Abstract
As Ca2+ sensors and effectors, calcium-dependent protein kinases (CDPKs) play important roles in plant growth, development, and response to environmental cues. However, no CDPKs have been characterized in Capsicum annuum thus far. Herein, a genome wide comprehensive analysis of genes encoding CDPKs and CDPK-related protein kinases (CRKs) was performed in pepper, a total of 31 CDPK genes and five closely related kinase genes were identified, which were phylogenetically divided into four distinct subfamilies and unevenly distributed across nine chromosomes. Conserved sequence and exon-intron structures were found to be shared by pepper CDPKs within the same subfamily, and the expansion of the CDPK family in pepper was found to be due to segmental duplication events. Five CDPKs in the C. annuum variety CM334 were found to be mutated in the Chiltepin variety, and one CDPK present in CM334 was lost in Chiltepin. The majority of CDPK and CRK genes were expressed in different pepper tissues and developmental stages, and 10, 12, and 8 CDPK genes were transcriptionally modified by salt, heat, and Ralstonia solanacearum stresses, respectively. Furthermore, these genes were found to respond specifically to one stress as well as respond synergistically to two stresses or three stresses, suggesting that these CDPK genes might be involved in the specific or synergistic response of pepper to salt, heat, and R. solanacearum. Our results lay the foundation for future functional characterization of pepper CDPK and its closely related gene families.
Highlights
In their natural habitat, plants frequently encounter different abiotic and biotic stresses, and have evolved a complicated defense system to defend themselves against such stresses
The results showed that most of the high temperature-responsive calcium-dependent protein kinases (CDPKs) genes were upregulated in response to high temperature treatment; the transcripts of CaCDPK18, CaCDPK20, and CaCDPK21 decreased at 2–6 hpt and increased at 12–24 hpt, CaCRK4, and CaCRK5 were downregulated in response to high temperature treatment, suggesting that these CDPK genes are involved in the response of pepper to high temperature, acting as positive or negative regulators
Like CDPK genes in other plants such as cotton and maize (Ferreira Neto et al, 2013; Zuo et al, 2013; Liu et al, 2014), the 31 CDPK genes and the five CDPK-related protein kinases (CRKs) genes identified in pepper genome are unevenly distribute on different chromosomes
Summary
Plants frequently encounter different abiotic and biotic stresses, and have evolved a complicated defense system to defend themselves against such stresses. CDPKs expression in Capsicum annuum concentration with varying frequency, amplitude, and duration dependent on the stress cues These calcium concentration changes are sensed and decoded by different Ca2+ sensors/Ca2+-binding proteins, including calmodulins (CaMs), calmodulin-like proteins (CaMLs), calcineurin Blike proteins (CBLs), and calcium-dependent protein kinases (CDPKs), which subsequently result in different downstream defense responses. The large family of CDPKs is characterized by an N-variable domain, a protein kinase domain, an autoinhibitory domain, and a CaM-like domain (Cheng et al, 2002). These unique features enable CDPKs to function as Ca2+ sensors and effectors and to play important roles in regulating the downstream components of calcium signaling. The signaling pathways mediated by CDPKs appear to be complicated—for example, crosstalk between the CDPK and MAPK signaling pathways has been found (Wurzinger et al, 2011; Ding et al, 2013)—and the underlying mechanism of the biological processes regulated by CDPK genes remains to be elucidated
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