Phylogenetic relationships of sucrose transporters (SUTs) in plants and genome-wide characterization of SUT genes in Orchidaceae reveal roles in floral organ development

Sucrose is the primary form of photosynthetically produced carbohydrates transported long distance in many plant species and substantially affects plant growth, development and physiology. Sucrose transporters (SUTs or SUCs) are a group of membrane proteins that play vital roles in mediating sucrose allocation within cells and at the whole-plant level. In this study, we investigated the relationships among SUTs in 24 representative plant species and performed an analysis of SUT genes in three sequenced Orchidaceae species: Dendrobium officinale, Phalaenopsis equestris, and Apostasia shenzhenica. All the SUTs from the 24 plant species were classified into three groups and five subgroups, subgroups A, B1, B2.1, B2.2, and C, based on their evolutionary relationships. A total of 22 SUT genes were identified among Orchidaceae species, among which D. officinale had 8 genes (DoSUT01-08), P. equestris had eight genes (PeqSUT01-08) and A. shenzhenica had 6 genes (AsSUT01-06). For the 22 OrchidaceaeSUTs, subgroups A, B2.2 and C contained three genes, whereas the SUT genes were found to have significantly expanded in the monocot-specific subgroup B2.1, which contained 12 genes. To understand sucrose partitioning and the functions of sucrose transporters in Orchidaceae species, we analyzed the water-soluble sugar content and performed RNA sequencing of different tissues of D. officinale, including leaves, stems, flowers and roots. The results showed that although the total content of water-soluble polysaccharides was highest in the stems of D. officinale, the sucrose content was highest in the flowers. Moreover, gene expression analysis showed that most of the DoSUTs were expressed in the flowers, among which DoSUT01,DoSUT07 and DoSUT06 had significantly increased expression levels. These results indicated that stems are used as the main storage sinks for photosynthetically produced sugar in D. officinale and that DoSUTs mainly function in the cellular machinery and development of floral organs. Our findings provide valuable information on sucrose partitioning and the evolution and functions of SUT genes in Orchidaceae and other species.

Phylogenetic Relationships of Sucrose Transporters (SUTs) in Plants and Genome-wide Characterization of SUT Genes in Orchidaceae

BackgroundSucrose is the primary form of photosynthetically produced carbohydrates transported long distance in many plant species, which significantly affects plant growth, development and physiology. Sucrose transporters (SUTs or SUCs) are a group of membrane proteins that play vital roles in mediating sucrose allocation within cells and at the whole plant level.ResultsIn this study, we investigated the relationship of SUTs in 24 representative plant species and performed a comprehensive analysis of SUT genes in three sequenced Orchidaceae species, Dendrobium officinale, Phalaenopsis equestris, and Apostasia shenzhenica. All the SUTs from 24 plants were classified into three groups and five subgroups: subgroups A, B1, B2.1, B2.2, and C, based on the evolutionary relationships. A total of 22 SUT genes were identified in Orchidaceae species, among which D. officinale had 8 genes (DenSUT01-08), P. equestris had 8 genes (PeqSUT01-08) and A. shenzhenica had 6 genes (PeqSUT01-06). For the 22 Orchidaceae SUTs, each of the subgroups A, B2.2 and C contains three genes, whereas the SUT genes were significantly expanded in the monocot-specific subgroup B2.1 which contained 12 genes. To shed light into sucrose partitioning and functions of sucrose transporters in Orchidacea species, we analysed water-soluble sugar content and performed RNA sequencing of different tissues of D. officinale, including leaves, stems, flowers and roots. The results showed that although total content of water-soluble polysaccharides was highest in the stems of D. officinale, the sucrose content was highest in flowers. Moreover, gene expression analysis showed that most of the DenSUTs were expressed in flowers, among which DenSUT01, DenSUT07 and DenSUT06 had significantly high expression levels.ConclusionsThese results indicated that stems are used as main storage sinks for photosynthetically produced sugar in D. officinale, and that the DenSUTs mainly take functions in the cellular machinery and development of floral organs. Our findings provide valuable information on sucrose partitioning and the evolution and functions of SUT genes in Orchidaceae and other species.