Sugars play important roles in plant growth and development, crop yield and quality, as well as responses to abiotic stresses. Abscisic acid (ABA) is a multifunctional hormone. However, the exact mechanism by which ABA regulates sugar accumulation is largely unknown in plants. Here, we tested the expression profile of several sugar transporter and amylase genes in response to ABA treatment. and were isolated and genetically transformed into apple () to investigate their roles in ABA-induced sugar accumulation. The MdAREB2 transcription factor was found to bind to the promoters of the sugar transporter and amylase genes and activate their expression. Both MdAREB2 and MdSUT2 transgenic plants produced more soluble sugars than controls. Furthermore, MdAREB2 promoted the accumulation of sucrose and soluble sugars in an -dependent manner. Our results demonstrate that the ABA-responsive transcription factor MdAREB2 directly activates the expression of amylase and sugar transporter genes to promote soluble sugar accumulation, suggesting a mechanism by which ABA regulates sugar accumulation in plants.

Chlorogenic acid (CA), is found in high abundance in the leaves of a number of plants and has antibacterial, antiphlogistic, antimutagenic, antioxidant and other biological activities. It reportedly possesses antitumor activity via the induction of apoptosis in chronic myelogenous leukemia (CML) cell lines, including U937 and K562 cells. However, the effects of CA on human acute promyelocytic leukemia (APL) HL‑60 cells remains unknown. In the current study, the ability of CA to cause G0/G1 cycle arrest and induce apoptosis in the treatment of human APL HL‑60 cells was investigated. Following 5 days treatment with 1, 5 and 10 µM CA, cell viability and the effects of CA on the growth of HL‑60 cells were investigated using a growth curve constructed using trypan blue staining. Induction of apoptosis and inhibition of cell proliferation were estimated using Wright's‑Giemsa staining, Hoechst 33342 and propidium iodide (PI) staining, DNA ladder analysis and flow cytometry, following 48 h cell treatment with various doses of CA. The results indicated that the growth of HL‑60 cells reached a plateau phase at 72 h and the proliferation inhibition rate of HL‑60 cells in CA‑treated groups was significantly higher compared with the control, in a time‑ and dose‑dependent manner. However, the level of apoptosis of HL‑60 cells treated with CA markedly increased and formed more apoptotic bodies compared with the cells with no drug treatment, according to the Wright's‑Giemsa staining, Hoechst 33342 and PI staining, respectively. Using DNA ladder analysis and flow cytometry it was shown that a significant characteristic DNA ladder was observed when treated with CA. CA was capable of arresting cell cycle at G0/G1 phase. Apoptosis of HL‑60 cells treated with CA for 48 h was promoted significantly in a dose‑dependent manner, as well as the inhibition of proliferation. The observations revealed that CA inhibits proliferation and induces preprophase apoptosis of HL‑60 cells. Thus, the concentration of 10 µM may be the optimal dose for treatment human acute promyelocytic leukemia.

Phytohormone abscisic acid (ABA) regulates many important processes in plants. It is a major molecule facilitating signal transduction during the abiotic stress response. In this study, an ABA-inducible transcription factor gene, MdAREB2, was identified in apple. Transgenic analysis was performed to characterize its function in ABA sensitivity. Overexpression of the MdAREB2 gene increased ABA sensitivity in the transgenic apple compared with the wild-type (WT) control. In addition, it was found that the protein MdAREB2 was phosphorylated at a novel site Thr in response to ABA. A yeast two-hybridization screen of an apple cDNA library demonstrated that a protein kinase, MdCIPK22, interacted with MdAREB2. Their interaction was further verified with Pull Down and Co-IP assays. A series of transgenic analyses in apple calli and plantlets showed that MdCIPK22 was required for ABA-induced phosphorylation at Thr of the MdAREB2 protein and enhanced its stability and transcriptional activity. Finally, it was found that MdCIPK22 increased ABA sensitivity in an MdAREB2-dependent manner. Our findings indicate a novel phosphorylation site in CIPK-AREB regulatory module for the ABA signalling pathway, which would be helpful for researchers to identify the functions of uncharacterized homologs in the future.

Abscisic acid (ABA) induces anthocyanin biosynthesis in many plant species. However, the molecular mechanism of ABA-regulated anthocyanin biosynthesis remains unclear. As a crucial regulator of ABA signaling, ABSCISIC ACID-INSENSITIVE5 (ABI5) is involved in many aspects of plant growth and development. Nevertheless, whether ABI5 regulates anthocyanin biosynthesis has not been reported. In this study, we found that MdABI5, the homolog of Arabidopsis ABI5, positively regulated ABA-induced anthocyanin biosynthesis in apple. A series of biochemical tests showed that MdABI5 specifically interacts with MdbHLH3, a positive regulator of anthocyanin biosynthesis. MdABI5 enhanced the binding of MdbHLH3 to its target genes MdDFR and MdUF3GT. In addition, MdABI5 directly bound to the promoter of MdbHLH3 to activate its expression. Moreover, MdABI5 acted as an enhancer in the ABA-promoted interaction between MdMYB1 and MdbHLH3. Finally, antisense suppression of MdbHLH3 significantly reduced anthocyanin biosynthesis promoted by MdABI5, indicating that MdABI5-promoted anthocyanin biosynthesis was dependent on MdbHLH3. Taken together, our data suggest that MdABI5 plays a positive role in ABA-induced anthocyanin biosynthesis by modulating the MdbHLH3-MdMYB1 complex. Our work enriches the functional studies of ABI5 and further broadens the regulatory network of ABA-mediated anthocyanin biosynthesis, providing new insights for further study of the transcriptional regulatory mechanisms of anthocyanin biosynthesis.

Melatonin not only plays a major role in the regulation of circadian rhythms, but is also involved in antioxidative defense and immunomodulation. Circulating melatonin levels are derived primarily from the pineal gland while other sources of melatonin have also been reported. Here, we show for the first time that astrocytes from the rat cortex and glioma C6 cell line synthesize melatonin in vitro. In addition, we show the presence of serotonin, the precursor of melatonin and the two key enzymes in the pathway of melatonin synthesis, i.e. N-acetyltransferase and hydroxyndole-O-methyltransferase in the cultured rat cortical astrocytes. Release of melatonin into the culture medium showed no diurnal changes. These point to astrocytes as a local source of melatonin in the rat brain. Its exact physiological function remains a topic for future studies.