1. ¹National Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Shanghai Institute for Biological Sciences, 300 Fenglin Road, Shanghai 200032, China
2. ²SIBS-SJTU-PSU Joint Center for Life Sciences, Shanghai Institute of Plant Physiology and Ecology, Shanghai Institute for Biological Sciences, 300 Fenglin Road, Shanghai 200032, China
3. ³Department of Biology and the Huck Institute for the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA

Correspondence: Hai Huang, Tel: 21-64042090; Fax: 21-64042385; E-mail: hhuang@iris.sipp.ac.cn

Received 18 January 2006; Revised 8 February 2006; Accepted 26 February 2006.

Abstract

The plant hormone auxin plays a critical role in regulating plant growth and development. Recent advances have been made in the understanding of auxin response pathways, primarily by the characterization of auxin response mutants in Arabidopsis. In addition, microRNAs (miRNAs) have been shown to be critical regulators of genes important for normal plant development and physiology. However, little is known about possible interactions between miRNAs and hormonal signaling during normal development. Here we show that an Arabidopsis microRNA, miR167, which has a complementary sequence to a portion of the AUXIN RESPONSE FACTOR6 (ARF6) and ARF8 mRNAs, can cause transcript degradation for ARF8, but not for ARF6. We report phenotypic characterizations of 35S::MIR167b transgenic lines, and show that severe 35S::MIR167b transgenic lines had phenotypes similar to those of an arf6 arf8 double mutant. The transgenic phenotypes suggest that miR167 may repress ARF6 at the level of translation. We demonstrate that the transgenic plants are defective in all four whorls of floral organs. In the transgenic flowers, filaments were abnormally short, anthers could not properly release pollen, and pollen grains did not germinate. Our results provide an important link between the miRNA-mediated regulatory pathway of gene expression and the auxin signaling network promoting plant reproductive development.