Making and breaking of boron bridges in the pectic domain rhamnogalacturonan-II at apoplastic pH in vivo and in vitro
Making and breaking of boron bridges in the pectic domain rhamnogalacturonan-II at apoplastic pH in vivo and in vitro
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DOI：
10.1111/tpj.16112
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发表时间：
2023-02-08
期刊：
影响因子：
7.2
通讯作者：
Fry，Stephen C.
中科院分区：
文献类型：
--
作者：
Begum，Rifat Ara;Messenger，David J.;Fry，Stephen C.
细胞壁果胶结构域鼠李半乳糖醛酸聚糖-II（RG-II）通过芹菜糖残基之间的硼桥交联对于正常植物生长和发育是必不可少的，但对其机制或可逆性知之甚少。我们表征了体内和体外“质外体”pH下硼桥的形成和断裂。RG-II（13-26 μm）在含有和不含1.2 mmH 3BO 3和阳离子伴侣（Ca 2+、Pb 2+、多聚组氨酸或阿拉伯半乳聚糖蛋白寡肽）的活Rosacell培养物和无细胞培养基中孵育。对RG‐II的交联状态进行了放射学监测。二聚体RG‐II在体内和体外pH 2.0- 7.0下稳定。体外二聚化在所有测试pH（1.75-7.0）下都需要“催化”阳离子;因此，仅中和RG‐II的负电荷（pH 1.75）并不能实现硼桥接。Pb 2+（20-2500 μm）在pH1.75 -4.0范围内有很强的抑制作用，但在pH4.75 -7.0范围内不起作用。阳离子肽在约1-30 μm时有效;较高的浓度导致较少的二聚化，可能是因为两个RG-II很少与同一肽分子结合。肽在pH 1.75时无效，其最适pH为2.5- 4.75。d-芹菜糖（>40 mm）在体外阻断RG-II二聚化，但不裂解现有的硼桥。Rosacells不摄取upd-[U-14 C]芹菜糖;因此，外源性芹菜糖在体内仅阻断质外体RG-II二聚化。总之，质外体pH既不打破硼桥，也不阻止其形成。因此，硼饥饿的细胞不能从RG-II中回收硼，并且RG-II的pH依赖性单体化不能实现“酸生长”。二价金属和阳离子肽分别通过配位键和离子键催化RG-II二聚化（在pH 1.75下分别为可能和不可能）。外源芹菜糖可能有助于区分原生质内和原生质外二聚化。
Cross‐linking of the cell‐wall pectin domain rhamnogalacturonan‐II (RG‐II) via boron bridges between apiose residues is essential for normal plant growth and development, but little is known about its mechanism or reversibility. We characterized the making and breaking of boron bridgesin vivoandin vitroat ‘apoplastic’ pH. RG‐II (13–26 μm) was incubated in livingRosacell cultures and cell‐free media with and without 1.2 mmH3BO3and cationic chaperones (Ca2+, Pb2+, polyhistidine, or arabinogalactan‐protein oligopeptides). The cross‐linking status of RG‐II was monitored electrophoretically. Dimeric RG‐II was stable at pH 2.0–7.0in vivoandin vitro.In‐vitrodimerization required a ‘catalytic’ cation at all pHs tested (1.75–7.0); thus, merely neutralizing the negative charge of RG‐II (at pH 1.75) does not enable boron bridging. Pb2+(20–2500 μm) was highly effective at pH 1.75–4.0, but not 4.75–7.0. Cationic peptides were effective at approximately 1–30 μm; higher concentrations caused less dimerization, probably because two RG‐IIs then rarely bonded to the same peptide molecule. Peptides were ineffective at pH 1.75, their pH optimum being 2.5–4.75.d‐Apiose (>40 mm) blocked RG‐II dimerizationin vitro, but did not cleave existing boron bridges.Rosacells did not take upd‐[U‐14C]apiose; therefore, exogenous apiose would block onlyapoplasticRG‐II dimerizationin vivo. In conclusion, apoplastic pH neither broke boron bridges nor prevented their formation. Thus boron‐starved cells cannot salvage boron from RG‐II, and ‘acid growth’ is not achieved by pH‐dependent monomerization of RG‐II. Divalent metals and cationic peptides catalyse RG‐II dimerization via co‐ordinate and ionic bonding respectively (possible and impossible, respectively, at pH 1.75). Exogenous apiose may be useful to distinguish intra‐ and extra‐protoplasmic dimerization.