Bolting In Chinese Cabbage Research Articles

A single amino acid residue substitution in BraA04g017190.3C, a histone methyltransferase, results in premature bolting in Chinese cabbage (Brassica rapa L. ssp. Pekinensis)

BackgroundFlowering is an important inflection point in the transformation from vegetative to reproductive growth, and premature bolting severely decreases crop yield and quality.ResultsIn this study, a stable early-bolting mutant, ebm3, was identified in an ethyl methanesulfonate (EMS)-mutagenized population of a Chinese cabbage doubled haploid (DH) line ‘FT’. Compared with ‘FT’, ebm3 showed early bolting under natural cultivation in autumn, and curled leaves. Genetic analysis showed that the early-bolting phenotype was controlled by a single recessive nuclear gene. Modified MutMap sequencing, genotyping analyses and allelism test provide strong evidence that BrEBM3 (BraA04g017190.3 C), encoding the histone methyltransferase CURLY LEAF (CLF), was the strongly candidate gene of the emb3. A C to T base substitution in the 14th exon of BrEBM3 resulted in an amino acid change (S to F) and the early-bolting phenotype of emb3. The mutation occurred in the SET domain (Suppressor of protein-effect variegation 3–9, Enhancer-of-zeste, Trithorax), which catalyzes site- and state-specific lysine methylation in histones. Tissue-specific expression analysis showed that BrEBM3 was highly expressed in the flower and bud. Promoter activity assay confirmed that BrEBM3 promoter was active in inflorescences. Subcellular localization analysis revealed that BrEBM3 localized in the nucleus. Transcriptomic studies supported that BrEBM3 mutation might repress H3K27me3 deposition and activate expression of the AGAMOUS (AG) and AGAMOUS-like (AGL) loci, resulting in early flowering.ConclusionsOur study revealed that an EMS-induced early-bolting mutant ebm3 in Chinese cabbage was caused by a nonsynonymous mutation in BraA04g017190.3 C, encoding the histone methyltransferase CLF. These results improve our knowledge of the genetic and genomic resources of bolting and flowering, and may be beneficial to the genetic improvement of Chinese cabbage.

A histone H4 gene prevents drought-induced bolting in Chinese cabbage by attenuating the expression of flowering genes.

Flowering is an important trait in Chinese cabbage, because premature flowering reduces yield and quality of the harvested products. Water deficit, caused by drought or other environmental conditions, induces early flowering. Drought resistance involves global reprogramming of transcription, hormone signaling, and chromatin modification. We show that a histone H4 protein, BrHIS4.A04, physically interacts with a homeodomain protein BrVIN3.1, which was selected during the domestication of late-bolting Chinese cabbage. Over-expression of BrHIS4.A04 resulted in premature flowering under normal growth conditions, but prevented further premature bolting in response to drought. We show that the expression of key abscisic acid (ABA) signaling genes, and also photoperiodic flowering genes was attenuated in BrHIS4.A04-overexpressing (BrHIS4.A04OE) plants under drought conditions. Furthermore, the relative change in H4-acetylation at these gene loci was reduced in BrHIS4.A04OE plants. We suggest that BrHIS4.A04 prevents premature bolting by attenuating the expression of photoperiodic flowering genes under drought conditions, through the ABA signaling pathway. Since BrHIS4.A04OE plants displayed no phenotype related to vegetative or reproductive development under laboratory-induced drought conditions, our findings contribute to the potential fine-tuning of flowering time in crops through genetic engineering without any growth penalty, although more data are necessary under field drought conditions.

Role of BrSDG8 on bolting in Chinese cabbage (Brassica rapa).

