Identification of DELLA Genes and Key Stage for GA Sensitivity in Bolting and Flowering of Flowering Chinese Cabbage

Flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) is an important and extensively cultivated vegetable in south China, and its stalk development is mainly regulated by gibberellin (GA). DELLA proteins negatively regulate GA signal transduction and may play an important role in determining bolting and flowering. Nevertheless, no systematic study of the DELLA gene family has been undertaken in flowering Chinese cabbage. In the present study, we found that the two-true-leaf spraying of gibberellin A3 (GA3) did not promote bolting but did promote flowering, whereas the three-true-leaf spraying of GA3 promoted both bolting and flowering. In addition, we identified five DELLA genes in flowering Chinese cabbage. All five proteins contained DELLA, VHYNP, VHIID, and SAW conserved domains. Protein-protein interaction results showed that in the presence of GA3, all five DELLA proteins interacted with BcGID1b (GA-INSENSITIVE DWARF 1b) but not with BcGID1a (GA-INSENSITIVE DWARF 1a) or BcGID1c (GA-INSENSITIVE DWARF 1c). Their expression analysis showed that the DELLA genes exhibited tissue-specific expression, and their reversible expression profiles responded to exogenous GA3 depending on the treatment stage. We also found that the DELLA genes showed distinct expression patterns in the two varieties of flowering Chinese cabbage. BcRGL1 may play a major role in the early bud differentiation process of different varieties, affecting bolting and flowering. Taken together, these results provide a theoretical basis for further dissecting the DELLA regulatory mechanism in the bolting and flowering of flowering Chinese cabbage.

Transcriptional Controls for Early Bolting and Flowering in Angelica sinensis

The root of the perennial herb Angelica sinensis is a widely used source for traditional Chinese medicines. While the plant thrives in cool-moist regions of western China, early bolting and flowering (EBF) for young plants significantly reduces root quality and yield. Approaches to inhibit EBF by changes in physiology during the vernalization process have been investigated; however, the mechanism for activating EBF is still limited. Here, transcript profiles for bolted and unbolted plants (BP and UBP, respectively) were compared by transcriptomic analysis, expression levels of candidate genes were validated by qRT-PCR, and the accumulations of gibberellins (GA1, GA4, GA8, GA9 and GA20) were also monitored by HPLC-MS/MS. A total of over 72,000 unigenes were detected with ca. 2600 differentially expressed genes (DEGs) observed in the BP compared with UBP. While various signaling pathways participate in flower induction, it is genes associated with floral development and the sucrose pathway that are observed to be coordinated in EBF plants, coherently up- and down-regulating flowering genes that activate and inhibit flowering, respectively. The signature transcripts pattern for the developmental pathways that drive flowering provides insight into the molecular signals that activate plant EBF.

Poplar aquaporin PIP1;1 promotes Arabidopsis growth and development

Background Root hydraulic conductance is primarily determined by the conductance of living tissues to radial water flow. Plasma membrane intrinsic proteins (PIPs) in root cortical cells are important for plants to take up water and are believed to be directly involved in cell growth. Results In this study, we found that constitutive overexpression of the poplar root-specific gene PtoPIP1;1 in Arabidopsis accelerated bolting and flowering. At the early stage of the developmental process, PtoPIP1;1 OE Arabidopsis exhibited faster cell growth in both leaves and roots. The turgor pressure of plants was correspondingly increased in PtoPIP1;1 OE Arabidopsis, and the water status was changed. At the same time, the expression levels of flowering-related genes (CRY1, CRY2 and FCA) and hub genes in the regulatory networks underlying floral timing (FT and SOC1) were significantly upregulated in OE plants, while the floral repressor FLC gene was significantly downregulated. Conclusions Taken together, the results of our study indicate that constitutive overexpression of PtoPIP1;1 in Arabidopsis accelerates bolting and flowering through faster cell growth in both the leaf and root at an early stage of the developmental process. The autonomous pathway of flowering regulation may be executed by monitoring developmental age. The increase in turgor and changes in water status with PtoPIP1;1 overexpression play a role in promoting cell growth.

