Genome-wide identification of citrus CAMTA genes and their expression analysis under stress and hormone treatments

In plants, CAMTA (Calmodulin-binding transcription activator) proteins have been widely analysed, due to their vital roles in developmental regulation, environmental stress response, and hormone crosstalk. However, in citrus, this gene family, to date, has not been systematically characterised. In this study, 9 CitCAMTA genes have been identified from the citrus (Citrus sinensis and Citrus clementina) genomes. Their phylogenetic relationship, protein domain, exon-intron structure, and so forth were investigated in detail, revealing the divergence in their functions. Tissue-specific expression analysis showed that these CitCAMTA genes - with the exception of CitCAMTA4 - could be expressed in at least 1 tissue, indicating their roles in the development of root, stem, leaf, cotyledon, seed, and fruit peel. Under stress and hormone treatments, the expression patterns of each CitCAMTA remarkably varied, which showed a promising for improving citrus adaptation to stresses. Unexpectedly, the expression level of CitCAMTA4 was undetectable under all treatments. Taken together, our work lays a foundation for further analysis on citrus CAMTA genes, and provides a basic understanding of their roles in stress responses.