Fujii Hiroaki, Chiou Tzyy-Jen, Lin Shu-I, Aung Kyaw, Zhu Jian-Kang
Institute for Integrative Genome Biology and Department of Botany and Plant Sciences, University of California, Riverside, Riverside, California 92521, USA.
Curr Biol. 2005 Nov 22;15(22):2038-43. doi: 10.1016/j.cub.2005.10.016.
Although microRNAs (miRNAs) have been documented to regulate development in plants and animals , the function of miRNAs in physiology is unclear. miR399 has multiple target sites in the 5' untranslated region (UTR) of a gene encoding a putative ubiquitin-conjugating enzyme (UBC) in Arabidopsis thaliana. We report here that miR399 was highly induced, whereas the target UBC mRNA was reduced by low-phosphate (Pi) stress. In transgenic plants with constitutive expression of miR399, UBC mRNA accumulation was suppressed even under high Pi. The expression of transgene UBC mRNA with 5' UTR miR399 target sites, but not the one without 5' UTR, was reduced under low-Pi condition. Furthermore, transgenic Arabidopsis plants with constitutive expression of miR399 accumulated more Pi than the wild-type, and transgenic plants expressing the UBC mRNA without 5' UTR (miRNA-deregulated) showed less inhibition of primary root growth and less induction of a Pi transporter gene by low-Pi stress than those of wild-type plants. We conclude that miR399 downregulates UBC mRNA accumulation by targeting the 5' UTR, and this regulation is important for plant responses to Pi starvation. The results suggest that miRNAs have functional roles for plants to cope with fluctuations in mineral-nutrient availability in the soil.
尽管微小RNA（miRNA）已被证明可调控动植物的发育，但其在生理学中的功能尚不清楚。miR399在拟南芥中一个编码假定泛素结合酶（UBC）的基因的5'非翻译区（UTR）有多个靶位点。我们在此报告，低磷（Pi）胁迫可高度诱导miR399，而其靶标UBC mRNA会减少。在组成型表达miR399的转基因植物中，即使在高磷条件下，UBC mRNA的积累也受到抑制。在低磷条件下，带有5'UTR miR399靶位点的转基因UBC mRNA的表达降低，而没有5'UTR的则不然。此外，组成型表达miR399的转基因拟南芥植物比野生型积累更多的磷，并且表达没有5'UTR的UBC mRNA（miRNA失调）的转基因植物在低磷胁迫下主根生长的抑制作用较小，对Pi转运蛋白基因的诱导作用也小于野生型植物。我们得出结论，miR399通过靶向5'UTR下调UBC mRNA的积累，并且这种调控对植物对磷饥饿的反应很重要。结果表明，miRNA在植物应对土壤中矿质营养有效性波动方面具有功能性作用。
