Two azuki bean XTH genes, VaXTH1 and VaXTH2, with similar tissue-specific expression profiles, are differently regulated by auxin
Two azuki bean XTH genes, VaXTH1 and VaXTH2, with similar tissue-specific expression profiles, are differently regulated by auxin
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DOI：
10.1093/pcp/pcg002
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发表时间：
2003-01-01
影响因子：
4.9
通讯作者：
Nishitani, K
中科院分区：
文献类型：
--
作者：
Nakamura, T;Yokoyama, R;Nishitani, K
为了深入了解XTH（木葡聚糖内切转葡糖基酶/水解酶）基因家族的功能多样性，我们分析了两个红豆基因VaXTH 1和VaXTH 2的表达谱，这两个基因在氨基酸序列上具有惊人的相似性。这两个XTH基因表现出基本相似的组织特异性表达谱，因为这两种mRNA主要存在于生长节间的韧皮纤维中。然而，它们的表达谱并不相同。VaXTH 1在节间基部的木质部细胞中表达，而VaXTH 2在木质部中很少或没有表达。此外，它们表现出空间上不同的RNA分布曲线沿着节间，VaXTH 1被表达更接近顶部的节间比VaXTH 2。这表明它们在韧皮纤维发育期间的表达谱在时间上不同。吲哚-3-乙酸（IAA）上调这两种mRNA水平。然而，IAA对VaXTH 1基因的这种作用在0.25 M甘露醇中无效，这阻止了细胞扩增而不影响生长素本身的作用。相反，IAA诱导的VaXTH 2基因的上调不受甘露醇的影响。此外，促进酸化和生长的fusicoccin上调VaXTH 1表达，但不上调VaXTH 2表达。因此，这两个XTH基因在韧皮纤维发育的不同阶段，在同一细胞类型中参与细胞壁动态的不同步骤，并以不同的方式受到IAA的调控。
To gain insight into the functional diversity of the XTH (xyloglucan endotransglucosylase/hydrolase) gene family, we analyzed the expression profiles of two azuki bean genes, VaXTH1 and VaXTH2, which share a striking resemblance in their amino acid sequences. The two XTH genes exhibit essentially similar tissue-specific expression profiles, in that both mRNAs are found predominantly in the phloem fibers of growing internodes. However, their expression profiles are not identical. Whereas VaXTH1 is expressed in xylem cells in the basal part of the internode, little or no expression of VaXTH2 is found in the xylem. Furthermore, they exhibit spatially divergent RNA distribution profiles along the internode, VaXTH1 being expressed nearer to the top of the internode than VaXTH2. This indicates their temporally divergent expression profiles during development of the phloem fiber. Indole-3-acetic acid (IAA) up-regulates both of the mRNA levels. However, this effect of IAA on the VaXTH1 gene is nullified in 0.25 M mannitol, which prevents cell expansion without affecting auxin action per se. In contrast, the IAA-induced up-regulation of the VaXTH2 gene is not affected by mannitol. Furthermore, fusicoccin, which promotes acidification and growth, up-regulates VaXTH1 expression, but not VaXTH2 expression. Thus, the two XTH genes are committed to different steps of the cell wall dynamics in the same cell type at different stages of phloem fiber development, and are regulated by IAA in different ways.