Functional characterisation of <i>MdMYB44</i> as a negative regulator in the response to cold and salt stress in apple calli

<p>MYB (v-myb avian myeloblastosis viral oncogene homolog) transcription factors (TFs) participate in the abiotic stress response in several plant species. In this study, we cloned and characterised <i>MdMYB44</i> from apple (<i>Malus domestica</i>). Phylogenetic analysis showed that the MdMYB44 protein was highly homologous to <i>Arabidopsis thaliana</i> MYB44. In addition, MdMYB44 localised to the nuclei in transformed onion epidermal cells and showed transcriptional activation activity in a yeast one-hybrid assay. <i>MdMYB44</i> was expressed in the stem, leaves, roots, flowers, and fruits, with the highest transcript level being observed in the leaves. Quantitative PCR analysis demonstrated that <i>MdMYB44</i> expression was down-regulated by cold, osmotic, and salt stresses. Furthermore, stable overexpression of <i>MdMYB44</i> in transgenic apple calli remarkably alleviated their tolerance to high salinity and cold, and relative conductivity and malondialdehyde accumulation under salt and cold treatments were significantly higher than those in wild-type control calli. Therefore, our findings provide evidence that <i>MdMYB44</i> is involved in susceptibility to cold and salt stress in apple calli and indicate MdMYB44 to negatively regulate plant abiotic stress defence.</p>