Chen Kuo-En, Karinshak Marilee, Vierstra Richard D
Department of Biology Washington University in St. Louis St. Louis Missouri USA.
Plant Direct. 2025 Jul 2;9(7):e70087. doi: 10.1002/pld3.70087. eCollection 2025 Jul.
The apoplastic space surrounding plant cells, encompassing the cell wall matrix, extracellular spaces, and xylem, is one of the least understood compartments within plant tissues due to its lack of limiting membranes and its unavoidable damage upon tissue homogenization. Using a streamlined vacuum-infiltration/centrifugation protocol to enrich for the apoplastic fluid (APF) combined with in-depth tandem mass spectrometry, we provide an improved view of its proteome that includes over 1500 proteins possibly assigned to this compartment with minimized cytosolic contamination. Included are large and varied collections of polypeptides associated with cell wall metabolism, oxido-reductase reactions, cell-cell signaling, proteolysis, and pathogen protection via basal defense pathways. While numerous apoplast proteins were predicted to house N-terminal signal peptide sequences that direct extracellular secretion, many did not, suggesting widespread use of non-classical export route(s). Among APF constituents are numerous pathogenesis-related proteins, glycosidases, aspartyl and subtilisin-type serine proteases, and the complement of subunits that assemble the core particle of the 26S proteasome. When this APF proteome is compared with those based on two prior isolation methods, a consensus collection of 338 polypeptides emerges that offers a comprehensive view of the core APF proteome that manages the cell wall and interfaces with the environment.
植物细胞周围的质外体空间，包括细胞壁基质、细胞外空间和木质部，由于其缺乏限制膜且在组织匀浆时不可避免地受到损伤，是植物组织中最不为人所了解的区室之一。我们采用简化的真空渗透/离心方案来富集质外体流体（APF），并结合深度串联质谱分析，从而对其蛋白质组有了更深入的认识，其中包括1500多种可能定位于该区室且胞质污染最小的蛋白质。这些蛋白质包括与细胞壁代谢、氧化还原酶反应、细胞间信号传导、蛋白水解以及通过基础防御途径进行病原体保护相关的大量且多样的多肽集合。虽然许多质外体蛋白预计含有指导细胞外分泌的N端信号肽序列，但也有许多蛋白没有，这表明非经典分泌途径被广泛使用。APF的成分包括许多病程相关蛋白、糖苷酶、天冬氨酸和枯草杆菌蛋白酶型丝氨酸蛋白酶，以及组装26S蛋白酶体核心颗粒的亚基组成。当将这个APF蛋白质组与基于之前两种分离方法的蛋白质组进行比较时，出现了一个由338种多肽组成的共识集合，它提供了一个管理细胞壁并与环境相互作用的核心APF蛋白质组的全面视图。
