Genome-Wide Characterization of IQD Family Proteins in Apple and Functional Analysis of the Microtubule-Regulating Abilities of MdIQD17 and MdIQD28 under Cold Stress

Microtubules undergo dynamic remodeling in response to diverse abiotic stress in plants. The plant-specific IQ67 DOMAIN (IQD) family proteins serve as microtubule-associated proteins, playing multifaceted roles in plant development and response to abiotic stress. However, the biological function of <i>IQD</i> genes in apple remains unclear. In this study, we conducted a comprehensive analysis of the <i>Malus domestica</i> genome, identifying 42 <i>IQD</i> genes distributed across 17 chromosomes and categorized them into four subgroups. Promoter analysis revealed the presence of stress-responsive elements. Subsequent expression analysis highlighted the significant upregulation of <i>MdIQD17</i> and <i>MdIQD28</i> in response to cold treatments, prompting their selection for further functional investigation. Subcellular localization studies confirmed the association of <i>MdIQD17</i> and <i>MdIQD28</i> with microtubules. Crucially, confocal microscopy and quantification revealed diminished microtubule depolymerization in cells transiently overexpressing <i>MdIQD17</i> and <i>MdIQD28</i> compared to wild-type cells during cold conditions. In conclusion, this study provides a comprehensive analysis of <i>IQD</i> genes in apple, elucidating their molecular mechanism in response to cold stress.