Kawashima Cintia Goulart, Yoshimoto Naoko, Maruyama-Nakashita Akiko, Tsuchiya Yumiko N, Saito Kazuki, Takahashi Hideki, Dalmay Tamas
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
Plant J. 2009 Jan;57(2):313-21. doi: 10.1111/j.1365-313X.2008.03690.x. Epub 2008 Oct 14.
Plants play an important role in the global sulphur cycle because they assimilate sulphur from the environment and build it into methionine and cysteine. Several genes of the sulphur assimilation pathway are regulated by microRNA-395 (miR395) that is itself induced by a low-sulphur (-S) environment. Here, we show that the six Arabidopsis miR395 loci are induced differently. We find that MIR395 loci are expressed in the vascular system of roots and leaves and root tips. Induction of miR395 by a -S environment in both roots and leaves suggests that translocation of miR395 from leaves to roots through the phloem is not necessary for plants growing on -S soil/medium. We also demonstrate that induction of miR395 is controlled by SLIM1, a key transcription factor in the sulphur assimilation pathway. Unexpectedly, the mRNA level of a miR395 target gene, SULTR2;1, strongly increases during miR395 induction in roots. We show that the spatial expression pattern of MIR395 transcripts in the vascular system does not appear to overlap with the expression pattern previously reported for SULTR2;1 mRNA. These results illustrate that negative temporal correlation between the expression level of a miRNA and its target gene in a complex tissue cannot be a requirement for target gene validation.
植物在全球硫循环中发挥着重要作用，因为它们从环境中吸收硫并将其合成蛋氨酸和半胱氨酸。硫同化途径的几个基因受微小RNA - 395（miR395）调控，而miR395本身由低硫（-S）环境诱导产生。在此，我们表明拟南芥的六个miR395基因座的诱导方式不同。我们发现MIR395基因座在根、叶的维管系统以及根尖中表达。根和叶中的-S环境均能诱导miR395，这表明对于在-S土壤/培养基上生长的植物而言，miR395通过韧皮部从叶向根的转运并非必需。我们还证明miR395的诱导受硫同化途径中的关键转录因子SLIM1控制。出乎意料的是，在根中miR395诱导过程中，其靶基因SULTR2;1的mRNA水平大幅增加。我们表明，维管系统中MIR395转录本的空间表达模式似乎与先前报道的SULTR2;1 mRNA的表达模式不重叠。这些结果表明，在复杂组织中，miRNA与其靶基因表达水平之间的负时相关系并非靶基因验证的必要条件。
