A bZIP transcription factor (CiFD) regulates drought- and low-temperature-induced flowering by alternative splicing in citrus

Drought and low temperature are two key environmental factors that induce adult citrus flowering. However, the underlying regulation mechanism is poorly understood. The bZIP transcription factor FD is a key component of the florigen activation complex (FAC) which is composed of FLOWERING LOCUS T (FT), FD, and 14-3-3 proteins. In this study, isolation and characterization of CiFD in citrus found that there was alternative splicing (AS) of CiFD, forming two different proteins (CiFDα and CiFDβ). Further investigation found that their expression patterns were similar in different tissues of citrus, but the subcellular localization and transcriptional activity were different. Overexpression of the CiFD DNA sequence (CiFD-DNA), CiFDα, or CiFDβ in tobacco and citrus showed early flowering, and CiFD-DNA transgenic plants were the earliest, followed by CiFDβ and CiFDα. Interestingly, CiFDα and CiFDβ were induced by low temperature and drought, respectively. Further analysis showed that CiFDα can form a FAC complex with CiFT, Ci14-3-3, and then bind to the citrus APETALA1 (CiAP1) promoter and promote its expression. However, CiFDβ can directly bind to the CiAP1 promoter independently of CiFT and Ci14-3-3. These results showed that CiFDβ can form a more direct and simplified pathway that is independent of the FAC complex to regulate drought-induced flowering through AS. In addition, a bHLH transcription factor (CibHLH96) binds to CiFD promoter and promotes the expression of CiFD under drought condition. Transgenic analysis found that CibHLH96 can promote flowering in transgenic tobacco. These results suggest that CiFD is involved in drought- and low-temperature-induced citrus flowering through different regulatory patterns.

Citrus FRIGIDA cooperates with its interaction partner dehydrin to regulate drought tolerance

Drought is a major environmental stress that severely affects plant growth and crop productivity. FRIGIDA (FRI) is a key regulator of flowering time and drought tolerance in model plants. However, little is known regarding its functions in woody plants, including citrus. Thus, we explored the functional role of the citrus FRI ortholog (CiFRI) under drought. Drought treatment induced CiFRI expression. CiFRI overexpression enhanced drought tolerance in transgenic Arabidopsis and citrus, while CiFRI suppression increased drought susceptibility in citrus. Moreover, transcriptomic profiling under drought conditions suggested that CiFRI overexpression altered the expression of numerous genes involved in the stress response, hormone biosynthesis, and signal transduction. Mechanistic studies revealed that citrus dehydrin likely protects CiFRI from stress-induced degradation, thereby enhancing plant drought tolerance. In addition, a citrus brassinazole-resistant (BZR) transcription factor family member (CiBZR1) directly binds to the CiFRI promoter to activate its expression under drought conditions. CiBZR1 also enhanced drought tolerance in transgenic Arabidopsis and citrus. These findings further our understanding of the molecular mechanisms underlying the CiFRI-mediated drought stress response in citrus.

A MADS-Box Gene CiMADS43 Is Involved in Citrus Flowering and Leaf Development through Interaction with CiAGL9

MADS-box genes are involved in various developmental processes including vegetative development, flower architecture, flowering, pollen formation, seed and fruit development. However, the function of most MADS-box genes and their regulation mechanism are still unclear in woody plants compared with model plants. In this study, a MADS-box gene (CiMADS43) was identified in citrus. Phylogenetic and sequence analysis showed that CiMADS43 is a GOA-like Bsister MADS-box gene. It was localized in the nucleus and as a transcriptional activator. Overexpression of CiMADS43 promoted early flowering and leaves curling in transgenic Arabidopsis. Besides, overexpression or knockout of CiMADS43 also showed leaf curl phenotype in citrus similar to that of CiMADS43 overexpressed in Arabidopsis. Protein–protein interaction found that a SEPALLATA (SEP)-like protein (CiAGL9) interacted with CiMADS43 protein. Interestingly, CiAGL9 also can bind to the CiMADS43 promoter and promote its transcription. Expression analysis also showed that these two genes were closely related to seasonal flowering and the development of the leaf in citrus. Our findings revealed the multifunctional roles of CiMADS43 in the vegetative and reproductive development of citrus. These results will facilitate our understanding of the evolution and molecular mechanisms of MADS-box genes in citrus.

