UMR INRAE 1158 BioEcoAgro, BIOPI Biologie des Plantes et Innovation, SFR Condorcet FR CNRS 3417, Université de Picardie, 33 Rue St Leu, 80039, Amiens, France.
Laboratoire Glycobiologie et Matrice Extracellulaire Végétale, Normandie Université, UNIROUEN, EA 4358, SFR 4377 NORVEGE, IRIB, Tremplin I2C Carnot, 76000, Rouen, France.
Plant J. 2020 Jul;103(2):617-633. doi: 10.1111/tpj.14753. Epub 2020 Apr 28.
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.
植物细胞壁的重塑在控制细胞伸长和分化方面起着关键作用。特别是，果胶甲酯化程度的精细调控被报道可以控制多种发育过程，如花粉萌发、花粉管伸长、原基的出现或暗生长下胚轴的伸长。然而，果胶的降解如何调节植物的发育仍然难以捉摸。在这里，我们报告了一个多聚半乳糖醛酸酶（PG）的特征，AtPGLR，其基因在拟南芥侧根出现时高度表达。由于基因补偿机制，突变体方法未能确定 AtPGLR 参与植物生长。为了克服这个问题，AtPGLR 已在酵母毕赤酵母中异源表达，并进行了生化特性分析。我们表明，AtPGLR 是一种内切 PG，在酸性 pH 下优先释放非甲酯化的低聚合度寡半乳糖醛酸（聚合度<8）。纯化的重组蛋白在百合花粉管上的应用，为研究酸性 pH 下的细胞壁重塑提供了一个极好的模型，导致花粉管异常或细胞质渗漏到花粉管尖端的亚顶域，在那里可以检测到非甲酯化的果胶表位。这些渗漏可以通过细胞壁中新的β-葡聚糖沉积（主要是几丁质）来修复，或者促进花粉管的剧烈爆裂。我们的工作展示了拟南芥 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。
