Wasąg Piotr, Suwińska Anna, Zakrzewski Przemysław, Walczewski Jakub, Lenartowski Robert, Lenartowska Marta
Laboratory of Isotope and Instrumental Analysis, Faculty of Biology and Environmental Protection, Nicolaus Copernicus University in Toruń, Toruń, Poland.
Laboratory of Developmental Biology, Faculty of Biology and Environmental Protection, Nicolaus Copernicus University in Toruń, Toruń, Poland.
Protoplasma. 2018 Jan;255(1):57-67. doi: 10.1007/s00709-017-1134-8. Epub 2017 Jun 15.
Calcium (Ca) plays essential roles in generative reproduction of angiosperms, but the sites and mechanisms of Ca storage and mobilization during pollen-pistil interactions have not been fully defined. Both external and internal Ca stores are likely important during male gametophyte communication with the sporophytic and gametophytic cells within the pistil. Given that calreticulin (CRT), a Ca-buffering protein, is able to bind Ca reversibly, it can serve as a mobile store of easily releasable Ca (so called an exchangeable Ca) in eukaryotic cells. CRT has typical endoplasmic reticulum (ER) targeting and retention signals and resides primarily in the ER. However, localization of this protein outside the ER has also been revealed in both animal and plant cells, including Golgi/dictyosomes, nucleus, plasma membrane/cell surface, plasmodesmata, and even extracellular matrix. These findings indicate that CRT may function in a variety of different cell compartments and specialized structures. We have recently shown that CRT is highly expressed and accumulated in the ER of plant cells involved in pollen-pistil interactions in Petunia, and we proposed an essential role for CRT in intracellular Ca storage and mobilization during the key reproductive events. Here, we demonstrate that both CRT and exchangeable Ca are localized in the intra/extracellular peripheries of highly specialized plant cells, such as the pistil transmitting tract cells, pollen tubes, nucellus cells surrounding the embryo sac, and synergids. Based on our present results, we propose that extracellularly located CRT is also involved in Ca storage and mobilization during sexual reproduction of angiosperms.
钙（Ca）在被子植物的有性生殖中起着至关重要的作用，但在花粉与雌蕊相互作用过程中钙储存和动员的位点及机制尚未完全明确。在雄配子体与雌蕊内的孢子体细胞和配子体细胞进行交流时，细胞外和细胞内的钙库可能都很重要。鉴于钙网蛋白（CRT）是一种钙缓冲蛋白，能够可逆地结合钙，它可以作为真核细胞中易于释放的钙（即所谓的可交换钙）的移动储存库。CRT具有典型的内质网（ER）靶向和保留信号，主要位于内质网中。然而，在动物和植物细胞中也发现了该蛋白在内质网之外的定位，包括高尔基体/ 液泡、细胞核、质膜/细胞表面、胞间连丝，甚至细胞外基质。这些发现表明CRT可能在多种不同的细胞区室和特殊结构中发挥作用。我们最近发现，在矮牵牛中参与花粉与雌蕊相互作用的植物细胞内质网中，CRT高度表达并积累，我们提出CRT在关键生殖事件期间的细胞内钙储存和动员中起着重要作用。在这里，我们证明CRT和可交换钙都定位在高度特化的植物细胞的细胞内/外周边区域，如雌蕊传递组织细胞、花粉管、围绕胚囊的珠心细胞和助细胞。基于我们目前的结果，我们提出细胞外定位的CRT也参与被子植物有性生殖过程中的钙储存和动员。
