A Novel Arabidopsis microRNA promotes IAA biosynthesis via the indole-3-acetaldoxime pathway by suppressing superroot1.

IAA is a plant hormone that plays important roles in regulating growth and responses to environmental changes. Indole-3-acetaldoxime (IAOx) has been proposed as an important intermediate in the biosynthesis of IAA and two other indole compounds, indole glucosinolates and camalexin. Although the IAOx-dependent IAA biosynthesis pathway has been well studied, the mechanisms of its regulation remain elusive. Here, we report the identification of a novel microRNA, miR10515, which targets superroot1 (SUR1), the gene encoding an indole glucosinolate biosynthetic enzyme. miR10515 was induced by high temperature. Overexpression of MIR10515 resulted in a high-IAA phenotype, while the loss of function of miR10515 resulted in a low-IAA phenotype; these phenotypes were more severe at high temperature. Our results further demonstrated that miR10515 promoted IAA biosynthesis via the IAOx pathway by blocking the indole glucosinolate and camalexin biosynthetic pathways. Phytochrome interacting factor4 (PIF4), a dominant regulator of plant development in response to high temperature, was not required for miR10515 expression. These results provide information on the IAOx metabolic branching point and its biological importance.