Effects of hypergravity on expression of XTH genes in azuki bean epicotyls
Effects of hypergravity on expression of XTH genes in azuki bean epicotyls
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DOI：
10.1111/j.1399-3054.2007.00949.x
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发表时间：
2007-10-01
影响因子：
6.4
通讯作者：
Hoson, Takayuki
中科院分区：
文献类型：
--
作者：
Soga, Kouichi;Wakabayashi, Kazuyuki;Hoson, Takayuki
离心产生的超重力抑制了红豆上胚轴的伸长生长，降低了细胞壁的伸长性。此外，超重增加了木葡聚糖的分子质量，而降低了木葡聚糖在上胚轴上的降解活性。对3个木葡聚糖内转糖苷酶/水解酶（XTH）基因VaXTHS4、VaXTH1和VaXTH2在超重力条件下的表达谱进行分析发现，只显示水解酶活性的VaXTHS4的表达量与重力的对数成比例下调（R = -0.94）。而VaXTH1或VaXTH2的基因表达则不受重力条件的影响，仅表现出转糖苷酶活性。将在1 g条件下生长的幼苗转移到300 g的超重力条件下，在1 h内检测到VaXTHS4的表达下调。去除超重力刺激后，VaXTHS4的表达在1 h内增加。这些结果表明，在重力刺激下，红豆上胚轴仅及时调节VaXTHS4的表达水平。VaXTHS4表达的变化对木葡聚糖水解活性的调节可能与木葡聚糖分子量的重力调节有关，从而导致细胞壁力学性能和细胞伸长的改变。镧和钆是机械敏感钙离子可渗透通道（机械感受器）的潜在阻滞剂，可使VaXTHS4表达的抑制作用消失，提示机械感受器参与了超重力对VaXTHS4表达的抑制。
Hypergravity produced by centrifugation caused inhibition of elongation growth and a decrease in the cell wall extensibility in azuki bean epicotyls (Vigna angularis Ohwi et Ohashi). Also, hypergravity increased the molecular mass of xyloglucans, whereas it decreased xyloglucan-degrading activity in epicotyls. When the expression profiles of three xyloglucan endotransglucosylase/hydrolase (XTH) genes, VaXTHS4, VaXTH1 and VaXTH2, were analyzed under hypergravity conditions, the expression of VaXTHS4, which shows only hydrolase activity, was downregulated in proportion to the logarithm of the magnitude of gravity (R = -0.94). However, the gene expression of VaXTH1 or VaXTH2, which shows only transglucosylase activity, was not affected by gravitational conditions. When the seedlings that had been grown at 1 g were transferred to hypergravity conditions at 300 g, the downregulation of VaXTHS4 expression was detected within 1 h. By removal of hypergravity stimulus, VaXTHS4 expression was increased within 1 h. These results suggest that azuki bean epicotyls promptly regulate the expression level of only VaXTHS4 in response to gravity stimuli. The regulation of xyloglucan-hydrolyzing activity as a result of changes in VaXTHS4 expression may be involved in the regulation by gravity of molecular mass of xyloglucans, leading to modifications of cell wall mechanical properties and cell elongation. Lanthanum and gadolinium, potential blockers of mechanosensitive calcium ion permeable channels (mechanoreceptors), nullified the suppression of VaXTHS4 expression, suggesting that mechanoreceptors are responsible for inhibition by hypergravity of VaXTHS4 expression.