Group III-A XTH Genes of Arabidopsis Encode Predominant Xyloglucan Endohydrolases That Are Dispensable for Normal Growth
Group III-A XTH Genes of Arabidopsis Encode Predominant Xyloglucan Endohydrolases That Are Dispensable for Normal Growth
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DOI：
10.1104/pp.112.207308
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发表时间：
2013-01-01
期刊：
影响因子：
7.4
通讯作者：
Brumer, Harry
中科院分区：
文献类型：
--
作者：
Kaewthai, Nomchit;Gendre, Delphine;Brumer, Harry
初生壁延伸的分子基础一直是植物细胞形态发生的中心谜团之一。经典的细胞壁模型表明，木葡聚糖内切-转糖基酶活性是通过木葡聚糖-纤维素交联链的瞬时断裂和宗教化来控制细胞壁松动的主要催化剂(与扩展蛋白一起)。拟南芥基因组包含33个系统发育不同的木葡聚糖内切酶/水解酶(Xth)基因产物，其中两个被预测为主要的木葡聚糖内水解酶，因为聚为III-A组。对重组AtXTH31的酶动力学分析证实了这一预测，并表明该酶具有与玉米草(Tropaeolum Majus)木葡聚糖酶1相似的催化特性，该酶负责在萌发过程中储存木葡聚糖的水解酶。对Genevestigator数据的全球分析表明，AtXTH31和邻近的AtXTH32在扩张的组织中大量表达。显微镜分析表明，木葡聚糖寡糖XXXG的间苯二酚β-糖苷作为原位探针，在根和下胚轴的特定区域都有明显的木葡聚糖内水解酶活性，这与转录数据具有很好的相关性。此外，在AtXTH31/AtXTH32双基因敲除系中，这种水解性基本上被完全消除。然而，AtXTH31和AtXTH32的单、双基因敲除品系以及单独的高表达品系没有表现出显著的生长发育表型。这些结果表明，尽管木聚糖多糖的水解与初生壁的扩张是平行发生的，但形态效应是微妙的，或者可能被其他机制补偿。我们推测，在基质木聚糖的水解性修饰中，这些木葡聚糖内水解酶和最近发现的质外体外糖苷酶之间可能存在相互作用。
The molecular basis of primary wall extension endures as one of the central enigmas in plant cell morphogenesis. Classical cell wall models suggest that xyloglucan endo-transglycosylase activity is the primary catalyst (together with expansins) of controlled cell wall loosening through the transient cleavage and religation of xyloglucan-cellulose cross links. The genome of Arabidopsis (Arabidopsis thaliana) contains 33 phylogenetically diverse XYLOGLUCAN ENDO-TRANSGLYCOSYLASE/HYDROLASE (XTH) gene products, two of which were predicted to be predominant xyloglucan endohydrolases due to clustering into group III-A. Enzyme kinetic analysis of recombinant AtXTH31 confirmed this prediction and indicated that this enzyme had similar catalytic properties to the nasturtium (Tropaeolum majus) xyloglucanase1 responsible for storage xyloglucan hydrolysis during germination. Global analysis of Genevestigator data indicated that AtXTH31 and the paralogous AtXTH32 were abundantly expressed in expanding tissues. Microscopy analysis, utilizing the resorufin beta-glycoside of the xyloglucan oligosaccharide XXXG as an in situ probe, indicated significant xyloglucan endohydrolase activity in specific regions of both roots and hypocotyls, in good correlation with transcriptomic data. Moreover, this hydrolytic activity was essentially completely eliminated in AtXTH31/AtXTH32 double knockout lines. However, single and double knockout lines, as well as individual overexpressing lines, of AtXTH31 and AtXTH32 did not demonstrate significant growth or developmental phenotypes. These results suggest that although xyloglucan polysaccharide hydrolysis occurs in parallel with primary wall expansion, morphological effects are subtle or may be compensated by other mechanisms. We hypothesize that there is likely to be an interplay between these xyloglucan endohydrolases and recently discovered apoplastic exo-glycosidases in the hydrolytic modification of matrix xyloglucans.