Van Sandt Vicky S T, Stieperaere Herman, Guisez Yves, Verbelen Jean-Pierre, Vissenberg Kris
Plant Physiology and Morphology, Department of Biology, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
Ann Bot. 2007 Jan;99(1):39-51. doi: 10.1093/aob/mcl232. Epub 2006 Nov 10.
In angiosperms xyloglucan endotransglucosylase (XET)/hydrolase (XTH) is involved in reorganization of the cell wall during growth and development. The location of oligo-xyloglucan transglucosylation activity and the presence of XTH expressed sequence tags (ESTs) in the earliest diverging extant plants, i.e. in bryophytes and algae, down to the Phaeophyta was examined. The results provide information on the presence of an XET growth mechanism in bryophytes and algae and contribute to the understanding of the evolution of cell wall elongation in general.
Representatives of the different plant lineages were pressed onto an XET test paper and assayed. XET or XET-related activity was visualized as the incorporation of fluorescent signal. The Physcomitrella genome database was screened for the presence of XTHs. In addition, using the 3' RACE technique searches were made for the presence of possible XTH ESTs in the Charophyta.
XET activity was found in the three major divisions of bryophytes at sites corresponding to growing regions. In the Physcomitrella genome two putative XTH-encoding cDNA sequences were identified that contain all domains crucial for XET activity. Furthermore, XET activity was located at the sites of growth in Chara (Charophyta) and Ulva (Chlorophyta) and a putative XTH ancestral enzyme in Chara was identified. No XET activity was identified in the Rhodophyta or Phaeophyta.
XET activity was shown to be present in all major groups of green plants. These data suggest that an XET-related growth mechanism originated before the evolutionary divergence of the Chlorobionta and open new insights in the evolution of the mechanisms of primary cell wall expansion.
在被子植物中，木葡聚糖内转糖基酶（XET）/水解酶（XTH）参与生长和发育过程中细胞壁的重组。本研究检测了最早分化的现存植物，即苔藓植物和藻类直至褐藻门中寡聚木葡聚糖转糖基化活性的位置以及XTH表达序列标签（EST）的存在情况。这些结果提供了关于苔藓植物和藻类中XET生长机制存在的信息，并有助于总体上理解细胞壁伸长的进化。
将不同植物谱系的代表压在XET试纸上并进行检测。XET或与XET相关的活性通过荧光信号的掺入来可视化。在小立碗藓基因组数据库中筛选XTH的存在情况。此外，利用3' RACE技术搜索轮藻门中可能的XTH EST的存在情况。
在苔藓植物的三个主要类群中，在与生长区域相对应的部位发现了XET活性。在小立碗藓基因组中鉴定出两个推定的编码XTH的cDNA序列，它们包含对XET活性至关重要的所有结构域。此外，在轮藻（轮藻门）和石莼（绿藻门）的生长部位发现了XET活性，并在轮藻中鉴定出一种推定的XTH祖先酶。在红藻门或褐藻门中未鉴定出XET活性。
结果表明XET活性存在于所有主要的绿色植物类群中。这些数据表明，与XET相关的生长机制起源于绿藻纲进化分歧之前，为初级细胞壁扩展机制的进化提供了新的见解。
