Abstract
BackgroundSucrose phosphate synthase (SPS) genes play vital roles in sucrose production across various plant species. Modern sugarcane cultivar is derived from the hybridization between the high sugar content species Saccharum officinarum and the high stress tolerance species Saccharum spontaneum, generating one of the most complex genomes among all crops. The genomics of sugarcane SPS remains under-studied despite its profound impact on sugar yield.ResultsIn the present study, 8 and 6 gene sequences for SPS were identified from the BAC libraries of S. officinarum and S. spontaneum, respectively. Phylogenetic analysis showed that SPSD was newly evolved in the lineage of Poaceae species with recently duplicated genes emerging from the SPSA clade. Molecular evolution analysis based on Ka/Ks ratios suggested that polyploidy reduced the selection pressure of SPS genes in Saccharum species. To explore the potential gene functions, the SPS expression patterns were analyzed based on RNA-seq and proteome dataset, and the sugar content was detected using metabolomics analysis. All the SPS members presented the trend of increasing expression in the sink-source transition along the developmental gradient of leaves, suggesting that the SPSs are involved in the photosynthesis in both Saccharum species as their function in dicots. Moreover, SPSs showed the higher expression in S. spontaneum and presented expressional preference between stem (SPSA) and leaf (SPSB) tissue, speculating they might be involved in the differentia of carbohydrate metabolism in these two Saccharum species, which required further verification from experiments.ConclusionsSPSA and SPSB genes presented relatively high expression and differential expression patterns between the two Saccharum species, indicating these two SPSs are important in the formation of regulatory networks and sucrose traits in the two Saccharum species. SPSB was suggested to be a major contributor to the sugar accumulation because it presented the highest expressional level and its expression positively correlated with sugar content. The recently duplicated SPSD2 presented divergent expression levels between the two Saccharum species and the relative protein content levels were highest in stem, supporting the neofunctionalization of the SPSD subfamily in Saccharum.
Highlights
Sucrose phosphate synthase (SPS) genes play vital roles in sucrose production across various plant species
spontaneum and presented expressional preference between stem (SPSA) and SPSB genes presented relatively high expression and differential expression patterns between the two Saccharum species, indicating these two SPSs are important in the formation of regulatory networks and sucrose traits in the two Saccharum species
SPSB was suggested to be a major contributor to the sugar accumulation because it presented the highest expressional level and its expression positively correlated with sugar content
Summary
Sucrose phosphate synthase (SPS) genes play vital roles in sucrose production across various plant species. The following processes are catalyzed by a series of enzymes [4], in which sucrose phosphate synthase (SPS) is one of the most important ones. In addition to the wellrecognized role of SPS in sucrose biosynthesis in source leaves, it is becoming clear that SPS plays an important and key role in heterotrophic cells engaging in the net sucrose degradation [5]. Significant turnover of the endogenous sucrose pool was observed in germinating Ricinus cotyledons [6] This turnover of sucrose is thought to be involved in a futile cycle of simultaneous synthesis and cleavage, resulting from changes in the activation rate of SPS phosphorylation [7]. SPS plays a crucial role in carbohydrate metabolism by regulating the partitioning of carbon between starch production and carbohydrate (sucrose) accumulation in many physiological and developmental processes
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