Auxin response factors (ARFs) are involved in auxin-mediated transcriptional regulation in plants. In this study, we performed functional characterization of SlARF6A in tomato. SlARF6A is located in the nucleus and exhibits transcriptional activator activity. Overexpression of SlARF6A increased chlorophyll contents in the fruits and leaves of tomato plants, whereas downregulation of SlARF6A decreased chlorophyll contents compared with those of wild-type (WT) plants. Analysis of chloroplasts using transmission electron microscopy indicated increased sizes of chloroplasts in SlARF6A-overexpressing plants and decreased numbers of chloroplasts in SlARF6A-downregulated plants. Overexpression of SlARF6A increased the photosynthesis rate and accumulation of starch and soluble sugars, whereas knockdown of SlARF6A resulted in opposite phenotypes in tomato leaves and fruits. RNA-sequence analysis showed that regulation of SlARF6A expression altered the expression of genes involved in chlorophyll metabolism, photosynthesis and sugar metabolism. SlARF6A directly bound to the promoters of SlGLK1, CAB, and RbcS genes and positively regulated the expression of these genes. Overexpression of SlARF6A also inhibited fruit ripening and ethylene production, whereas downregulation of SlARF6A increased fruit ripening and ethylene production. SlARF6A directly bound to the SAMS1 promoter and negatively regulated SAMS1 expression. Taken together, these results expand our understanding of ARFs with regard to photosynthesis, sugar accumulation and fruit development and provide a potential target for genetic engineering to improve fruit nutrition in horticulture crops.

FGF19 promotes epithelial-mesenchymal transition in hepatocellular carcinoma cells by modulating the GSK3β/β- catenin signaling cascade via FGFR4 activation

The photosynthesis of green tomatoes contributes to fruit growth and carbon economy. The tomato auxin response factor 10 (SlARF10) belongs to the ARF family and is located in nucleus. In this study, we found that SlARF10 was highly expressed in green fruit. Overexpression of SlARF10 in fruit produced a dark-green phenotype whilst knock-down by RNAi produced a light-green phenotype. Autofluorescence and chlorophyll content analyses confirmed the phenotypes, which indicated that SlARF10 plays an important role in chlorophyll accumulation. Overexpression of SlARF10 positively affected photosynthesis in both leaves and fruit. Furthermore, SlARF10-overexpression lines displayed improved accumulation of starch, fructose, and sucrose in fruit, whilst SlARF10-RNAi lines showed decreased accumulation of starch and sucrose. Regulation of SlARF10 expression altered the expression of AGPase starch biosynthesis genes. SlARF10 positively regulated the expression of SlGLK1, POR, CBP1, and CBP2, which are related to chlorophyll metabolism and regulation. Electrophoretic mobility shift assays confirmed that SlARF10 directly targets to the SlGLK1 promoter. Our results thus indicate that SlARF10 is involved in chlorophyll accumulation by transcriptional activation of SlGLK1 expression in tomato fruit, and provide insights into the link between auxin signaling, chloroplast activity, and sugar metabolism during tomato fruit development.

The tumor microenvironment induces endoplasmic reticulum (ER) stress in tumor cells, an event that can promote progression, but it is unknown how tumor cells adapt to this stress. In this study, we show that the fibroblast growth factor FGF19, a gene frequently amplified in hepatocellular carcinoma (HCC), facilitates a survival response to ER stress. Levels of FGF19 expression were increased in stressed HCC cells in culture and in a mouse xenograft model. Induction of ER stress required the transcription factor ATF4, which directly bound the FGF19 promoter. In cells where ER stress was induced, FGF19 overexpression promoted HCC cell survival and increased resistance to apoptosis, whereas FGF19 silencing counteracted these effects. Mechanistic investigations implicated glycogen synthase kinase-3β (GSK3β) in regulating nuclear accumulation of the stress-regulated transcription factor Nrf2 activated by FGF19. Our findings show how FGF19 provides a cytoprotective role against ER stress by activating a FGFR4–GSK3β–Nrf2 signaling cascade, with implications for targeting this signaling node as a candidate therapeutic regimen for HCC management. Cancer Res; 77(22); 6215–25. ©2017 AACR.

Tomato trichomes act as a mechanical and chemical barrier against pests. An R2R3 MYB transcription factor gene, SlMYB75, is highly expressed in type II, V, and VI trichomes. SlMYB75 protein is located in the nucleus and possesses transcriptional activation activity. Down-regulation of SlMYB75 increased the formation of type II, V, and VI trichomes, accumulation of δ-elemene, β-caryophyllene, and α-humulene in glandular trichomes, and tolerance to spider mites in tomato. In contrast, overexpression of SlMYB75 inhibited trichome formation and sesquiterpene accumulation, and increased plant sensitivity to spider mites. RNA-Seq analyses of the SlMYB75 RNAi line indicated massive perturbation of the transcriptome, with a significant impact on several classes of transcription factors. Expression of the MYB genes SlMYB52 and SlTHM1 was strongly reduced in the RNAi line and increased in the SlMYB75-overexpressing line. SlMYB75 protein interacted with SlMYB52 and SlTHM1 and activated their expression. SlMYB75 directly targeted the promoter of the cyclin gene SlCycB2, increasing its activity. The auxin response factor SlARF4 directly targeted the promoter of SlMYB75 and inhibited its expression. SlMYB75 also bound to the promoters of the terpene synthase genes SlTPS12, SlTPS31, and SlTPS35, inhibiting their transcription. Our findings indicate that SlMYB75 perturbation affects several transcriptional circuits, resulting in altered trichome density and metabolic content.

Hepatocellular carcinoma (HCC) has very high prevalence and associated-mortality. However, targeted therapies that are currently used in clinical practice for HCC have certain limitations, in part because of the lack of reliable and clinically applicable biomarkers that can be used for diagnosis and prognosis assessments and for the surveillance of treatment effectiveness. Meta-analysis was used to analyze the integrated microarray data for global identification of a set of robust biomarkers for HCC. Quantitative RT-PCR (qRT-PCR) was performed to validate the expression levels of selected genes. Gene expression was inhibited by siRNA. CellTiter 96® AQueous One Solution Cell Proliferation assays were used to determine cell proliferation, and Transwell assays were used to determine cell migration and invasion potential. Meta-analysis of the expression data provided a gene expression signature from a total of 1525 patients with HCC, showing 1529 up-regulated genes and 478 down-regulated genes in cancer samples. The expression levels of genes having strong clinical significance were validated by qRT-PCR using primary HCC tissues and the paired adjacent noncancerous liver tissues. Up-regulation of VPS45, WIPI1, TTC1, IGBP1 and KLHL21 genes and down-regulation of FCGRT gene were confirmed in clinical HCC samples. KLHL21 was the most promising gene for potential use as a bioclinical marker in this analysis. Abrogating expression of it significantly inhibited cell proliferation, migration and invasion. Our study suggests that KLHL21 is a potential target for therapeutic intervention. Our findings also provide novel candidate genes on a genome-wide scale, which may have significant impact on the design and execution of effective therapy of HCC patients.