Function of xyloglucan endotransglucosylase/hydrolases in rice
Function of xyloglucan endotransglucosylase/hydrolases in rice
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DOI：
10.1093/aob/mct292
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发表时间：
2014-10-01
期刊：
影响因子：
4.2
通讯作者：
Nishitani, Kazuhiko
中科院分区：
文献类型：
--
作者：
Hara, Yoshinao;Yokoyama, Ryusuke;Nishitani, Kazuhiko
背景和目的虽然木葡聚糖普遍存在于陆地植物中，但它们在禾本科物种中的含量低于真双子叶植物。禾本科植物细胞壁含有比木葡聚糖更高水平的β-1，3/1，4混合连接葡聚糖和阿拉伯聚糖。尽管禾本科植物中的木葡聚糖水平相对较低，但水稻（Oryza sativa）中的木葡聚糖内切转葡糖基酶/水解酶（XTH）基因家族在大小上与真双子叶植物拟南芥（Arabidopsis thaliana）相当。这就提出了一个问题，即木葡聚糖是否是水稻XTH基因产物的底物，其酶活性在很大程度上尚未表征。（其属于XTH家族的第IIIA组，并且在水稻幼苗的生长组织中特异性表达），以及另外两个XTH，OsXTH 11（I/II组）和OsXTH 20（第IIIA组）作为参考，并对三种重组水稻XTH，即OsXTH 11，OsXTH 20和OsXTH 19。关键结果OsXTH基因的三个产物均具有木葡聚糖内切水解酶（XEH，EC 3.2.1.151）活性，OsXTH 11同时具有XEH和木葡聚糖内糖基转移酶（XET，EC 2.4.1207）活性。然而，这些蛋白质既没有水解酶，也没有转葡糖基酶活性时，glucuronoarabinoxylan或混合键葡聚糖用作底物。这些结果与组织学观察结果一致，表明pOsXTH 19：：GUS在存在木葡聚糖免疫反应性的组织附近特异性表达。过量表达OsXTH 19（携带花椰菜花叶病毒35 S启动子：：OsXTH 19 cDNA构建体）或具有抑制OsXTH 19表达（携带pOsXTH 19 RNAi构建体）的转基因水稻品系没有显示出显著的表型变化，表明XTH家族成员之间的功能冗余和协作，如在A.结论OsXTH 20和OsXTH 19仅对木葡聚糖具有水解酶活性，而OsXTH 11仅对木葡聚糖具有水解酶和XET活性。对OsXTH 19表达改变的转基因株系的表型分析表明，OsXTH 19和相关的XTH在水稻生长中起着冗余的作用。
Background and Aims Although xyloglucans are ubiquitous in land plants, they are less abundant in Poales species than in eudicotyledons. Poales cell walls contain higher levels of beta-1,3/1,4 mixed-linked glucans and arabinoxylans than xyloglucans. Despite the relatively low level of xyloglucans in Poales, the xyloglucan endotransglucosylase/hydrolase (XTH) gene family in rice (Oryza sativa) is comparable in size to that of the eudicotyledon Arabidopsis thaliana. This raises the question of whether xyloglucan is a substrate for rice XTH gene products, whose enzyme activity remains largely uncharacterized.Methods This study focused on OsXTH19 (which belongs to Group IIIA of the XTH family and is specifically expressed in growing tissues of rice shoots), and two other XTHs, OsXTH11 (Group I/II) and OsXTH20 (Group IIIA), for reference, and measurements were made of the enzymatic activities of three recombinant rice XTHs, i.e. OsXTH11, OsXTH20 and OsXTH19.Key Results All three OsXTH gene products have xyloglucan endohydrolase (XEH, EC 3.2.1.151) activity, and OsXTH11 has both XEH and xyloglucan endotransglycosylase (XET, EC 2.4.1207) activities. However, these proteins had neither hydrolase nor transglucosylase activity when glucuronoarabinoxylan or mixed-linkage glucan was used as the substrate. These results are consistent with histological observations demonstrating that pOsXTH19::GUS is expressed specifically in the vicinity of tissues where xyloglucan immunoreactivity is present. Transgenic rice lines over-expressing OsXTH19 (harbouring a Cauliflower Mosaic Virus 35S promoter:: OsXTH19 cDNA construct) or with suppressed OsXTH19 expression (harbouring a pOsXTH19 RNAi construct) did not show dramatic phenotypic changes, suggesting functional redundancy and collaboration among XTH family members, as was observed in A. thaliana.Conclusions OsXTH20 and OsXTH19 act as hydrolases exclusively on xyloglucan, while OsXTH11 exhibits both hydrolase and XET activities exclusively on xyloglucans. Phenotypic analysis of transgenic lines with altered expression of OsXTH19 suggests that OsXTH19 and related XTH(s) play redundant roles in rice growth.