Soluble and Membrane-Bound β-Glucosidases Are Involved in Trimming the Xyloglucan Backbone
Soluble and Membrane-Bound β-Glucosidases Are Involved in Trimming the Xyloglucan Backbone
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DOI：
10.1104/pp.16.01713
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发表时间：
2017-02-01
期刊：
影响因子：
7.4
通讯作者：
Zarra, Ignacio
中科院分区：
文献类型：
--
作者：
Sampedro, Javier;Valdivia, Elene R.;Zarra, Ignacio
在许多开花植物中，木葡聚糖是初级细胞壁的主要组成部分，在生长调节中发挥着重要作用。木葡聚糖可以被一套能去除特定糖的外切糖苷酶降解。在这项工作中，我们发现由(1.4)连接的β-D-吡喃葡萄糖残基形成的木葡聚糖骨架可以被来自糖苷水解酶家族3的两种不同的拟南芥β-葡萄糖苷酶攻击。而BGLC1(At5g20950；对于木聚糖1的β-葡萄糖苷酶活性)负责所有或大部分的可溶性活性，而BGLC3(At5g04885)通常是一种膜锚定蛋白。这两个基因的突变，无论是它们自己的突变，还是与其他外切糖苷酶基因的突变相结合，都会导致部分消化的木聚糖亚单位的积累，如GXXG、GXLG或GXFG。虽然BGLC1的突变本身就有显著的影响，但缺乏BGLC3只会产生很小的影响。另一方面，双bglc1 bglc3突变体显示了协同作用，支持膜结合的bglc3在木聚糖代谢中的作用。此外，bglc1、bglc3还被BGLC1或BGLC3的过表达所补充。在高表达品系中，BGLC3活性集中在微生物体富集组分中，但也以可溶性形式存在。最后，这两个基因通常在相同的细胞类型中表达，尽管在某些情况下，BGLC3在比BGLC1更早的阶段表达。我们认为功能专门化可以解释这两种酶的单独定位，因为膜结合的b-葡萄糖苷酶可以特异性地消化可溶性的木葡聚糖，而不会影响壁结合的聚合物。
In many flowering plants, xyloglucan is a major component of primary cell walls, where it plays an important role in growth regulation. Xyloglucan can be degraded by a suite of exoglycosidases that remove specific sugars. In this work, we show that the xyloglucan backbone, formed by (1. 4)-linked beta-D-glucopyranosyl residues, can be attacked by two different Arabidopsis (Arabidopsis thaliana) beta-glucosidases from glycoside hydrolase family 3. While BGLC1 (At5g20950; for beta-glucosidase active against xyloglucan 1) is responsible for all or most of the soluble activity, BGLC3 (At5g04885) is usually a membraneanchored protein. Mutations in these two genes, whether on their own or combined with mutations in other exoglycosidase genes, resulted in the accumulation of partially digested xyloglucan subunits, such as GXXG, GXLG, or GXFG. While a mutation in BGLC1 had significant effects on its own, lack of BGLC3 had only minor effects. On the other hand, double bglc1 bglc3 mutants revealed a synergistic interaction that supports a role for membrane-bound BGLC3 in xyloglucan metabolism. In addition, bglc1 bglc3 was complemented by overexpression of either BGLC1 or BGLC3. In overexpression lines, BGLC3 activity was concentrated in a microsome-enriched fraction but also was present in soluble form. Finally, both genes were generally expressed in the same cell types, although, in some cases, BGLC3 was expressed at earlier stages than BGLC1. We propose that functional specialization could explain the separate localization of both enzymes, as a membrane-bound b-glucosidase could specifically digest soluble xyloglucan without affecting the wall-bound polymer.