Abstract
Trehalose-6-phosphate synthase (TPS) plays important roles in trehalose metabolism and signaling. Plant TPS proteins contain both a TPS and a trehalose-6-phosphate phosphatase (TPP) domain, which are coded by a multi-gene family. The plant TPS gene family has been divided into class I and class II. A previous study showed that the Populus, Arabidopsis, and rice genomes have seven class I and 27 class II TPS genes. In this study, we found that all class I TPS genes had 16 introns within the protein-coding region, whereas class II TPS genes had two introns. A significant sequence difference between the two classes of TPS proteins was observed by pairwise sequence comparisons of the 34 TPS proteins. A phylogenetic analysis revealed that at least seven TPS genes were present in the monocot–dicot common ancestor. Segmental duplications contributed significantly to the expansion of this gene family. At least five and three TPS genes were created by segmental duplication events in the Populus and rice genomes, respectively. Both the TPS and TPP domains of 34 TPS genes have evolved under purifying selection, but the selective constraint on the TPP domain was more relaxed than that on the TPS domain. Among 34 TPS genes from Populus, Arabidopsis, and rice, four class I TPS genes (AtTPS1, OsTPS1, PtTPS1, and PtTPS2) were under stronger purifying selection, whereas three Arabidopsis class I TPS genes (AtTPS2, 3, and 4) apparently evolved under relaxed selective constraint. Additionally, a reverse transcription polymerase chain reaction analysis showed the expression divergence of the TPS gene family in Populus, Arabidopsis, and rice under normal growth conditions and in response to stressors. Our findings provide new insights into the mechanisms of gene family expansion and functional evolution.
Highlights
Trehalose (a-D-glucopyranosyl a-D-glucopyranoside) is a nonreducing disaccharide in which two glucose units are linked in an a,a-1,1-glycosidic linkage
(1) Which genetic mechanisms contribute to the expansion of this gene family? (2) Do the trehalose-6-phosphate synthase (TPS) and trehalose-6phosphate phosphatase (TPP) domains of TPS genes undergo similar selection pressure? (3) Which factors drive the functional divergence of class I and class II TPS genes? In order to address these questions, in this study, we examined the evolutionary characterisation of the TPS gene family in Populus, Arabidopsis, and rice
Our molecular evolution analysis revealed that the TPS domains of four class I TPS genes (AtTPS1, OsTPS1, PtTPS1, and PtTPS2) among 34 TPS genes from Populus, Arabidopsis, and rice, were under stronger purifying selection, indicating functional conservation of the TPS domain among the four TPS genes
Summary
Trehalose (a-D-glucopyranosyl a-D-glucopyranoside) is a nonreducing disaccharide in which two glucose units are linked in an a,a-1,1-glycosidic linkage. Trehalose plays important roles in protecting plants from heat, cold, and osmotic and dehydration stress [1,2,3,4]. The biosynthesis of plant trehalose consists of two enzymatic steps. Trehalose-6-phosphate synthase (TPS) catalyses the transfer of glucose from UDP-glucose to glucose 6phosphate (G6P) to produce trehalose-6-phosphate (T6P). T6P is dephosphorylated into trehalose by trehalose-6phosphate phosphatase (TPP). The plant TPS proteins contain the TPS and TPP domains, whereas TPP proteins contain only TPP domains. Plant TPP proteins have TPP activities [5]. Plant TPS proteins contain TPP domains, many studies have not detected TPP activity [6,7]. The TPP domains in plant TPS proteins appear to have lost enzymatic activity during evolution. The evolutionary basis of this loss is not yet understood
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