Yang Ning, Wang Tai
Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, and National Center for Plant Gene Research, 20 Nanxincun, Xiangshan, Haidianqu, Beijing, 100093, China.
BMC Plant Biol. 2017 Jan 5;17(1):2. doi: 10.1186/s12870-016-0961-7.
The coordination of pollen tube (PT) growth, guidance and timely growth arrest and rupture mediated by PT-pistil interaction is crucial for the PT to transport sperm cells into ovules for double fertilization. The plasma membrane (PM) represents an important interface for cell-cell interaction, and PM proteins of PTs are pioneers for mediating PT integrity and interaction with pistils. Thus, understanding the mechanisms underlying these events is important for proteomics.
Using the efficient aqueous polymer two-phase system and alkali buffer treatment, we prepared high-purity PM from mature and germinated pollen of rice. We used iTRAQ quantitative proteomic methods and identified 1,121 PM-related proteins (PMrPs) (matched to 899 loci); 192 showed differential expression in the two pollen cell types, 119 increased and 73 decreased in abundance during germination. The PMrP and differentially expressed PMrP sets all showed a functional skew toward signal transduction, transporters, wall remodeling/metabolism and membrane trafficking. Their genomic loci had strong chromosome bias. We found 37 receptor-like kinases (RLKs) from 8 kinase subfamilies and 209 transporters involved in flux of diversified ions and metabolites. In combination with the rice pollen transcriptome data, we revealed that in general, the protein expression of these PMrPs disagreed with their mRNA expression, with inconsistent mRNA expression for 74% of differentially expressed PMrPs.
This study identified genome-wide pollen PMrPs, and provided insights into the membrane profile of receptor-like kinases and transporters important for pollen tube growth and interaction with pistils. These pollen PMrPs and their mRNAs showed discordant expression. This work provides resource and knowledge to further dissect mechanisms by which pollen or the PT controls PMrP abundance and monitors interactions and ion and metabolite exchanges with female cells in rice.
花粉管（PT）生长、导向以及由PT与雌蕊相互作用介导的适时生长停滞和破裂的协调，对于PT将精细胞运输到胚珠中进行双受精至关重要。质膜（PM）是细胞间相互作用的重要界面，PT的PM蛋白是介导PT完整性以及与雌蕊相互作用的先驱。因此，了解这些事件背后的机制对于蛋白质组学很重要。
利用高效的水相聚合物双相系统和碱性缓冲液处理，我们从水稻成熟花粉和萌发花粉中制备了高纯度的PM。我们使用iTRAQ定量蛋白质组学方法，鉴定了1121种与PM相关的蛋白质（PMrP）（匹配到899个基因座）；192种在两种花粉细胞类型中表现出差异表达，萌发过程中有119种丰度增加，73种丰度降低。PMrP集和差异表达的PMrP集在功能上均偏向信号转导、转运蛋白、细胞壁重塑/代谢和膜运输。它们的基因组位点具有很强的染色体偏向性。我们从8个激酶亚家族中发现了37种类受体激酶（RLK）和209种参与多种离子和代谢物通量的转运蛋白。结合水稻花粉转录组数据，我们发现，总体而言，这些PMrP的蛋白质表达与其mRNA表达不一致，74%的差异表达PMrP的mRNA表达不一致。
本研究鉴定了全基因组范围的花粉PMrP，并深入了解了对花粉管生长以及与雌蕊相互作用很重要的类受体激酶和转运蛋白的膜概况。这些花粉PMrP及其mRNA表现出不一致的表达。这项工作为进一步剖析花粉或花粉管控制PMrP丰度以及监测与水稻雌细胞相互作用和离子及代谢物交换的机制提供了资源和知识。
