Buckhout Thomas J, Yang Thomas J W, Schmidt Wolfgang
Institute of Plant and Microbial Biology, Academia Sinica, 115 Taipei, Taiwan.
BMC Genomics. 2009 Apr 6;10:147. doi: 10.1186/1471-2164-10-147.
Iron (Fe) is an essential nutrient in plants and animals, and Fe deficiency results in decreased vitality and performance. Due to limited bio-availability of Fe, plants have evolved sophisticated adaptive alterations in development, biochemistry and metabolism that are mainly regulated at the transcriptional level. We have investigated the early transcriptional response to Fe deficiency in roots of the model plant Arabidopsis, using a hydroponic system that permitted removal of Fe from the nutrient solution within seconds and transferring large numbers of plants with little or no mechanical damage to the root systems. We feel that this experimental approach offers significant advantages over previous and recent DNA microarray investigations of the Fe-deficiency response by increasing the resolution of the temporal response and by decreasing non-Fe deficiency-induced transcriptional changes, which are common in microarray analyses.
The expression of sixty genes were changed after 6 h of Fe deficiency and 65% of these were found to overlap with a group of seventy-nine genes that were altered after 24 h. A disproportionally high number of transcripts encoding ion transport proteins were found, which function to increase the Fe concentration and decrease the zinc (Zn) concentration in the cytosol. Analysis of global changes in gene expression revealed that changes in Fe availability were associated with the differential expression of genes that encode transporters with presumed function in uptake and distribution of transition metals other than Fe. It appeared that under conditions of Fe deficiency, the capacity for Zn uptake increased, most probably the result of low specificity of the Fe transporter IRT1 that was induced upon Fe deficiency. The transcriptional regulation of several Zn transports under Fe deficiency led presumably to the homeostatic regulation of the cytosolic concentration of Zn and of other transition metal ions such as Mn to avoid toxicity.
The genomic information obtained from this study gives insights into the rapid transcriptional responses to Fe shortage in plants, and is important for understanding how changes in nutrient availability are translated into responses that help to avoid imbalances in ion distribution. We further identified rapidly induced or repressed genes with potential roles in perception and signaling during Fe deficiency which may aid in the elucidation of these processes.
铁（Fe）是动植物必需的营养元素，缺铁会导致活力和性能下降。由于铁的生物有效性有限，植物在发育、生物化学和代谢方面进化出了复杂的适应性变化，这些变化主要在转录水平上受到调控。我们使用水培系统研究了模式植物拟南芥根系对缺铁的早期转录反应，该系统能够在数秒内从营养液中去除铁，并将大量根系几乎没有或没有机械损伤的植物转移过来。我们认为，这种实验方法比以前和最近通过DNA微阵列研究缺铁反应具有显著优势，它提高了时间反应的分辨率，并减少了非缺铁诱导的转录变化，而这种变化在微阵列分析中很常见。
缺铁6小时后，60个基因的表达发生了变化，其中65%与24小时后改变的79个基因重叠。发现编码离子转运蛋白的转录本数量异常高，这些蛋白的功能是增加细胞质中铁的浓度并降低锌（Zn）的浓度。对基因表达的全局变化分析表明，铁有效性的变化与编码转运蛋白的基因的差异表达有关，这些转运蛋白在除铁之外的过渡金属的吸收和分布中可能具有假定的功能。似乎在缺铁条件下，锌的吸收能力增加，这很可能是缺铁诱导的铁转运蛋白IRT1特异性较低的结果。缺铁条件下几种锌转运的转录调控可能导致细胞质中锌和其他过渡金属离子（如锰）浓度的稳态调节，以避免毒性。
本研究获得的基因组信息有助于深入了解植物对铁短缺的快速转录反应，对于理解营养有效性的变化如何转化为有助于避免离子分布失衡的反应非常重要。我们进一步鉴定了在缺铁期间在感知和信号传导中具有潜在作用的快速诱导或抑制的基因，这可能有助于阐明这些过程。
