Genome-wide identification of AUX/IAA in radish and functional characterization of RsIAA33 gene during taproot thickening.

Auxin/indole-3-acetic acid (Aux/IAA) genes encode short lived nuclear proteins that cooperated with auxin or auxin response factor (ARF), which are involved in plant growth and developmental processes. However, it's still ambiguous how the Aux/IAA genes regulate the process governing taproot thickening in radish. Herein, 65 Aux/IAA genes were identified from the radish genome. Gene duplication analysis showed that two pairs of tandem duplication and 17 (27%) segmental duplication events were identified among Aux/IAA family genes in radish. Transcriptomic analysis revealed that most of Aux/IAA genes (52/65) exhibited differential expression pattern in different root tissues, and six root-specific genes were highly expressed in root cortex, cambium, xylem, and root tip in radish. RT-qPCR analysis showed that the expression level of RsIAA33 was the highest at cortex splitting stage (CSS), and early expanding stage (ES). Furthermore, amiRNA-mediated gene silencing of RsIAA33 indicated that it could inhibit the reproductive growth, thus promoting taproot thickening and development. These results would provide valuable information for elucidating the molecular function of Aux/IAA genes involved in taproot thickening in radish.