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Identification, Expression, and Functional Analysis of the Fructokinase Gene Family in Cassava.

ABSTRACT: Fructokinase (FRK) proteins play important roles in catalyzing fructose phosphorylation and participate in the carbohydrate metabolism of storage organs in plants. To investigate the roles of FRKs in cassava tuber root development, seven FRK genes (MeFRK1-7) were identified, and MeFRK1-6 were isolated. Phylogenetic analysis revealed that the MeFRK family genes can be divided into α (MeFRK1, 2, 6, 7) and β (MeFRK3, 4, 5) groups. All the MeFRK proteins have typical conserved regions and substrate binding residues similar to those of the FRKs. The overall predicted three-dimensional structures of MeFRK1-6 were similar, folding into a catalytic domain and a β-sheet ''lid" region, forming a substrate binding cleft, which contains many residues involved in the binding to fructose. The gene and the predicted three-dimensional structures of MeFRK3 and MeFRK4 were the most similar. MeFRK1-6 displayed different expression patterns across different tissues, including leaves, stems, tuber roots, flowers, and fruits. In tuber roots, the expressions of MeFRK3 and MeFRK4 were much higher compared to those of the other genes. Notably, the expression of MeFRK3 and MeFRK4 as well as the enzymatic activity of FRK were higher at the initial and early expanding tuber stages and were lower at the later expanding and mature tuber stages. The FRK activity of MeFRK3 and MeFRK4 was identified by the functional complementation of triple mutant yeast cells that were unable to phosphorylate either glucose or fructose. The gene expression and enzymatic activity of MeFRK3 and MeFRK4 suggest that they might be the main enzymes in fructose phosphorylation for regulating the formation of tuber roots and starch accumulation at the tuber root initial and expanding stages.

SUBMITTER: Yao Y

PROVIDER: S-EPMC5713366 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Sugarcane is an important sugar crop contributing up to about 80% of the world sugar production. Efforts to characterize the genes involved in sugar metabolism at the molecular level are growing since increasing sugar content is a major goal in the breeding of new sugarcane varieties. Fructokinases (FRK) are the main fructose phosphorylating enzymes with high substrate specificity and affinity.In this study, by combining comparative genomics approaches with BAC resources, seven fructokinase genes were identified in S. spontaneum. Phylogenetic analysis based on representative monocotyledon and dicotyledon plant species suggested that the FRK gene family is ancient and its evolutionary history can be traced in duplicated descending order: SsFRK4, SsFRK6/SsFRK7,SsFRK5, SsFRK3 and SsFRK1/SsFRK2. Among the close orthologs, the number and position of exons in FRKs were conserved; in contrast, the size of introns varied among the paralogous FRKs in Saccharum. Genomic constraints were analyzed within the gene alleles and between S. spontaneum and Sorghum bicolor, and gene expression analysis was performed under drought stress and with exogenous applications of plant hormones. FRK1, which was under strong functional constraint selection, was conserved among the gene allelic haplotypes, and displayed dominant expression levels among the gene families in the control conditions, suggesting that FRK1 plays a major role in the phosphorylation of fructose. FRK3 and FRK5 were dramatically induced under drought stress, and FRK5 was also found to increase its expression levels in the mature stage of Saccharum. Similarly, FRK3 and FRK5 were induced in response to drought stress in Saccharum. FRK2 and FRK7 displayed lower expression levels than the other FRK family members; FRK2 was under strong genomic selection constraints whereas FRK7 was under neutral selection. FRK7 may have become functionally redundant in Saccharum through pseudogenization. FRK4 and FRK6 shared the most similar expression pattern: FRK4 was revealed to have higher expression levels in mature tissues than in premature tissues of Saccharum, and FRK6 presented a slight increase under drought stress.Our study presents a comprehensive genomic study of the entire FRK gene family in Saccharum, providing the foundations for approaches to characterize the molecular mechanism regulated by the SsFRK family in sugarcane.

Project description:NAC [no apical meristem (NAM), Arabidopsis transcription activation factor [ATAF1/2] and cup-shaped cotyledon (CUC2)] proteins is one of the largest groups of plant specific transcription factors and plays a crucial role in plant growth, development, and adaption to the environment. Currently, no information is known about the NAC family in cassava. In this study, 96 NAC genes (MeNACs) were identified from the cassava genome. Phylogenetic analysis of the NACs from cassava and Arabidopsis showed that MeNAC proteins can be clustered into 16 subgroups. Gene structure analysis found that the number of introns of MeNAC genes varied from 0 to 5, with the majority of MeNAC genes containing two introns, indicating a small gene structure diversity of cassava NAC genes. Conserved motif analysis revealed that all of the identified MeNACs had the conserved NAC domain and/or NAM domain. Global expression analysis suggested that MeNAC genes exhibited different expression profiles in different tissues between wild subspecies and cultivated varieties, indicating their involvement in the functional diversity of different accessions. Transcriptome analysis demonstrated that MeNACs had a widely transcriptional response to drought stress and that they had differential expression profiles in different accessions, implying their contribution to drought stress resistance in cassava. Finally, the expression of twelve MeNAC genes was analyzed under osmotic, salt, cold, ABA, and H2O2 treatments, indicating that cassava NACs may represent convergence points of different signaling pathways. Taken together, this work found some excellent tissue-specific and abiotic stress-responsive candidate MeNAC genes, which would provide a solid foundation for functional investigation of the NAC family, crop improvement and improved understanding of signal transduction in plants. These data bring new insight on the complexity of the transcriptional control of MeNAC genes and support the hypothesis that NACs play an important role in plant growth, development, and adaption of environment.

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Identification, Expression, and Functional Analysis of the Fructokinase Gene Family in Cassava.

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