Abstract
BackgroundCalmodulin (CaM) is a major calcium sensor in all eukaryotes. It binds calcium and modulates the activity of a wide range of downstream proteins in response to calcium signals. However, little is known about the CaM gene family in Solanaceous species, including the economically important species, tomato (Solanum lycopersicum), and the gene silencing model plant, Nicotiana benthamiana. Moreover, the potential function of CaM in plant disease resistance remains largely unclear.ResultsWe performed genome-wide identification of CaM gene families in Solanaceous species. Employing bioinformatics approaches, multiple full-length CaM genes were identified from tomato, N. benthamiana and potato (S. tuberosum) genomes, with tomato having 6 CaM genes, N. benthamiana having 7 CaM genes, and potato having 4 CaM genes. Sequence comparison analyses showed that three tomato genes, SlCaM3/4/5, two potato genes StCaM2/3, and two sets of N. benthamiana genes, NbCaM1/2/3/4 and NbCaM5/6, encode identical CaM proteins, yet the genes contain different intron/exon organization and are located on different chromosomes. Further sequence comparisons and gene structural and phylogenetic analyses reveal that Solanaceous species gained a new group of CaM genes during evolution. These new CaM genes are unusual in that they contain three introns in contrast to only a single intron typical of known CaM genes in plants. The tomato CaM (SlCaM) genes were found to be expressed in all organs. Prediction of cis-acting elements in 5' upstream sequences and expression analyses demonstrated that SlCaM genes have potential to be highly responsive to a variety of biotic and abiotic stimuli. Additionally, silencing of SlCaM2 and SlCaM6 altered expression of a set of signaling and defense-related genes and resulted in significantly lower resistance to Tobacco rattle virus and the oomycete pathogen, Pythium aphanidermatum.ConclusionsThe CaM gene families in the Solanaceous species tomato, N. benthamiana and potato were identified through a genome-wide analysis. All three plant species harbor a small set of genes that encode identical CaM proteins, which may manifest a strategy of plants to retain redundancy or enhanced quantitative gene function. In addition, Solanaceous species have evolved one new group of CaM genes during evolution. CaM genes play important roles in plant disease resistance to a variety of pathogens.
Highlights
Calmodulin (CaM) is a major calcium sensor in all eukaryotes
96 and 81 nonreduntant sequences were retrieved in tomato, potato (S. tuberosum) and Nicotiana benthamiana genomes, respectively
These sequences were aligned with the canonical Arabidopsis CaM (AtCaM2) with CLUSTALX program and viewed by GeneDoc for the sequence identity to AtCaM2
Summary
Calmodulin (CaM) is a major calcium sensor in all eukaryotes. It binds calcium and modulates the activity of a wide range of downstream proteins in response to calcium signals. Calmodulin (CaM) is a major Ca2+ sensor thought to interpret Ca2+ signatures in plants It is a small protein, typically comprising only about 149 amino acids. Genome-wide identification of CaM genes in model plant species, such as Arabidopsis and rice [5,6,7], has revealed that CaM proteins are typically encoded by gene families. Plants may contain several CaM isoforms that differ in only a few amino acids, with one of the isoforms being encoded by several genes located on different chromosomes of the genome. CaMs in many Solanaceous species, including the economically important species tomato and the model species for gene silencing studies, Nicotiana benthamiana, have not yet been identified or characterized. Genome-wide analysis of CaM gene families in other Solanaceous species has not yet been conducted
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