A novel glutathione S-transferase gene from sweetpotato, IbGSTF4, is involved in anthocyanin sequestration.

Anthocyanins are synthesized by multi-enzyme complexes localized at the cytoplasmic surface of the endoplasmic reticulum (synthesis site), and transported to the destination site, the vacuole. Three mechanisms for the vacuolar accumulation of anthocyanin in plant species have been proposed. Previous studies have indicated that glutathione S-transferase (GST) genes from model and ornamental plants are involved in anthocyanin transportation. In the present study, an anthocyanin-related GST, IbGSTF4, was identified and characterized based on transcriptome results. Phylogenetic analysis revealed that IbGSTF4 was most closely correlated to PhAN9 and CkmGST3, the anthocyanin-related GST of Petunia hybrida and Cyclamen. Furthermore, the expression analysis revealed that IbGSTF4 is strongly expressed in pigmented tissues, when compared to green organs, which is in agreement to the ability to correlate with anthocyanin accumulation. A GST activity assay uncovered that the IbGST4 protein owned similar activities with the GST family. Furthermore, the molecular functional complementation of Arabidopsis thaliana mutant tt19 demonstrated that IbGSTF4 might play a vital role in the vacuole sequestration of anthocyanin in sweetpotato. Moreover, the dual luciferase assay revealed that the LUC driven by the promoter of IbGSTF4 could not be directly activated by IbMYB1, suggesting that the regulatory mechanism of anthocyanin accumulation and sequestration in sweetpotato was intricate.

Cloning and characterization of a novel GIGANTEA gene in sweet potato.

The transition from vegetative to reproductive growth, a key event in the lifecycle of a plant, is affected by environmental stresses. The flowering-time regulator GIGANTEA (GI) may be contributing to susceptibility of the regulation of photoperiodic flowering, circadian rhythm control, and abiotic stress resistance in Arabidopsis. However, the role of GI in sweet potato remains unknown. Here, we isolated and characterized a GI gene (IbGI) from sweet potato (Ipomoea batatas [L.] Lam). The IbGI cDNA sequence was isolated based on information from a sweet potato transcriptome database. IbGI mRNA transcript levels showed robust circadian rhythm control during the light-dark transition, and the expression of IbGI was stronger in leaves and roots than in stems. IbGI protein is predominantly localized to the nucleus. IbGI expression was upregulated by high temperature, drought, and salt stress but downregulated by cold stress. Overexpressing IbGI in the Arabidopsis gi-2 mutant background rescued its late flowering phenotype and reduced its salt tolerance. Taken together, these results indicate that IbGI shares functions in regulating flowering, the circadian rhythm, and tolerance to some stresses with other GI orthologs.