Genome-Wide Identification, Characterization, and Expression Analysis of Calmodulin-Like Proteins (CMLs) in Apple

Calcium (Ca2+), a crucial second messenger in plants, is involved in diverse signaling pathways including biotic and abiotic stress responses. However, the functions of most calcium sensors including calcium-dependent protein kinases (CDPKs), calmodulins (CaMs), calmodulin-like proteins (CMLs), and calcineurin B-like proteins (CBLs) remain limited in plants, particularly in woody plants. Currently, a total of 83 CMLs and seven CaMs were discovered in the apple genome in this study. Functional domain analysis showed that these CMLs and CaMs contain a highly conserved EF-hand motif. qRT-PCR assays indicated that these CMLs were expressed ubiquitously in apple, including in the roots, stems, leaves, flowers, and fruits, and also possessed spatial specificity. Finally, most of these CMLs were induced by hormonal and abiotic stress, suggesting their potential roles in the regulation of growth, development, and the stress response in apple. In summary, our findings provide potential evidence that apple CMLs may be involved in abiotic stress and the regulation of plant growth and development.