Investigation into the Expression of Sucrose Transporters and Sucrose Phosphate Synthase mRNA in Different Plant Species

Assimilate partitioning is an important and highly integrated process in higher plants which involves not only transport of sugars from source to sink organs but also the regulation of genes triggered by sugars. In this study, we investigated the transcripts level of sucrose transporters (ShSUT1A and ShSUT4) and sucrose phosphate synthase (SPS) mRNA expression in different plant species. RT-PCR analyses showed that ShSUT1A and ShSUT4 accumulated abundantly in sugarcane tissues. In other plant species, ShSUT1A expressed predominantly in maize ( Zea mays L.) leaves with low expression in Arabidopsis thaliana and Arabidopsis hallari shoots and roots. ShSUT4 expressed strongly in sugarcane tissues, but, it was not detected in the other plant species. SPS, considered a key enzyme in regulation of sucrose biosynthesis in plants, was highly expressed in sugarcane as compared with maize, but it was not expressed or detected in Arabidopsis . Phylogenetic analysis of 51 plant sucrose transporters fall into two clearly separable groups: Group I and Group II. ShSUT1A shared 67 % identity with ZmSUT1 and was still able to show high SUT expression in maize. The similarity between the cereal SUT1 group and the dicot SUT2 group appears also to extend to gene structure. This high level of conservation of gene structure is intriguing, considering the diverse functions for these proteins. The phylogenetic analysis of SPS revealed that sugarcane and maize assembled into unique subgroup within group III with 95 % identity, while Arabidopsis was in a separate small subgroup, group I with 70 % identity.