Screening of cDNA expression libraries derived from plants exposed to stress, with 35S-labeled recombinant calmodulin as a probe, revealed a new family of proteins containing a transcription activation domain and two types of DNA-binding domains designated the CG-1 domain (pfam03859) and the transcription factor immunoglobulin domain (pfam01833), ankyrin repeats (pfam1279), and a varying number of IQ calmodulin-binding motifs (pfam00612) (Finkler et al., 2007).

Based on domain organization and amino acid sequence comparisons, similar proteins, with the same domain organization, were identified in the genomes of other multicellular organisms including human, Drosophila, and Caenorhabditis, whereas none were found in the complete genomes of single cell eukaryotes and prokaryotes.

This family of proteins was designated calmodulin-binding transcription activators (CAMTAs). Arabidopsis thaliana contains six CAMTA genes (AtCAMTA1-AtCAMTA6). The transcription activation domain of AtCAMTA1 was mapped by testing a series of protein fusions with the DNA-binding domain of the bacterial LexA transcription factor and two reporter genes fused to LexA recognition sequences in yeast cells. Two human proteins designated HsCAMTA1 and HsCAMTA2 were also shown to activate transcription in yeast using the same reporter system. Subcellular fractionation of Arabidopsis tissues revealed the presence of CAMTAs predominantly in the nucleus. Calmodulin binding assays identified a region of 25 amino acids capable of binding calmodulin with high affinity (K(d) = 1.2 nm) in the presence of calcium. We suggest that CAMTAs comprise a conserved family of transcription factors in a wide range of multicellular eukaryotes, which possibly respond to calcium signaling by direct binding of calmodulin (Finkler et al., 2007).

In the rice (Oryza sativa), maize (Zea mays), and wheat (Triticum aestivum) genomes there are 7, 9, and 15  CAMTA genes respectively (Yue et al., 2015, Yang et al., 2020, Gain et al., 2022) . Phylogenetic trees classified these seven CAMTA genes into three clades indicating the evolutionary conservation in gene structure and their association with other plant species (Gain et al., 2022). An expression study in 12 representative plant species revealed significant species specificity, tissue specificity, and developmental stage specificity of CAMTAs. This study also indicated that the CAMTA genes might promote maturation and senescence. The expression levels and regulatory networks of CAMTAs revealed that CAMTAs could enhance cold tolerance of rice by regulating carbohydrate metabolism-related genes to accumulate carbohydrates or by modulating target genes together with other transcription factors (Xiao et al., 2021). In maize most CAMTA genes respond to both abiotic and biotic stress (Yue et al., 2015).

Last updated June 2023 by John Gray

References:

Finkler A, Ashery-Padan R, Fromm H. CAMTAs: calmodulin-binding transcription activators from plants to human. FEBS Lett. 2007 Aug 21;581(21):3893-8. doi: 10.1016/j.febslet.2007.07.051. Epub 2007 Aug 1. PMID: 17689537

Gain H, Nandi D, Kumari D, Das A, Dasgupta SB, Banerjee J. Genome‑wide identification of CAMTA gene family members in rice (Oryza sativa L.) and in silico study on their versatility in respect to gene expression and promoter structure. Funct Integr Genomics. 2022 Apr;22(2):193-214. doi: 10.1007/s10142-022-00828-w. Epub 2022 Feb 16. PMID: 35169940

Xiao P, Feng JW, Zhu XT, Gao J. Evolution Analyses of CAMTA Transcription Factor in Plants and Its Enhancing Effect on Cold-tolerance. Front Plant Sci. 2021 Nov 1;12:758187. doi: 10.3389/fpls.2021.758187. PMID: 34790215; PMCID: PMC8591267.

Yang F, Dong FS, Hu FH, Liu YW, Chai JF, Zhao H, Lv MY, Zhou S. Genome-wide identification and expression analysis of the calmodulin-binding transcription activator (CAMTA) gene family in wheat (Triticum aestivum L.). BMC Genet. 2020 Sep 14;21(1):105. doi: 10.1186/s12863-020-00916-5. PMID: 32928120; PMCID: PMC7491182.

Yue R, Lu C, Sun T, Peng T, Han X, Qi J, Yan S, Tie S. Identification and expression profiling analysis of calmodulin-binding transcription activator genes in maize (Zea mays L.) under abiotic and biotic stresses. Front Plant Sci. 2015 Jul 28;6:576. doi: 10.3389/fpls.2015.00576. PMID: 26284092; PMCID: PMC4516887.