The Arabidopsis thaliana Double-Stranded RNA Binding Proteins DRB1 and DRB2 Are Required for miR160-Mediated Responses to Exogenous Auxin

DOUBLE-STRANDED RNA BINDING (DRB) proteins DRB1, DRB2, and DRB4 are essential for microRNA (miRNA) production in <i>Arabidopsis thaliana</i> (<i>Arabidopsis</i>) with miR160, and its target genes, <i>AUXIN RESPONSE FACTOR10</i> (<i>ARF10</i>), <i>ARF16</i>, and <i>ARF17</i>, forming an auxin responsive miRNA expression module crucial for root development. <b>Methods</b>: Wild-type <i>Arabidopsis</i> plants (Columbia-0 (Col-0)) and the <i>drb1</i>, <i>drb2</i>, and <i>drb12</i> mutants were treated with the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D), and the miR160-mediated response of these four <i>Arabidopsis</i> lines was phenotypically and molecularly characterized. <b>Results</b>: In 2,4-D-treated Col-0, <i>drb1</i> and <i>drb2</i> plants, altered miR160 abundance and <i>ARF10</i>, <i>ARF16</i>, and <i>ARF17</i> gene expression were associated with altered root system development. However, miR160-directed molecular responses to treatment with 2,4-D was largely defective in the <i>drb12</i> double mutant. In addition, via profiling of molecular components of the miR160 expression module in the roots of the <i>drb4</i>, <i>drb14</i>, and <i>drb24</i> mutants, we uncovered a previously unknown role for DRB4 in regulating miR160 production. <b>Conclusions</b>: The miR160 expression module forms a central component of the molecular and phenotypic response of <i>Arabidopsis</i> plants to exogenous auxin treatment. Furthermore, DRB1, DRB2, and DRB4 are all required in <i>Arabidopsis</i> roots to control miR160 production, and subsequently, to appropriately regulate <i>ARF10</i>, <i>ARF16</i>, and <i>ARF17</i> target gene expression.