Identification and relative expression analysis of CaFRK gene family in pepper

Fructokinase is the main catalytic enzyme for fructose phosphorylation and can also act as a glucose receptor and signal molecule to regulate the metabolism of plants, which plays an important role in plant growth and development. In this study, the CaFRK gene family and their molecular characteristics are systematically identified and analyzed, and the specific expression of CaFRKs under different tissues, abiotic stresses and hormone treatments were explored. Nine FRK genes were authenticated in pepper genome database, which were dispersedly distributed on eight reference chromosomes and predicted to localize in the cytoplasm. Many cis-acting elements that respond to light, different stresses, hormones and tissue-specific expression were found in the promoters of CaFRKs. FRK proteins of four species including Capsicum annuum, Arabidopsis thaliana, Solanum lycopersicum and Oryza sativa were divided into four groups via phylogenetic analysis. The collinearity analysis showed that there were two collinear gene pairs between CaFRKs and AtFRKs. In addition, it was significantly found that CaFRK9 expressed far higher in flower than other tissues, and the relative expression of CaFRK9 was gradually enhanced with the development of flower buds in fertile accessions, 8B, R1 and F-1. Nevertheless, CaFRK9 hardly expressed in all stages of cytoplasmic male sterile lines. Based on the quantitative real-time PCR, most of CaFRK genes showed significant up-regulation under low-temperature, NaCl and PEG6000 treatments. On the contrary, the expression levels of most CaFRKs revealed a various trend in response to hormone treatments (IAA, ABA, GA(3), SA and MeJA). This study systematically analyzed CaFRK gene family and studied its expression pattern, which lay the foundation of CaFRK genes cloning and functional verification response to abiotic stresses, and provides new insights into exploring the CaFRK genes on the pollen development in pepper.