Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Ann Bot. 2010 Jun;105(7):1109-17. doi: 10.1093/aob/mcq002. Epub 2010 Mar 2.
Under conditions of low iron availability, rice plants induce genes involved in iron uptake and utilization. The iron deficiency-responsive cis-acting element binding factors 1 and 2 (IDEF1 and IDEF2) regulate transcriptional response to iron deficiency in rice roots. Clarification of the functions of IDEF1 and IDEF2 could uncover the gene regulation mechanism.
Spatial patterns of IDEF1 and IDEF2 expression were analysed by histochemical staining of IDEF1 and IDEF2 promoter-GUS transgenic rice lines. Expression patterns of the target genes of IDEF1 and IDEF2 were analysed using transformants with induced or repressed expression of IDEF1 or IDEF2 grown in iron-rich or in iron-deficient solutions for 1 d.
IDEF1 and IDEF2 were highly expressed in the basal parts of the lateral roots and vascular bundles. IDEF1 and IDEF2 expression was dominant in leaf mesophyll and vascular cells, respectively. These expression patterns were similar under both iron-deficient and iron-sufficient conditions. IDEF1 was strongly expressed in pollen, ovaries, the aleurone layer and embryo. IDEF2 was expressed in pollen, ovaries and the dorsal vascular region of the endosperm. During seed germination, IDEF1 and IDEF2 were expressed in the endosperm and embryo. Expression of IDEF1 target genes was regulated in iron-rich roots similar to early iron-deficiency stages. In addition, the expression patterns of IDEF2 target genes were similar between iron-rich conditions and early or subsequent iron deficiency.
IDEF1 and IDEF2 are constitutively expressed during both vegetative and reproductive stages. The spatial expression patterns of IDEF1 and IDEF2 overlap with their target genes in restricted cell types, but not in all cells. The spatial expression patterns and gene regulation of IDEF1 and IDEF2 in roots are generally conserved under conditions of iron sufficiency and deficiency, suggesting complicated interactions with unknown factors for sensing and transmitting iron-deficiency signals.
在铁供应不足的情况下，水稻植株会诱导参与铁吸收和利用的基因。铁缺乏响应顺式作用元件结合因子 1 和 2（IDEF1 和 IDEF2）调节水稻根系对铁缺乏的转录响应。阐明 IDEF1 和 IDEF2 的功能可以揭示基因调控机制。
通过 IDEFl 和 IDEF2 启动子-GUS 转基因水稻株系的组织化学染色分析 IDEFl 和 IDEF2 的表达的空间模式。使用在富含铁或缺铁溶液中生长 1 天的诱导或抑制表达 IDEF1 或 IDEF2 的转化体分析 IDEF1 和 IDEF2 的靶基因的表达模式。
IDEFl 和 IDEF2 在侧根和维管束的基部高度表达。IDEF1 和 IDEF2 的表达分别在叶片叶肉和维管束细胞中占优势。在缺铁和铁充足条件下，这些表达模式相似。IDEF1 在花粉、子房、糊粉层和胚中强烈表达。IDEF2 在花粉、子房和胚乳的背侧血管区表达。在种子萌发过程中，IDEF1 和 IDEF2 在胚乳和胚中表达。IDEF1 靶基因的表达在富含铁的根中受到调节，类似于早期缺铁阶段。此外，IDEF2 靶基因的表达模式在富含铁的条件下与早期或随后的缺铁相似。
IDEF1 和 IDEF2 在营养和生殖阶段都持续表达。IDEF1 和 IDEF2 的空间表达模式与受其调控的基因在特定细胞类型中重叠，但并非在所有细胞中都重叠。在铁充足和缺乏条件下，IDEF1 和 IDEF2 在根部的空间表达模式和基因调控通常是保守的，这表明对于铁缺乏信号的感应和传递存在复杂的相互作用与未知因素。