Effect of Nitrate Concentration on the Growth, Bolting and Related Gene Expression in Flowering Chinese Cabbage

Nitrogen concentration affects growth and bolting of plants, but its regulation mechanism is still unclear. In this work, three nitrate concentration treatments (5%, 100%, 200%) in nutrient solution were conducted to explore the internal relationship between nitrogen and bolting in flowering Chinese cabbage. The results showed that the bolting and flowering time was earlier under the treatment with low nitrate and, the lower the nitrate concentration, the earlier the bolting and flowering. Low-nitrate treatment reduced the content of nitrate, soluble protein, free amino acid and total nitrogen, and increased the C/N ratio. The C/N ratio was significantly negatively correlated with plant height, stem thickness and biomass, while it was significantly positively correlated with flowering rate. Thus, it was indicated that nitrogen may affect bolting and flowering by regulating the C/N ratio of flowering Chinese cabbage plants. The expression of flowering-related genes (SOC1, LFY) was increased significantly under low nitrate treatment. In addition, the pith cell area at the stem tip was significantly reduced under low nitrate treatment, resulting in a significant decrease in stem thickness. The expression of cyclin- and expansin-related genes (CYCD3-3, CYCB1-1 and EXPA8) was significantly reduced, which indicated that nitrogen may regulate the stem development of flowering Chinese cabbage by regulating the expression of cyclin- and expansin-related genes.

Mapping and Identification of Genetic Loci Affecting Earliness of Bolting and Flowering in Lettuce

Bolting, defined as stem elongation, marks the plant life cycle transition from vegetative to reproductive stage. Lettuce is grown for its leaf rosettes, and premature bolting may reduce crop quality resulting in economic losses. The transition to reproductive stage is a complex process that involves many genetic and environmental factors. In this study the effects of photoperiod and ambient temperature on bolting and flowering regulation was studied by utilizing a lettuce mapping population to identify quantitative trait loci (QTL) and by gene expression analyses of genotypes with contrasting phenotypes. A recombinant inbred line (RIL) population, derived from a cross between PI251246 (early bolting) and cv. Salinas (late bolting), was grown in four combinations of short (8 hours) and long (16 hours) days and low (20°C) and high (35°C) temperature. QTL models revealed both genetic (G) and environmental (E) effects, and GxE interactions. A major QTL for bolting and flowering time was found on chromosome 7 (qFLT7.2) and two candidate genes were identified by fine mapping, homology and gene expression studies. In short days and high temperature conditions qFLT7.2 had no effect on plant development, while several small-effect loci on chromosomes 2, 3, 6, 8 and 9 were associated with bolting and flowering. Of these, the QTL on chromosome 2, qBFr2.1, co-located with the Flowering Locus T (LsFT) gene. Polymorphisms between parent genotypes in the promotor region may explain identified gene expression differences, and were used to design a genetic marker which may be used to identify the late bolting trait.

Gene co-expression network analysis reveals key pathways and hub genes in Chinese cabbage (Brassica rapa L.) during vernalization

