The Evolution And Gene Function Of Fructokinase In Saccharum

Sugarcane is a major crop in tropical and subtropical regions worldwide for producing sugarand biofuel. However, since all Saccharum species and varieties are high polyploidy, assembling a reference sugarcane genome may not be possible in the short run because of the computational and logistic challenge when sequencing the sugarcane genome. Due to the lack of whole genome sequence, less is known about gene families involved in sugar (photoasimilate) metabolism in sugarcane, including the fructokinase (FRK), which is of primary importance in phosphorylation of fructose in plants.In this study, the FRK gene sequences from sorghum, which share high similarity with sugarcane, were used as query sequences for BLASTN searches against the sequenced BAC libraries data sets. The seven S. spontaneum FRK genes identified in our study were designed as SsFRK1 to SsFRK7. Gene structure and allelic haplotype comparative analysis were performed on those genes. To explore the evolutionary relationships between different plant FRK homologues, we constructed a phylogenetic tree using 71 FRK genes from 8 species (dicots:Vitis vinifera, Arabidopsis thaliana, Lycopersicon esculentum, Solanum tuberosum; monocots:Oryza sativa, Zea mays, Saccharum spontaneum, Sorghum bicolor) and graphed the gene structure using GSDS. The phylogenetic analysis showed that the FRK gene family is an evolutionally conserved group of genes existing before the divergence of dicot and monocot.To investagate the expression pattern of SsFRK genes, we performed comparative transcriptome profiling among three Saccharum species and sugarcane hybrid at different developmental stages of seedling with hormone treatment or not and from five different tissues of the mature plants. The results showed FRK1 and FRK5 had predominant expression in Saccharum FRK families. The expression patterns of Saccharum FRK genes differed under different developmental stages and treatment.Arabidopsis mutants were used to investigate the potential physiological functions of sugarcane FRK genes. Based on the phenotype of the T-DNA insertion mutants of Arabidopsis, we found that the mutant transferred with SsFRK1 had shortened root and those transferred with SsFRK5 showed longer stem compared with wild type. Further functional characterization of Saccharum FRK genes is required to understand the precise roles in sugar metabolism.