Identification and genes expression analysis of ATP-dependent phosphofructokinase family members among three Saccharum species.

Sugarcane contributes ~80% of sugar production in the world and is an established biofuel crop. In working towards understanding the molecular basis of high sucrose accumulation, we have annotated and analysed the ATP-dependent phosphofructokinase (PFK) gene family that catalyses the phosphorylation of D-fructose 6-phosphate to D-fructose 1,6-bisphosphate. PFKs play an essential role in sucrose metabolism in plants and their expression patterns are unknown in sugarcane. In this study, based on the sorghum genome and sugarcane EST database, 10 PFK gene members were annotated and further verified by PCR using sugarcane genomic DNA. An unrooted phylogenetic tree was constructed with the deduced protein sequences of PFKs that were from the assembly of cDNA library of sugarcane and other plants. The results showed that gene duplication events and the retention rate after genome wide or segmental duplications occurred in higher frequency in monocots than in dicots and the genes in subgroup II of group III were likely originated from recent duplication events. Quantitative RT-PCR was performed to investigate the gene expression of 10 PFK genes in five tissues of three Saccharum species, including two developmental stages in leaves and three in culms. Of the PFK family members in sugarcane, ScPFK6, 7 and 8 appeared to be the primary isoforms based on the highly abundant expression of these three genes. ScPFK7 showed high expression level in the leaves, suggesting a potential role in sucrose metabolism. ScPFK8 had lower expression level in Saccharum officinarum L. than in the other two species, suggesting negative regulation of sucrose metabolism, which might have contributed to the high sugar content of S. officinarum. The genes in monocot specific subgroup II of group III, PFK7, 8 and 9, showed variation among the three Saccharum species, suggesting potential functional redundancy. Our results provide detailed annotation and analysis of the PFK gene family in sugarcane. Further elucidation of the role of ScPFK8 in the domestication process of sugarcane would be useful.