SQUAMOSA promoter binding protein‐like7 regulated microRNA408 is required for vegetative development in Arabidopsis

Abstract

SUMMARYMicroRNAs (miRNAs) are endogenous small RNAs repressing target gene expression post-transcriptionally and are critically involved in various development processes and responses to environmental stresses. MiR408 is highly conserved in land plants and targets several transcripts encoding copper proteins. Although it has been well documented that expression level of miR408 is strongly influenced by a variety of environmental conditions including copper availability, the biological function of this miRNA is still unknown. Here we show that constitutive expression of miR408 results in enhanced growth of seedling and adult plant while knocking down miR408 level by T-DNA insertions or the artificial miRNA technique causes impaired growth. Further, we found that constitutively activated miR408 is able to complement the growth defects of the T-DNA lines. Regarding the molecular mechanism governing miR408 expression, we found that the transcription factors SQUAMOSA PROMOTER BINDING PROTEIN-LIKE7 (SPL7) binds to the GTAC motifs in the MIR408 promoter in response to copper deficiency. Interestingly, constitutive activation of miR408 in the spl7 background could partially rescue the severe growth defects of the mutant. Together these results demonstrate that miR408 is a powerful modulator of vegetative growth. Our finding thus reveals a novel control mechanism for vegetative development based on calculated miR408 expression in response to environmental cues.

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“…Accordingly, Northern blotting, quantitative real-time PCR (qRT-PCR), microarrays, and deep sequencing have been extensively used to quantify endogenous miRNAs and, thereby, infer changes in their activity (Navarro et al, 2006;Liu et al, 2008;Moxon et al, 2008a;Hsieh et al, 2009;Lv et al, 2010). miRNA levels may be regulated at multiple steps during their biogenesis, such as MIR gene expression (Liu et al, 2008;Jeong et al, 2011;Cho et al, 2012;Hajdarpasic and Ruggenthaler, 2012;Liang et al, 2012;Zhang and Li, 2013), processing of miRNA precursors Yan et al, 2012) or miRNA stability (Ramachandran and Chen, 2008). However, studies in animals indicate that the miRNA pathway is extensively regulated also downstream of miRNA biogenesis (Leung and Sharp, 2007), and that the extent of target repression cannot be entirely predicted from the abundance of its regulatory miRNA (Brown et al, 2007).…”