Abstract
Plant carotenoid cleavage oxygenase (CCO) is an enzyme that catalyzes the synthesis of carotenoids and participates in many important physiological functions. The plant CCOs exist in two forms, namely carotenoid cleavage dioxygenase (CCD) and nine-cis epoxide carotenoid dioxygenase (NCED). Although studies have shown that this gene family has been identified in many species, such as Arabidopsis, grape, and tomato, the evolutionary origin of the CCO family and the expression pattern of pepper genes in response to H2O2 and other abiotic stresses are still unclear. In this study, we used the bioinformatics method to identify and analyze the members of the CCO gene family from pepper and other 13 plants from lower to higher plant species based on the whole genome sequence. A total of 158 CCO genes were identified in different plant species and further divided into two groups (e.g., groups I and II). The former was subdivided into CCD7 and CCD8 and have independent evolutionary origins, respectively, while the latter was subdivided into CCD1, CCD4, CCD-like, and NCED, which may have come from a common ancestor. In addition, the results of RNA-seq showed that the expression patterns of pepper CaCCO genes were different in the tissues tested, and only few genes were expressed at high levels such as CaCCD1a, CaCCD4a, CaNCED3, and CaCCD1b. For hydrogen peroxide (H2O2) and other abiotic stresses, such as plant hormones, heat, cold, drought, and NaCl treatments, induction of about half of the CaCCO genes was observed. Moreover, the expression patterns of CaCCOs were further investigated under heat, cold, drought, and NaCl treatments using quantitative real-time PCR (qRT-PCR), and most members were responsive to these stresses, especially some CaCCOs with significant expression changes were identified, such as CaCCD4c, CaCCD-like1, CaCCD8, and CaCCD1b, suggesting the important roles of CaCCOs in abiotic stress responses. All these results will provide a valuable analytical basis for understanding the evolution and functions of the CCO family in plants.
Highlights
As is known to all, due to the global climate change, plant resources and genetic diversity as well as the world food security has had a certain impact, so environmental stress has become the focus of attention of people (Raza et al, 2020)
The results showed that a total of 158 candidate carotenoid cleavage oxygenase (CCO) genes were identified in various plant species, each with a distinct number of variants
The results showed that at least four genes were significantly induced under different stresses, and these genes have similar expression patterns, such as CaCCD1a, CaCCD4a, CaNCED3, CaCCD1b, and CaCCD8
Summary
As is known to all, due to the global climate change, plant resources and genetic diversity as well as the world food security has had a certain impact, so environmental stress has become the focus of attention of people (Raza et al, 2020). Plants are often subjected to various environmental stresses during their life, such as drought, high salt, high temperature, or invasion of pathogenic bacteria. These abiotic stresses or biotic stresses will have a certain impact on the growth and development of plants (Roychoudhury et al, 2013). Carotenoids are important lipid-soluble compounds, contain a large family over 700 types of structures (Britton et al, 2004), and perform a series of important biotic and abiotic stress functions. Plant CCOs are a class of dioxygenases that catalyze the cleavage of carotenoids and their conjugate double bonds in plants. The CCOs can be further divided into nine-cis-epoxide carotenoid dioxygenase (NCED) and carotenoid cleavage dioxygenase (CCDs), based on their substrate informing an epoxy structure (Tan et al, 2003; Auldridge et al, 2006)
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