microRNA-9 functions as a tumor suppressor in colorectal cancer by targeting CXCR4.

MicroRNAs (miRs) dysregulation has been proven to play a crucial role in the initiation and progression of colorectal cancer (CRC). miR-9 functions as a tumor suppressor in many cancer types, including CRC. However, the precise role of miR-9 and the underlying molecular mechanisms that miR-9 involves in CRC progression remain largely unknown. In this study, it was reported that miR-9 had lower expression in CRC tissue samples than in those matched adjacent non-tumor tissues. Deregulated miR-9 expression was inverse correlated with the TNM stage, lymph node metastasis, and prognosis of CRC patients. Ectopic miR-9 expression suppressed CRC cell proliferation, migration, and invasion. Dual-Luciferase Reporter Assay confirmed that C-X-C Motif Chemokine Receptor 4 (CXCR4) was a direct miR-9 target, and the effects of miR-9 were mimicked through CXCR4 depletion in vitro. CXCR4 rescue experiments further verified that CXCR4 is a functional target of miR-9. Animal xenograft assays also provided evidence that miR-9 functions as a tumor suppressor via targeting CXCR4 in vivo. Mechanistically, miR-9 overexpression or CXCR4 knockdown influenced cell proliferation and epithelial-mesenchymal transition (EMT). Results suggest that miR-9 acts as a tumor suppressor in CRC progression by regulating CXCR4.

A novel tomato MYC-type ICE1-like transcription factor, SlICE1a, confers cold, osmotic and salt tolerance in transgenic tobacco.

ICE1 (inducer of CBF expression 1), a MYC-type bHLH transcription factor, is an important activator of CBF3/DREB1A for regulating cold signaling and stress tolerance. In this study, we isolated the novel ICE1-like gene SlICE1a from tomato which contains the conserved bHLH domain, an S-rich motif, and ACT-domain. It is localized in the nucleus and harbors transcription-activating activity in the N-terminal. In addition, the SlICE1a transcript is slightly upregulated by cold stress, salt stress, and osmotic stress. SlICE1a overexpression in tobacco enhances the induction of CBF/DREB and their target genes, consequently increasing the levels of proline, soluble sugars, and late embryogenesis abundant (LEA) proteins, and enhancing tolerance to cold stress, osmotic stress, and salt stress. SlICE1a functions in abiotic stress responses by regulating the expression of stress-tolerant genes, and is thus beneficial for crop improvement.

Overexpression of thylakoidal ascorbate peroxidase shows enhanced resistance to chilling stress in tomato.

Photosynthesis provides a strong reducing power and a high risk for generation of reactive oxygen species (ROS) particularly under chilling stress. Ascorbate peroxidases (APXs) reduce H(2)O(2) to water and play an important role in the antioxidant system of plants. Though thylakoid ascorbate peroxidase (tAPX) has been thought to be key regulator of intracellular levels of H(2)O(2), its physiological significance in the response to chilling stress is still under discussion. To study the contribution of tAPX to the ROS scavenging, a tomato thylakoidal ascorbate peroxidase gene (LetAPX) was isolated and transgenic tomatoes were obtained. The LetAPX-GFP fusion protein was targeted to chloroplast in Arabidopsis mesophyll protoplast. RNA blotting analysis revealed that the LetAPX transcript expression was up-regulated by chilling, high light, exogenous salicylic acid (SA) and methyl viologen (MV). Over expression of LetAPX in tomatoes conferred tolerance to chilling stress by maintaining higher reduced glutathione (GSH) content, chlorophyll and APX activities compared with wild type (WT) plants. Furthermore, transgenic plants showed lower levels of hydrogen peroxide (H(2)O(2)) and ion leakage, lower malendialdehyde (MDA) content, higher net photosynthetic rate (Pn) and higher maximal photochemical efficiency of PSII (Fv/Fm). The oxidizable P700 decreased more obviously in WT than that in transgenic plants under chilling stress in low irradiance. The results suggested that over expression of tAPX played a key role both in alleviating photo inhibition of PSI and PSII and enhancing their tolerance to chilling stress.

Overexpression and suppression of violaxanthin de-epoxidase affects the sensitivity of photosystem II photoinhibition to high light and chilling stress in transgenic tobacco.

Tobacco (Nicotiana tabacum) transformed with the sense and antisense constructs of tomato (Lycopersicon esculentum) violaxanthin de-epoxidase gene (LeVDE) was obtained under the control of the cauliflower mosaic virus 35S promoter (35S-CaMV). Reverse transcription-polymerase chain reaction and western blot analysis demonstrated that the exogenous gene was integrated into the tobacco genome. Wild type (WT), the sense-transgenic line T(1)-24(+) and the antisense-transgenic line T(1)-17(-) were used for physiological measurement. The ratio of (A+Z)/(V+A+Z) and non-photochemical quenching in WT were lower than that in sense plants and higher than that in antisense ones under high light and chilling stress with low irradiance. The maximal photochemical efficiency of photosystem II (PSII) (Fv/Fm) and the net photosynthetic rate (Pn) in the sense line decreased less, while Fv/Fm and Pn in the antisense line decreased most obviously among all lines. These results suggest that the expression of the violaxanthin de-epoxidase gene in transgenic plants affects the sensitivity of PSII photoinhibition to high light and chilling stress.

Overexpression of violaxanthin de-epoxidase gene alleviates photoinhibition of PSII and PSI in tomato during high light and chilling stress.

A tomato (Lycopersicon esculentum) violaxanthin de-epoxidase gene (LeVDE) was isolated. The deduced amino acid sequence of LeVDE showed high identities with violaxanthin de-epoxidase in other plant species. RNA gel blot analysis showed that the mRNA accumulation of LeVDE in the wild-type (WT) was regulated by diurnal rhythm and temperature. RNA and protein gel blot analyses confirmed that the sense LeVDE was transferred into the tomato genome and overexpressed under the control of 35S-CaMV. The ratio of (A+Z)/(V+A+Z) and the values of non-photochemical quenching (NPQ) were higher in transgenic plants than those in WT under high light and chilling stress (4 degrees C). The net photosynthetic rate (Pn) decreased markedly in WT compared to transgenic lines under high light stress. The maximum quantum yield of primary photochemistry of PSII (Fv/Fm) in transgenic plants decreased more slowly during stresses and recovered faster than that in WT under optimal conditions. The oxidizable P700 in transgenic plants was higher than that in WT under chilling stress. These results suggest that overexpression of LeVDE increased the function of the xanthophyll cycle and alleviated photoinhibition of PSII and PSI in tomato during high light and chilling stress with low irradiance.