Straying off the highway: Trafficking of secreted plant proteins and complexity in the plant cell wall proteome

摘要

From simply skimming through the abstract lists of more or less any collection of both basic and applied plant-related journals, it is immediately apparent that the plant cell wall represents a nexus of many fields of research: growth and development, plant-pathogen interactions, abiotic stress, self- and interorganismal recognition, signaling systems, numerous primary and specialized metabolic processes, biomaterials and bioproducts, and many others. That said, and to deal with an issue of semantics, while the term cell wall can refer specifically to the structural matrix that surrounds all plant cells, for the purposes of this Update it is used more broadly, also to include the apoplast, or extracellular environment. Given its multifunctional nature then, it is not surprising that the apoplast houses a dynamic and complex proteome, and the compendium of cell wall proteins continues to grow as researchers from disparate disciplines discover new roles for extracellular proteins. In addition, however, as cell wall proteomics projects develop and the subcellular localizations of an ever-growing list of plant proteins are determined, a number of surprises have been thrown up, both in terms of the identity of secreted proteins and the trafficking pathways that they follow. The purpose of this Update is to give some examples of previously unsuspected aspects of plant cell wall protein trafficking that are challenging longheld assumptions, rather than to provide an exhaustive review, and to highlight some questions that can be categorized into the "who, how, where, and when" of the cell wall proteome.