Institute for Plant Molecular and Developmental Biology, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße, Düsseldorf, Germany.
Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, UK.
J Exp Bot. 2018 Sep 14;69(20):4897-4906. doi: 10.1093/jxb/ery263.
The bundle sheath provides a conduit linking veins and mesophyll cells. In the C3 plant Arabidopsis thaliana, it also plays important roles in oxidative stress and sulphur metabolism. However, the mechanisms responsible for the patterns of gene expression that underpin these metabolic specializations are poorly understood. Here, we used the Arabidopsis SULTR2;2 gene as a model to better understand mechanisms that restrict expression to the bundle sheath. Deletion analysis indicated that the SULTR2;2 promoter contains a short region necessary for expression in the bundle sheath and veins. This sequence acts as a positive regulator and is tolerant to multiple consecutive deletions indicating considerable redundancy in the cis-elements involved. It is highly conserved in SULTR2;2 genes of the Brassicaceae and is functional in the distantly related C4 species Flaveria bidentis that belongs to the Asteraceae. We conclude that expression of SULTR2;2 in the bundle sheath and veins is underpinned by a highly redundant sequence that likely represents an ancient and conserved mechanism found in families as diverse as the Asteraceae and Brassicaceae.
束鞘提供了一个连接叶脉和叶肉细胞的通道。在 C3 植物拟南芥中，它在氧化应激和硫代谢中也起着重要作用。然而，负责这些代谢特化的基因表达模式的机制还知之甚少。在这里，我们使用拟南芥 SULTR2;2 基因作为模型，以更好地理解限制其在束鞘和叶脉中表达的机制。缺失分析表明，SULTR2;2 启动子包含一个短序列，对于在束鞘和叶脉中的表达是必需的。该序列作为一个正调控因子，并且能够耐受多个连续缺失，表明所涉及的顺式元件具有相当大的冗余性。它在拟南芥科的 SULTR2;2 基因中高度保守，并且在远缘的菊科植物 Flaveria bidentis 中具有功能，后者属于菊科。我们得出结论，SULTR2;2 在束鞘和叶脉中的表达是由一个高度冗余的序列支撑的，该序列可能代表了在菊科和十字花科等不同家族中发现的古老而保守的机制。
