Plant cell wall remodeling plays a key role in the control of cell elongation and differentiation. In particular, fine‐tuning of the degree of methylesterification of pectins was previously reported to control developmental processes as diverse as pollen germination, pollen tube elongation, emergence of primordia or elongation of dark‐grown hypocotyls. However, how pectin degradation can modulate plant development has remained elusive. Here we report the characterization of a polygalacturonase (PG), AtPGLR, the gene for which is highly expressed at the onset of lateral root emergence in Arabidopsis. Due to gene compensation mechanisms, mutant approaches failed to determine the involvement of AtPGLR in plant growth. To overcome this issue, AtPGLR has been expressed heterologously in the yeast Pichia pastoris and biochemically characterized. We showed that AtPGLR is an endo‐PG that preferentially releases non‐methylesterified oligogalacturonides with a short degree of polymerization (< 8) at acidic pH. The application of the purified recombinant protein on Amaryllis pollen tubes, an excellent model for studying cell wall remodeling at acidic pH, induced abnormal pollen tubes or cytoplasmic leakage in the subapical dome of the pollen tube tip, where non‐methylesterified pectin epitopes are detected. Those leaks could either be repaired by new β‐glucan deposits (mostly callose) in the cell wall or promoted dramatic burst of the pollen tube. Our work presents the full biochemical characterization of an Arabidopsis PG and highlights the importance of pectin integrity in pollen tube elongation.

中文翻译：

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AtPGLR（一种内聚半乳糖醛酸酶）的外源应用会触发花粉管破裂和修复。

植物细胞壁重塑在控制细胞伸长和分化中起关键作用。特别是，据报道，微调果胶的甲基化程度可控制各种发育过程，如花粉萌发，花粉管伸长，原基出现或暗长的下胚轴伸长。然而，果胶降解如何调节植物发育仍不清楚。在这里，我们报道了一个聚半乳糖醛酸酶（PG），AtPGLR的表征，该基因在拟南芥侧根出苗开始时就高度表达。由于基因补偿机制，突变方法无法确定AtPGLR是否参与植物生长。为了克服这个问题，AtPGLR已在酵母中异源表达巴斯德毕赤酵母和生化特性。我们发现，AtPGLR是一种内切-PG优先释放与在酸性pH下聚合（<8）的短程度的非甲基酯化oligogalacturonides。纯化的重组蛋白在孤挺花上的应用花粉管是研究酸性pH下细胞壁重塑，诱导异常的花粉管或在花粉管尖端的根尖下圆顶中细胞质泄漏的极好模型，其中检测到未甲基酯化的果胶表位。这些泄漏可以通过细胞壁中新的β-葡聚糖沉积物（主要是call）来修复，或者可以促进花粉管的急剧破裂。我们的工作提出了拟南芥PG的完整生化特征，并强调了果胶完整性在花粉管伸长中的重要性。