Protecting Crops and the Environment, Rothamsted Research, Hertfordshire, AL5 2JQ, U.K.
NIAB, 93 Lawrence Weaver Road, Cambridge, CB3 0LE, U.K.
Essays Biochem. 2022 Sep 30;66(5):595-605. doi: 10.1042/EBC20220159.
The apoplast comprises the intercellular space between cell membranes, includes the xylem, and extends to the rhizoplane and the outer surfaces of the plant. The apoplast plays roles in different biological processes including plant immunity. This highly specialised space is often the first place where pathogen recognition occurs, and this then triggers the immune response. The immune response in the apoplast involves different mechanisms that restrict pathogen infection. Among these responses, secretion of different molecules like proteases, proteins related to immunity, small RNAs and secondary metabolites play important and often additive or synergistic roles. In addition, production of reactive oxygen species occurs to cause direct deleterious effects on the pathogen as well as reinforce the plant's immune response by triggering modifications to cell wall composition and providing additional defence signalling capabilities. The pool of available sugar in the apoplast also plays a role in immunity. These sugars can be manipulated by both interactors, pathogens gaining access to nutrients whilst the plant's responses restrict the pathogen's access to nutrients. In this review, we describe the latest findings in the field to highlight the importance of the apoplast in plant-pathogen interactions and plant immunity. We also indicate where new discoveries are needed.
质外体包括细胞膜之间的细胞间隙，包括木质部，并延伸到根际和植物的外表面。质外体在包括植物免疫在内的不同生物学过程中发挥作用。这个高度专门化的空间通常是病原体识别发生的第一地点，然后触发免疫反应。质外体中的免疫反应涉及限制病原体感染的不同机制。在这些反应中，不同分子的分泌，如蛋白酶、与免疫相关的蛋白质、小 RNA 和次生代谢物，发挥着重要作用，并且通常具有加性或协同作用。此外，活性氧的产生会对病原体造成直接的有害影响，并通过触发细胞壁成分的修饰和提供额外的防御信号能力来增强植物的免疫反应。质外体中可用糖的池也在免疫中发挥作用。这些糖可以被相互作用者操纵，病原体获得营养，而植物的反应限制了病原体获得营养的机会。在这篇综述中，我们描述了该领域的最新发现，以强调质外体在植物-病原体相互作用和植物免疫中的重要性。我们还指出了需要新发现的地方。
