Abstract
Calmodulin-binding transcription activator (CAMTA) constitutes one of the most important Ca2+/CaM-regulated transcription factor families in plants. Nevertheless, the phylogeny, protein interaction network, and role in nonhost resistance of plant CAMTAs are not well understood. In this study, 200 CAMTA genes were identified from 35 species representing four major plant lineages. The CAMTA genes were conserved in multicellular land plants but absent in unicellular eukaryotes, and were likely to emerge from the fusion of two separate genes encoding a CAMTA-like protein and an IQ/CaM binding motif containing protein, respectively, in the embryophyta lineage ancestor. Approximately one fourth of plant CAMTAs did not contain a TIG domain. This non-TIG class of CAMTAs seems to have newly evolved through mutation of some key amino acids in the TIG domain of flowering land plants after divergence from the non-flowering plants. Phylogenetic analysis classified CAMTA proteins into three major groups and nine distinct subgroups, a result supported by protein domain and motif conservation analyses. Most (59.0 and 21.5%) of the identified CAMTA genes contained 12 or 11 introns, respectively. Gene duplication, intron invasion, enlargement and turnover, as well as exon rearrangements and skipping have apparently occurred during evolution of the CAMTA family. Moreover, 38 potential interactors of six Arabidopsis CAMTAs were predicted and 10 predicted target genes of AtCAMTA3 exhibited changes in expression between Atcamta3 mutants and wild-type plants. The majority of predicted interactors are transcription factors and/or Ca2+/CaM-regulated proteins, suggesting that transcriptional regulation of the target genes might be the dominant functional mechanism of AtCAMTAs, and AtCAMTAs might act together with other Ca2+ signaling components to regulate Ca2+-related biological processes. Furthermore, functional analyses employing Atcamta mutants revealed that AtCAMTA3 negatively regulated the immunity triggered by flg22 and nonhost resistance to Xanthomonas oryzae pv. oryzae via repressing accumulation of reactive oxygen species probably by targeting CBP60G, EDS1, and NDR1 and involving SA pathway.
Highlights
Calcium is a universal secondary messenger used by plants to coordinate their responses to a wide range of biotic and abiotic stresses (Reddy et al, 2011)
Based on domain composition analyses of sequences retrieved from BLAST search using Arabidopsis Calmodulin-binding transcription activator (CAMTA) as query, 200 CAMTA sequences were identified from 35 plant species, including one moss, one lycophyte, six monocots, and 27 eudicots (Figure 1 and Table S1)
These results demonstrate that the CAMTA family is universally present in multicellular land plants but absent in unicellular eukaryotes and CAMTA genes may have evolved before the transition from non-vascular to vascular land plants
Summary
Calcium is a universal secondary messenger used by plants to coordinate their responses to a wide range of biotic and abiotic stresses (Reddy et al, 2011). Follow-up studies showed that CAMTAs belong to a conserved transcription factor (TF) family that exists in all the examined multicellular eukaryotes (Reddy et al, 2000; Bouché et al, 2002; Yang and Poovaiah, 2002; Finkler et al, 2007) This family of TFs possesses multiple domains generally including a CG-1 domain, a TIG domain, an ankyrin (ANK) repeat domain, an IQ domain, and a CaM binding (CaMB) domain that are located in turn from the N terminus to the C terminus. How universal this non-TIG type of CAMTAs exists remains unknown
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