Cloning and functional analysis of MdCRCT1 in the regulation of drought tolerance in apple

Abiotic stresses, particularly drought stress, impose a profound adverse effect on plant proliferation and development. Multiple categories of transcription factors have been associated with the modulation of stress responses in plants. CONSTANS, CONSTANS-like and TOC1 (CCT) proteins are transcription factors that contribute significantly to plant resilience under environmental stress, yet little is known about their role in apple and other woody plants. In this study, 28 members of the apple CCT Motif Family (CMF) subfamily, which all contain conserved CCT domains, were identified in the apple genome. qRT-PCR investigation demonstrated that the MdCMF genes were extensively distributed in diverse tissues and organs. Among them, the CO₂-responsive CCT protein MdCRCT1 was significantly induced by drought stress, with its transcript level increasing approximately 4-fold at 1 h. Overexpression of MdCRCT1 enhanced drought tolerance in both apple calli and Arabidopsis, as evidenced by improved growth and reduced reactive oxygen species (ROS) accumulation under drought stress. This enhanced tolerance was mechanistically linked to the transcriptional upregulation of drought-responsive genes by MdCRCT1 in Arabidopsis, revealing a novel role for this regulator in drought stress adaptation. This study presents the first functional characterization of a CMF gene, MdCRCT1, in woody plants, thereby establishing a foundation for investigating the role of CMF genes in apple under environmental stress.