Identification of Nitrogen Starvation-Responsive MicroRNAs in <em>Arabidopsis thaliana</em>

<div><p>microRNAs (miRNAs) are a class of negative regulators that take part in many processes such as growth and development, stress responses, and metabolism in plants. Recently, miRNAs were shown to function in plant nutrient metabolism. Moreover, several miRNAs were identified in the response to nitrogen (N) deficiency. To investigate the functions of other miRNAs in N deficiency, deep sequencing technology was used to detect the expression of small RNAs under N-sufficient and -deficient conditions. The results showed that members from the same miRNA families displayed differential expression in response to N deficiency. Upon N starvation, the expression of miR169, miR171, miR395, miR397, miR398, miR399, miR408, miR827, and miR857 was repressed, whereas those of miR160, miR780, miR826, miR842, and miR846 were induced. miR826, a newly identified N-starvation-induced miRNA, was found to target the <em>AOP2</em> gene. Among these N-starvation-responsive miRNAs, several were involved in cross-talk among responses to different nutrient (N, P, S, Cu) deficiencies. miR160, miR167, and miR171 could be responsible for the development of <em>Arabidopsis</em> root systems under N-starvation conditions. In addition, twenty novel miRNAs were identified and nine of them were significantly responsive to N-starvation. This study represents comprehensive expression profiling of N-starvation-responsive miRNAs and advances our understanding of the regulation of N homeostasis mediated by miRNAs.</p> </div

N-starvation-responsive miRNAs and their targets.

<p>Boldface letters indicate the previously validated targets. “*”indicates that no target was predicted. “+” and “−” indicate that up-regulation and down-regulation by N-starvation.</p

miR160, miR167, and miR171 are involved in development of root system under N starvation coditions.

<p>(A) More lateral roots in 35S::miR160a plants than WT (wild-type) plants. (B) Expression of miR160, miR167, miR171, and their targets under N starvation conditions. Gene expression values shown are relative to the expression in plants grown under normal MS medium, for which the value is set to 1. Error bars indicate ± SE obtained from three biological repeats. Values marked by an asterisk are significantly different from the corresponding control value with Student's <i>t</i>-test (<i>p</i><0.01; <i>n</i> = 3). (C) A putative work model for miRNA-mediated root growth under N starvation conditions.</p

Differentially expressed miRNAs in response to N deficiency.

<p>The significantly differentially expressed miRNAs with greater than 3-fold relative change were shown.</p

Axial 4,4′,6,6′-Tetrakis-trifluoromethyl-biphenyl-2,2′-diamine (TF-BIPHAM): Resolution and Applications in Asymmetric Hydrogenation

The racemic TF-BIPHAM was resolved for the first time, and the effectiveness of the resolved diamine was demonstrated by highly enantioselective hydrogenation of α-aryl enamides and α-dehydroamino acid esters using readily accessible bis(aminophosphine) ligands

miR826 is a N-starvation-induced miRNA.

<p>(A)Comparative analysis of miR826 precursor and its target <i>AOP2</i> sequences. The sequence in pink indicates mature miR826 sequence. (B) The position of miR826, <i>AOP1</i>, <i>AOP2</i>, and <i>AOP3</i> genes in chromosome. (C) The cleavage sites of <i>AOP2</i> transcripts. (D) Expression of miR826 and <i>AOP2</i> in response to N starvation. Gene expression values shown are relative to the expression in plants grown under normal MS medium, for which the value is set to 1. Error bars indicate ± SE obtained from three biological repeats. Values marked by an asterisk are significantly different from the corresponding control value with Student's <i>t</i>-test (<i>p</i><0.01; <i>n</i> = 3).</p

Differential expression of different miR169 species.

<p>(A) Four different mature miR169 species. (B) Expression of different miR169 members in response to different nutrient deficiencies. Gene expression values shown are relative to the expression in plants grown under normal MS medium, for which the value is set to 1. Error bars indicate ± SE obtained from three biological repeats. Values marked by an asterisk are significantly different from the corresponding control value with Student's <i>t</i>-test (<i>p</i><0.01; <i>n</i> = 3).</p

Identified targets of novel miRNAs from <i>Arabidopsis</i> degradome data.

<p>Vertical arrows indicate the target cleavage positions. The number indicates the number of corresponding cleavage products.</p

Novel miRNAs identified from deep sequencing data.

<p>Boldface letters indicate that the predicted target cleavages were identified from <i>Arabidopsis</i> degradome data.</p><p>“-” Indicates that no target was predicted. The miRNAs with a relative change ratio greater than 2 were underlined.</p

Axial 4,4′,6,6′-Tetrakis-trifluoromethyl-biphenyl-2,2′-diamine (TF-BIPHAM): Resolution and Applications in Asymmetric Hydrogenation

The racemic TF-BIPHAM was resolved for the first time, and the effectiveness of the resolved diamine was demonstrated by highly enantioselective hydrogenation of α-aryl enamides and α-dehydroamino acid esters using readily accessible bis(aminophosphine) ligands