Two low-molecular-weight polysaccharides (GLP-1 and GLP-2) were purified from Ganoderma leucocontextum fruiting bodies, and their physicochemical properties and antioxidant activities were investigated and compared in this study. The results showed that GLP-1 and GLP-2 were mainly composed of mannose, glucose, galactose, xylose, and arabinose, with weight-average molecular weights of 6.31 and 14.07 kDa, respectively. Additionally, GLP-1 and GLP-2 had a similar chain conformation, crystal structure, and molecular surface morphology. Moreover, GLP-1 exhibited stronger antioxidant activities than GLP-2 in five different assays: 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), hydroxyl radical, superoxide anion radical, ferric reducing antioxidant power (FRAP), and oxygen radical antioxidant capacity (ORAC). The main linkage types of GLP-1 were found to be →4)-α-D-Glcp-(1→, →4)-β-D-Glcp-(1→, →3)-β-D-Glcp-(1→, →6)-β-D-Galp-(1→, →6)-α-D-Glcp-(1→, →4,6)-α-D-Glcp-(1→, and Glcp-(1→ by methylation analysis and nuclear magnetic resonance (NMR) spectroscopy. In addition, GLP-1 could protect NIH3T3 cells against tert-butyl hydroperoxide (tBHP)-induced oxidative damage by increasing catalase (CAT) and glutathione peroxidase (GSH-Px) activities, elevating the glutathione/oxidized glutathione (GSH/GSSG) ratio, and decreasing the malondialdehyde (MDA) level. These findings indicated that GLP-1 could be explored as a potential antioxidant agent for application in functional foods.

Caffeine is an important functional substance and is abundant in tea plant, but little is known about how its biosynthesis is regulated by transcription factors. In this study, the NAC-like transcription factor-encoding gene CsNAC7, which is involved in caffeine synthesis, was isolated from a Yinghong 9 cDNA library using a yeast one-hybrid assay; this gene comprises 1371 bp nucleotides and is predicted to encode 456 amino acids. The expression of CsNAC7 at the transcriptional level in tea shoots shared a similar pattern with that of the caffeine synthase gene yhNMT1 in the spring and summer, and its expressed protein was localized in the nucleus. Assays of gene activity showed that CsNAC7 has self-activation activity in yeast, that the active region is at the N-terminus, and that the transient expression of CsNAC7 could significantly promote the expression of yhNMT1 in tobacco leaves. In addition, overexpression or silencing of CsNAC7 significantly increased or decreased the expression of yhNMT1 and the accumulation of caffeine in transgenic tea calli, respectively. Our data suggest that the isolated transcription factor CsNAC7 positively regulates the caffeine synthase gene yhNMT1 and promotes caffeine accumulation in tea plant.