Isolation and Characterization of ARRO-1 Genes from Apple Rootstocks in Response to Auxin Treatment

Abstract

To understand the role of the ARRO-1 gene in adventitious root formation, the coding sequences of ARRO-1 genes were isolated from apple rootstocks Chistock #1 and M9, and found to be 924 bp in size. Subcellular localization revealed that the ARRO-1 protein was localized to the plasma membrane. Real-time PCR analysis indicated that ARRO-1 was upregulated significantly by the auxins indole-3-butyric acid (IBA) and napthaleneacetic acid (NAA) compared to the auxin indole-3-acetic acid (IAA) and the hormone-free control. The transcript level of ARRO-1 reached its peak 24 h or 48 h after the onset of auxin treatment, and was maintained at a high level from 24–120 h, mostly coinciding with the induction phase of adventitious root formation. In general, there was greater upregulation of ARRO-1 in Chistock #1 than that in M9. In a rooting experiment with stem discs, no adventitious roots formed in the IAA or control treatments. Rooting frequencies in IBA and NAA treatments were significantly higher than in the fail-to-root treatments. Under IAA treatment, upregulation of ARRO-1 was higher than in the control but failed to induce any adventitious root formation, suggesting that involvement of ARRO-1 in adventitious rooting might be related more directly to auxin homeostasis rather than being rooting specific.