[Bioinformatics analysis of key genes and prognosis-related genes during the onset of hepatocellular carcinoma]

Objective: To screen and analyze the differentially-expressed genes (DEGs) in primary hepatocellular carcinoma tissues and adjacent tissues using bioinformatics methods to explore the molecular mechanism of the occurrence and prognosis of primary hepatocellular carcinoma. Methods: GSE76427 data set was collected through GEO database, and DEGs were identified using GEO2R online analysis. Go and KEGG databases were used for enrichment and functional annotation of DEGs. Protein interaction network was built based on the STRING database and Cytoscape software to analyze the key genes of hepatocellular carcinoma, and the survival curve of these key genes were analyzed using the GEPIA database. Results: A total of 74 hepatocellular carcinoma DEGs were screened, of which 3 and 71 were up-and-down-regulated genes. The results of GO enrichment analysis showed that the down-regulated DEGs were mainly involved in cell response to cadmium and zinc ions, negative growth regulation, heterologous metabolic processes and hormone-mediated signaling pathways. KEGG pathway enrichment analysis results showed that the down-regulated DEGs pathway were mainly involved in retinol metabolism, chemical carcinogenesis, drug metabolism-cytochrome P450, cytochrome P450 metabolizing xenobiotics, tryptophan metabolism and caffeine metabolism. Protein interaction network had screened out 10 down-regulated core genes: MT1G, MT1F, MT1X, MT1E, MT1H, insulin-like growth factor 1, FOS, CXCL12, EGR1, and BGN. Among them, the insulin-like growth factor 1 was related to the prognosis of primary hepatocellular carcinoma. Conclusion: Bioinformatics analysis results of HCC chip data showed that 10 key genes may play a key role in the occurrence and development of HCC and the insulin like growth factor 1 is associated with the prognosis of primary hepatocellular carcinoma.

[Integrated analysis of DNA methylation and gene expression profiles of hepatocellular carcinoma to construct miR-1180-3p relevant ceRNA regulatory network]

Objective: This study analyzes the expression level of miR-1180-3p and constructs the regulatory network of relevant ceRNA by integrating the DNA methylation and gene expression profile of hepatocellular carcinoma from the Cancer Genome Atlas (TCGA). Methods: Firstly, the expression level of miR-1180-3p in hepatocellular carcinoma and adjacent tissues was analyzed by TCGA database, and the differential expression of lncrna and mRNA was screened. Secondly, the LncBase database and the TargetScan database were used to predict the relationship between miR-1180-3p and lncRNA and mRNA, and the DNA methylation-mediated lncRNA was screened by the DNA methylation profile of lncRNA. Finally, Cytoscape software was used to construct miR-1180-3p relevant ceRNA network, and WebGestalt website was used to perform GO and KEGG analysis of related mRNA in ceRNA. Results: Compared with patients with low expression of miR-1180-3p (mean overall survival duration, 5.69 ± 0.35 years), patients with high expression of miR-1180-3p had shorter overall survival time (mean overall survival duration, 3.99 ± 0.47 years), indicating that the high expression of miR-1180-3p was hepatocellular carcinoma risk factor affecting the prognosis (HR = 1.28, 95% CI = 1.1 ~ 1.5, P < 0.01). A miR-1180-3p related ceRNA regulatory network was constructed in this study, which contained 2 lncRNAs (F11-AS1 and LINC01511) and 37 mRNAs. Conclusion: This study has successfully constructed miR-1180-3p relevant ceRNA regulatory network, and DNA methylation-mediated F11-AS1 and F11-AS1/miR-1180-3p/C11of54 ceRNA regulatory axis has played an important role in the occurrence and development of hepatocellular carcinoma.