R2R3-MYB Transcription Factor MdMYB73 Confers Increased Resistance to the Fungal Pathogen <i>Botryosphaeria dothidea</i> in Apples <i>via</i> the Salicylic Acid Pathway

Abstract

MYB transcription factors (TFs) participate in many biological processes. However, the molecular mechanisms by which MYB TFs affect plant resistance to apple ring rot remain poorly understood. Here, the R2R3-MYB gene <i>MdMYB73</i> was cloned from "<i>Royal Gala</i>" apples and functionally characterized as a positive regulator of the defense response to <i>Botryosphaeria dothidea</i>. qRT-PCR and GUS staining demonstrated that <i>MdMYB73</i> was strongly induced in apple fruits and transgenic calli after inoculation with <i>B. dothidea</i>. <i>MdMYB73</i> overexpression improved resistance to <i>B. dothidea</i> in apple calli and fruits, while <i>MdMYB73</i> suppression weakened. Increased resistance to <i>B. dothidea</i> was also observed in <i>MdMYB73</i>-expressing <i>Arabidopsis thaliana</i>. Interestingly, salicylic acid (SA) contents and the expression levels of genes related with SA synthesis and signaling were greater in <i>MdMYB73</i>-overexpressing plant materials compared to wild-type controls after inoculation, suggesting that MdMYB73 might enhance resistance to <i>B. dothidea</i> <i>via</i> the SA pathway. Finally, we discovered that MdMYB73 interacts with MdWRKY31, a positive regulator of <i>B. dothidea</i>. Together, MdWRKY31 and MdMYB73 enhanced <i>B. dothidea</i> resistance in apples. Our results clarify the mechanisms by which MdMYB73 improves resistance to <i>B. dothidea</i> and suggest that resistance may be affected by regulating the SA pathway.