, Mathews Sarah
The Arnold Arboretum of Harvard University, Boston, MA, USA,
University of Victoria, Victoria, BC, Canada.
Ann Bot. 2016 May;117(6):973-84. doi: 10.1093/aob/mcw026. Epub 2016 Apr 4.
Many gymnosperms produce an ovular secretion, the pollination drop, during reproduction. The drops serve as a landing site for pollen, but also contain a suite of ions and organic compounds, including proteins, that suggests diverse roles for the drop during pollination. Proteins in the drops of species of Chamaecyparis, Juniperus, Taxus, Pseudotsuga, Ephedra and Welwitschia are thought to function in the conversion of sugars, defence against pathogens, and pollen growth and development. To better understand gymnosperm pollination biology, the pollination drop proteomes of pollination drops from two species of Cephalotaxus have been characterized and an ovular transcriptome for C. sinensis has been assembled.
Mass spectrometry was used to identify proteins in the pollination drops of Cephalotaxus sinensis and C. koreana RNA-sequencing (RNA-Seq) was employed to assemble a transcriptome and identify transcripts present in the ovules of C. sinensis at the time of pollination drop production.
About 30 proteins were detected in the pollination drops of both species. Many of these have been detected in the drops of other gymnosperms and probably function in defence, polysaccharide metabolism and pollen tube growth. Other proteins appear to be unique to Cephalotaxus, and their putative functions include starch and callose degradation, among others. Together, the proteins appear either to have been secreted into the drop or to occur there due to breakdown of ovular cells during drop production. Ovular transcripts represent a wide range of gene ontology categories, and some may be involved in drop formation, ovule development and pollen-ovule interactions.
The proteome of Cephalotaxus pollination drops shares a number of components with those of other conifers and gnetophytes, including proteins for defence such as chitinases and for carbohydrate modification such as β-galactosidase. Proteins likely to be of intracellular origin, however, form a larger component of drops from Cephalotaxus than expected from studies of other conifers. This is consistent with the observation of nucellar breakdown during drop formation in Cephalotaxus The transcriptome data provide a framework for understanding multiple metabolic processes that occur within the ovule and the pollination drop just before fertilization. They reveal the deep conservation of WUSCHEL expression in ovules and raise questions about whether any of the S-locus transcripts in Cephalotaxus ovules might be involved in pollen-ovule recognition.
许多裸子植物在繁殖过程中会产生一种胚珠分泌物——传粉滴。传粉滴是花粉的着陆点，但其还含有一系列离子和有机化合物，包括蛋白质，这表明传粉滴在授粉过程中具有多种作用。在扁柏属、刺柏属、红豆杉属、黄杉属、麻黄属和百岁兰属植物的传粉滴中的蛋白质，被认为在糖类转化、抵御病原体以及花粉生长和发育方面发挥作用。为了更好地理解裸子植物的授粉生物学，对两种三尖杉属植物传粉滴的蛋白质组进行了表征，并组装了中国粗榧的胚珠转录组。
使用质谱法鉴定中国粗榧和朝鲜粗榧传粉滴中的蛋白质。采用RNA测序（RNA-Seq）来组装转录组，并鉴定在传粉滴产生时中国粗榧胚珠中存在的转录本。
在这两个物种的传粉滴中检测到约30种蛋白质。其中许多在其他裸子植物的传粉滴中也被检测到，可能在防御、多糖代谢和花粉管生长中发挥作用。其他蛋白质似乎是三尖杉属特有的，其假定功能包括淀粉和胼胝质降解等。这些蛋白质似乎要么是被分泌到传粉滴中，要么是由于传粉滴产生过程中胚珠细胞的分解而出现在那里。胚珠转录本代表了广泛的基因本体类别，其中一些可能参与传粉滴形成、胚珠发育和花粉-胚珠相互作用。
三尖杉属传粉滴的蛋白质组与其他针叶树和买麻藤纲植物的蛋白质组有许多共同成分，包括防御蛋白如几丁质酶和碳水化合物修饰蛋白如β-半乳糖苷酶。然而，可能来自细胞内的蛋白质在三尖杉属传粉滴中所占比例比其他针叶树研究预期的要大。这与在三尖杉属传粉滴形成过程中珠心分解的观察结果一致。转录组数据为理解受精前胚珠和传粉滴内发生的多种代谢过程提供了一个框架。它们揭示了胚珠中WUSCHEL表达的深度保守性，并引发了关于三尖杉属胚珠中的任何S-位点转录本是否可能参与花粉-胚珠识别的问题。