Background Vernalization is a type of low temperature stress used to promote rapid bolting and flowering in plants. Although rapid bolting and flowering promote the reproduction of Chinese cabbages (Brassica rapa L. ssp. pekinensis), this process causes their commercial value to decline. Clarifying the mechanisms of vernalization is essential for its further application. We performed RNA sequencing of gradient-vernalization in order to explore the reasons for the different bolting process of two Chinese cabbage accessions during vernalization. Results There was considerable variation in gene expression between different-bolting Chinese cabbage accessions during vernalization. Comparative transcriptome analysis and weighted gene co-expression network analysis (WGCNA) were performed for different-bolting Chinese cabbage during different vernalization periods. The biological function analysis and hub gene annotation of highly relevant modules revealed that shoot system morphogenesis and polysaccharide and sugar metabolism caused early-bolting ‘XBJ’ to bolt and flower faster; chitin, ABA and ethylene-activated signaling pathways were enriched in late-bolting ‘JWW’; and leaf senescence and carbohydrate metabolism enrichment were found in the two Chinese cabbage-related modules, indicating that these pathways may be related to bolting and flowering. The high connectivity of hub genes regulated vernalization, including MTHFR2, CPRD49, AAP8, endoglucanase 10, BXLs, GATLs, and WRKYs. Additionally, five genes related to flower development, BBX32 (binds to the FT promoter), SUS1 (increases FT expression), TSF (the closest homologue of FT), PAO and NAC029 (plays a role in leaf senescence), were expressed in the two Chinese cabbage accessions. Conclusion The present work provides a comprehensive overview of vernalization-related gene networks in two different-bolting Chinese cabbages during vernalization. In addition, the candidate pathways and hub genes related to vernalization identified here will serve as a reference for breeders in the regulation of Chinese cabbage production.

Transcriptomic and Targeted Metabolomic Analysis Identifies Genes Controlling for Early Bolting and Flowering in Angelica Sinensis

Background: The root of the perennial herb Angelica sinensis is a widely used source for traditional Chinese medicines. While the plant thrives in cool-moist regions of western China, early bolting and flowering (EBF) for young plants, significantly reduces root quality and yield. Approaches to inhibit EBF by changes in physiology during the vernalization process have been investigated, however the mechanism for activating EBF has not been identified. Here, transcript profiles for bolted and unbolted plants (BP and UBP, respectively) are compared.Results: A total of over 72,000 unigenes were detected with ca. 2,600 differentially expressed genes (DEGs) observed in the BP compared with UBP. While various signaling pathways participate in flower induction, it is genes associated with floral development and the sucrose pathway that are observed to be coordinated in EBF plants, to coherently up and down regulate flowering genes that activate and inhibit flowering, respectively. Down-stream signal accumulation including gibberellic acids and sucrose metabolites were also monitored by HPLC-MS/MS for EBF plants.Conclusions: The signature transcripts pattern for the developmental pathways that drive flowering provides insight into the molecular signals that activate plant EBF.

Leaf Characteristics at Recovery Stage Affect Seed Oil and Protein Content Under the Interactive Effects of Nitrogen and Waterlogging in Rapeseed

Four nitrogen rates (0, 90, 180, and 270 kg ha−1) were applied to the waterlogging-tolerant variety ZS 9 and the sensitive variety GH01. Seedlings with five leaves were waterlogged for 0 (control) or 10 days to investigate the effects of nitrogen on the quality of waterlogged rapeseed. Compared with controls, the seed oil content of waterlogged rapeseed increased slightly in GH01 and significantly in ZS 9 with nitrogen application, which can be explained by the following. (1) after waterlogging, the biomass distribution in roots and leaves of ZS 9 decreased, which alleviated physiological water shortage. Conversely, biomass distribution in roots of GH01 increased, which was not synchronized with the leaf biomass change. (2) After waterlogging at 90–270 kg N ha−1, the leaf number at bolting and flowering was increased in ZS 9 but decreased in GH01 compared with the control. The decrease in leaf area and SPAD value were greater for GH01 after waterlogging, which limited photosynthesis. (3) The leaf soluble protein at bolting was highest in ZS 9 and lowest in GH01. The sensitive variety showed poor growth. The inhibition of seed protein synthesis resulted in an increase in the oil content of waterlogged rapeseed with nitrogen. The seed oil of the waterlogging-tolerant variety was most significantly negatively correlated with leaf soluble protein content at the flowering stage, while the protein content showed the opposite correlation. The seed oil of the waterlogging-sensitive variety was most significantly negatively correlated with the number of leaves at the bolting and flowering stage, while the seed protein content had opposite correlations.