The Early Nodulin Gene Enod2: Symbiotic Control and Cytokinin Induction

根瘤素基因是豆科植物固氮根瘤形成过程中特异性诱导的植物基因。早期根瘤素（Enod）基因在接种后10天内表达，在根瘤菌侵染过程和根瘤发生中发挥作用。Enod基因不仅受共生诱导和发育控制，而且以组织特异性的方式表达。Enod2基因在根瘤薄壁细胞中被共生激活，并编码一种富含羟基脯氨酸的蛋白质，该蛋白质可能针对植物细胞壁，在那里它可能参与创建氧气扩散屏障。本研究的重点是阐明热带茎结豆科植物Sesbania rostrata （SrEnod2）中Enod2基因表达的信号转导途径。SrEnod2基因可以被生理上显著浓度的细胞分裂素快速特异性诱导。因此，该基因不仅是研究植物根瘤特异性基因表达的理想候选基因，而且是研究细胞分裂素诱导植物基因的独特模型。操纵细菌“诱导剂”的能力为研究植物细胞分裂和分化过程提供了强有力的实验方法。

Nodulin genes are plant genes which are specifically induced during the formation of nitrogen-fixing root- stem nodules on leguminous plants. Early nodulin (Enod) genes are expressed within 10 days after inoculation and play a role in the rhizobial infection process and nodule ontogeny. Enod genes are not only symbiotically induced and developmentally controlled, but are also expressed in a tissue specific manner. The Enod2 gene is symbiotically activated in the nodule parenchyma cells and encodes a hydroxyproline rich protein, which probably is targeted to the plant cell wall, where it may be involved in creating an oxygen diffusion barrier. The focus of this proposal is to elucidate the signal transduction pathway involved in the expression of the Enod2 gene from the tropical stem-nodulated legume, Sesbania rostrata (SrEnod2). The SrEnod2 gene can be induced rapidly and specifically by physiologically significant concentrations of cytokinins. This gene is therefore not only an ideal candidate to study nodule-specific plant gene expression, but also serves as a unique model to study plant gene induction be cytokinin. The ability to manipulate the bacterial "inducer" offers a powerful experimental approach to study the process of plant cell division and differentiation.