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A Group of O-Acetyltransferases Catalyze Xyloglucan Backbone Acetylation and Can Alter Xyloglucan Xylosylation Pattern and Plant Growth When Expressed in Arabidopsis.
Plant & Cell Physiology ( IF 4.9 ) Pub Date : 2020-03-13 , DOI: 10.1093/pcp/pcaa031
Ruiqin Zhong 1 , Dongtao Cui 2 , Dennis R Phillips 3 , Elizabeth A Richardson 4 , Zheng-Hua Ye 1
Affiliation  

Xyloglucan is a major hemicellulose in plant cell walls and exists in two distinct types, XXXG and XXGG. While the XXXG-type xyloglucan from dicot species only contains O-acetyl groups on side-chain galactose (Gal) residues, the XXGG-type xyloglucan from Poaceae (grasses) and Solanaceae bears O-acetyl groups on backbone glucosyl (Glc) residues. Although O-acetyltransferases responsible for xyloglucan Gal acetylation have been characterized, the biochemical mechanism underlying xyloglucan backbone acetylation remains to be elucidated. In this study, we showed that recombinant proteins of a group of DUF231 members from rice and tomato were capable of transferring acetyl groups onto O-6 of Glc residues in cello-oligomer acceptors, indicating that they are xyloglucan backbone 6-O-acetyltransferases (XyBATs). We further demonstrated that XyBAT-acetylated cellohexaose oligomers could be readily xylosylated by AtXXT1 (Arabidopsis xyloglucan xylosyltransferase 1) to generate acetylated, xylosylated cello-oligomers, whereas AtXXT1-xylosylated cellohexaose oligomers were much less effectively acetylated by XyBATs. Heterologous expression of a rice XyBAT in Arabidopsis led to a severe reduction in cell expansion and plant growth and a drastic alteration in xyloglucan xylosylation pattern with the formation of acetylated XXGG-type units, including XGG, XGGG, XXGG, XXGG,XXGGG and XXGGG (G denotes acetylated Glc). In addition, recombinant proteins of two Arabidopsis XyBAT homologs also exhibited O-acetyltransferase activity toward cellohexaose, suggesting their possible role in mediating xyloglucan backbone acetylation in vivo. Our findings provide new insights into the biochemical mechanism underlying xyloglucan backbone acetylation and indicate the importance of maintaining the regular xyloglucan xylosylation pattern in cell wall function.

中文翻译:

一组O-乙酰基转移酶催化木葡聚糖主链乙酰化并可以改变木葡聚糖木糖基化模式和植物生长时在拟南芥中表达。

木葡聚糖是植物细胞壁中的主要半纤维素,并且以两种不同的类型存在,即XXXG和XXGG。来自双子叶植物的XXXG型木葡聚糖仅在侧链半乳糖(Gal)残基上包含O-乙酰基,而来自禾本科(禾本科)和茄科的XXGG型木葡聚糖在主链葡萄糖基(Glc)残基上带有O-乙酰基。尽管已经表征了负责木葡聚糖Gal乙酰化的O-乙酰基转移酶,但仍需要阐明木葡聚糖主链乙酰化的基础生化机制。在这项研究中,我们显示了水稻和番茄中一组DUF231成员的重组蛋白能够将乙酰基转移到O纤维低聚物受体中Glc残基的-6,表明它们是木葡聚糖主链6- O-乙酰基转移酶(XyBATs)。我们进一步证明了XyBAT乙酰化纤维六糖低聚物可以很容易地被AtXXT1(拟南芥木糖葡聚糖木糖基转移酶1)木糖基化以生成乙酰化的木糖基化纤维低聚物,而AtXXT1-木糖基化纤维六糖低聚物被XyBAT乙酰化的效率要低得多。水稻XyBAT在拟南芥中的异源表达导致细胞扩增和植物生长严重降低,木葡聚糖木糖基化模式发生剧烈变化,并形成乙酰化XXGG型单元,包括X G G,X GG G,XX G G, XX GG,XX GGG和XX GG G(G表示乙酰化的Glc)。此外,两个拟南芥XyBAT同源物的重组蛋白还表现出对纤维己糖的O-乙酰基转移酶活性,表明它们可能在体内介导木葡聚糖主链乙酰化中发挥作用。我们的发现为木葡聚糖主链乙酰化的生化机制提供了新的见解,并指出了维持细胞壁功能中常规木葡聚糖木糖基化模式的重要性。
更新日期:2020-03-13
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