Abstract
Sugar transporter protein (STP) genes are involved in multiple biological processes, such as plant responses to various stresses. However, systematic analysis and functional information of STP family genes in Brassica oleracea are very limited. A comprehensive analysis was carried out to identify BoSTP genes and dissect their phylogenetic relationships and to investigate the expression profiles in different organs and in response to the clubroot disease. A total of 22 BoSTP genes were identified in the B. oleracea genome and they were further classified into four clades based on the phylogenetic analysis. All the BoSTP proteins harbored the conserved sugar transporter (Sugar_tr, PF00083) domain, and the majority of them contained 12 transmembrane helices (TMHs). Rates of synonymous substitution in B. oleracea relative to Arabidopsis thaliana indicated that STP genes of B. oleracea diverged from those of A. thaliana approximately 16.3 million years ago. Expression profiles of the BoSTP genes in different organs derived from RNA-Seq data indicated that a large number of the BoSTP genes were expressed in specific organs. Additionally, the expression of BoSTP4b and BoSTP12 genes were induced in roots of the clubroot-susceptible cabbage (CS-JF1) at 28 days after inoculation with Plasmodiophora brassicae, compared with mock-inoculated plants. We speculated that the two BoSTPs might be involved in monosaccharide unloading and carbon partitioning associated with P. brassicae colonization in CS-JF1. Subcellular localization analysis indicated that the two BoSTP proteins were localized in the cell membrane. This study provides insights into the evolution and potential functions of BoSTPs.
Highlights
IntroductionSugars (e.g., monosaccharides, sucrose, and polyols) act as carbohydrate molecules, main energy sources, precursors of cellular compounds, and signaling molecules for signal transduction as well as environmental stress responses, which are important for plant growth and development [1,2,3,4]
Sugars act as carbohydrate molecules, main energy sources, precursors of cellular compounds, and signaling molecules for signal transduction as well as environmental stress responses, which are important for plant growth and development [1,2,3,4]
Phylogenetic analysis revealed that these Sugar transporter protein (STP) proteins could be divided into four distinct clades (I–IV), and the BoSTPs were grouped with AtSTPs and BoSTPs in each clade
Summary
Sugars (e.g., monosaccharides, sucrose, and polyols) act as carbohydrate molecules, main energy sources, precursors of cellular compounds, and signaling molecules for signal transduction as well as environmental stress responses, which are important for plant growth and development [1,2,3,4]. Sugar transport is mediated by monosaccharide transporters (MSTs) and sucrose transporters (SUTs) and sugars will eventually be exported transporters (SWEETs) [7,8]. The sucrose can be transported from the phloem to sink cells via a symplastic pathway or an apoplastic pathway [6]. Genes 2019, 10, 71 sucrose, the transport of glucose and fructose, which are hydrolyzed from the sucrose in the apoplast, is regulated by sugar transporter proteins (STPs) and hexose transporters (HTs) [9,10]. Sugar transporter proteins, belonging to the MST superfamily, commonly contain 12 transmembrane helices (TMHs) and are localized in the cell membrane [11]. Sugar transporter proteins are regarded as H+ /sugar symporters and can transport fructose, glucose, galactose, mannose, and xylose [12]
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