Genome-wide identification and expression profiling of the calmodulin-binding transcription activator gene family in apple (Malus × domestica) under biotic and abiotic stress conditions

Calmodulin-binding transcription activators (CAMTAs) are pivotal regulators that integrate calcium signaling with plant developmental and stress-response programs. This study identified eight MdCAMTA genes in the apple ( Malus domestica ) genome, which encode 13 isoforms through alternative splicing. Phylogenetic analysis indicated that MdCAMTA proteins cluster into two ancient clades, with a divergence predating the speciation of dicots. Promoter analysis identified a complex cis-regulatory landscape dominated by light-responsive elements, binding sites for MYB, MYC, and WRKY factors, and various phytohormone-responsive motifs. Transcriptomic profiling revealed pronounced tissue specificity, particularly in pollen, where a unique reciprocal expression pattern suggests stringent spatial control of CAMTA signaling. Furthermore, MdCAMTA genes exhibited highly specific responses to environmental challenges: MdCAMTA1.2 emerged as a potential marker for hypoxic adaptation and viral response, while MdCAMTA5.2 is a candidate regulator for nutrient homeostasis and fungal defense. These findings establish a foundational genomic framework for understanding how MdCAMTA genes coordinate apple resilience through multifaceted hormonal and environmental signaling.