Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden.
Normandie Université, Laboratoire Glycobiologie et Matrice Extracellulaire Végétale (Glyco-MEV) EA 4358, Fédération de Recherche Normandie Végétal FED 4277, Université de Rouen, Rouen, France.
Ann Bot. 2021 May 7;127(6):709-713. doi: 10.1093/aob/mcab001.
Extensins are plant cell wall hydroxyproline-rich glycoproteins known to be involved in cell wall reinforcement in higher plants, and in defence against pathogen attacks. The ability of extensins to form intra- and intermolecular cross-links is directly related to their role in cell wall reinforcement. Formation of such cross-links requires appropriate glycosylation and structural conformation of the glycoprotein.
Although the role of cell wall components in plant defence has drawn increasing interest over recent years, relatively little focus has been dedicated to extensins. Nevertheless, new insights were recently provided regarding the structure and the role of extensins and their glycosylation in plant-microbe interactions, stimulating an interesting debate from fellow cell wall community experts. We have previously revealed a distinct distribution of extensin epitopes in Arabidopsis thaliana wild-type roots and in mutants impaired in extensin arabinosylation, in response to elicitation with flagellin 22. That study was recently debated in a Commentary by Tan and Mort (Tan L, Mort A. 2020. Extensins at the front line of plant defence. A commentary on: 'Extensin arabinosylation is involved in root response to elicitors and limits oomycete colonization'. Annals of Botany 125: vii-viii) and several points regarding our results were discussed. As a response, we herein clarify the points raised by Tan and Mort, and update the possible epitope structure recognized by the anti-extensin monoclonal antibodies. We also provide additional data showing differential distribution of LM1 extensin epitopes in roots between a mutant defective in PEROXIDASES 33 and 34 and the wild type, similarly to previous observations from the rra2 mutant defective in extensin arabinosylation. We propose these two peroxidases as potential candidates to specifically catalyse the cross-linking of extensins within the cell wall.
Extensins play a major role within the cell wall to ensure root protection. The cross-linking of extensins, which requires correct glycosylation and specific peroxidases, is most likely to result in modulation of cell wall architecture that allows enhanced protection of root cells against invading pathogens. Study of the relationship between extensin glycosylation and their cross-linking is a very promising approach to further understand how the cell wall influences root immunity.
伸展蛋白是富含羟脯氨酸的植物细胞壁糖蛋白，已知其参与高等植物细胞壁的加固以及对病原体攻击的防御。伸展蛋白形成分子内和分子间交联的能力与其在细胞壁加固中的作用直接相关。这种交联的形成需要糖蛋白的适当糖基化和结构构象。
尽管近年来植物细胞壁成分在植物防御中的作用引起了越来越多的关注，但相对较少关注伸展蛋白。然而，最近关于伸展蛋白的结构和功能及其在植物-微生物相互作用中的糖基化提供了新的见解，这激发了细胞壁社区专家的有趣辩论。我们之前揭示了在拟南芥野生型根中以及在伸展蛋白阿拉伯糖基化缺陷突变体中，在 flagellin 22 诱导下，伸展素表位的明显分布。该研究最近在 Tan 和 Mort 的评论中受到了辩论（Tan L, Mort A. 2020. Extensins at the front line of plant defence. A commentary on: 'Extensin arabinosylation is involved in root response to elicitors and limits oomycete colonization'. Annals of Botany 125: vii-viii），并讨论了我们研究结果的几个方面。作为回应，我们在此澄清了 Tan 和 Mort 提出的观点，并更新了识别抗伸展素单克隆抗体的可能表位结构。我们还提供了额外的数据，显示在 PEROXIDASES 33 和 34 缺陷型突变体和野生型之间，LM1 伸展素表位在根中的分布存在差异，这与之前 rra2 突变体中伸展素阿拉伯糖基化缺陷的观察结果相似。我们提出这两种过氧化物酶作为潜在的候选物，以特异性催化细胞壁内伸展素的交联。
伸展蛋白在细胞壁中起主要作用，以确保根的保护。伸展素的交联需要正确的糖基化和特定的过氧化物酶，这很可能导致细胞壁结构的调制，从而增强对根细胞免受入侵病原体的保护。研究伸展素糖基化与其交联之间的关系是进一步了解细胞壁如何影响根免疫的一个很有前途的方法。