Mapping and resequencing of two allelic early bolting mutants ebm5-1 and ebm5-2 revealed that the BrSDG8 gene is related to bolting in Chinese cabbage (Brassica rapa ssp. pekinensis). Bolting influences the leafy head formation and seed yield of Chinese cabbage therefore being an important agronomic trait. Herein, two allelic early bolting mutants, ebm5-1 and ebm5-2, stably inherited in Chinese cabbage were obtained from wild-type 'FT' seeds by ethyl methane sulfonate mutagenesis. Both mutants flowered significantly earlier than 'FT,' and genetic analysis revealed that the early bolting of the two mutants was controlled by one recessive nuclear gene. With BSR-seq, the mutations originating lines ebm5-1 and ebm5-2 were located to the same region in chromosome A07. Using the 1741 F2 individuals with the ebm5-1 phenotype as the mapping population, this region was narrowed to 56.24kb between markers InDel18 and InDel45. A single-nucleotide polymorphism (SNP) was aligned to the BraA07g040740.3C (BrSDG8) region by whole-genome resequencing of ebm5-1 mutant and 'FT.' BrSDG8 is a homolog of Arabidopsis thaliana SDG8 encoding a histone methyltransferase affecting H3K4 trimethylation in FLOWERING LOCUS C chromatin. Comparative sequencing established that the SNP occurred on BrSDG8 17th exon in ebm5-1. Genotype analysis showed full co-segregation of the early bolting phenotype with this SNP. Cloning of allelic mutant ebm5-2 indicated that it harbors a deletion mutation on the 12th exon of BrSDG8. Quantitative real-time PCR analysis indicated that BrSDG8 expression level was observably lower in mutant ebm5-1 than in 'FT.' Overall, the present results provide strong evidence that BrSDG8 mutation leads to early bolting in Chinese cabbage, thereby providing a basis to understand the molecular mechanisms underlying this phenotype.

Regulation of bolting and identification of the α-tubulin gene family in Brassica rapa L. ssp pekinensis.

Microtubules are important components of eukaryotic cells, and they play vital roles in cell morphogenesis, carrying of signaling molecules, transport of materials, and establishing the cell polarity. During bolting of biennial plants, cell division and elongation are involved, and cell elongation inevitably involves the microtubules arrangement and expression of related genes. So we deduce that it is of great significance to figure out the mechanism of bolting and flowering in which TUA genes are involved. In the present study, bioinformatic methods were used to predict and identify the α-tubulin gene family (BrTUAs) in Brassica rapa L. ssp pekinensis (Chinese cabbage) through the alignment of AtTUA gene sequence from Arabidopsis thaliana with the B. rapa genome database (http://brassicadb.org/brad/) using the basic local alignment search tool. The change in the structure and functions of BrTUAs during the process of evolution, cis-acting elements in the promoter sequences of BrTUAs, and the expression of the identified genes was also analyzed. Twelve members of the α-tubulin gene family were identified from Chinese cabbage. The gene length, intron, exon, and promoter regions were determined to have changed significantly during the genome evolution. Only five of the 12 members were encoded completely and were observed to differ in their spatial and temporal expression. The five BrTUA promoter sequences contained different numbers of cis-elements responsive to light and low-temperature response, cis-elements responsive among which hormonal responses were significantly different. We also report that the BrTUAs were involved in the regulation of the bolting in Chinese cabbage, and propose that this process could be controlled by regulating the expression of BrTUAs.

Correlation between Bolting and Physiological Properties in Chinese Cabbage (Brassica rapa L. pekinensis Group)

To obtain physiological data on bolting in Chinese cabbage (Brassica rapa L. pekinensis Group), we conducted seed vernalization treatment using six cultivars of Chinese cabbage with different maturity times, and an experiment on spring cultivation using eight strains with different bolting properties. Soluble sugar content and peroxidase (POD) activity in seedlings in the vernalization plot that were in the flower bud differentiation stage were high in early-maturing cultivars followed by mid-season cultivars; nitrate reductase (NR) and catalase (CAT) activities were high in early-maturing cultivars compared to the control, which did not encounter low temperatures. A correlation was recognized between bolting (number of days from sowing to bud emersion) and the values of soluble sugar content and POD, NR, and CAT activities in strains with different bolting properties during the differentiation stage 15 days before bud emersion. These results show that soluble sugar content and POD, NR, and CAT activities in the flower bud differentiation stage in Chinese cabbage participate in flower bud differentiation, and it is considered that these properties are physiological indicators of bolting.

The influence of soil temperature on vernalization of Chinese cabbage

SummaryThe influence of soil-heating (30°C) on bolting of Chinese cabbage (Brassica pekinensis (Lour.) Rupr. cv. Spring A1) was studied under inductive air temperatures in growth rooms. In two experiments it was shown that warm roots had no influence on the vernalization effect but that soil heating can decrease the effect of vernalization by heat transfer into the growing point. The heat transfer is favoured by insulating the soil surface and by a short hypocotyl.

Effect of photoperiod and temperature on bolting in Chinese cabbage

One-week-old seedlings of heat-sensitive (‘Nagaoka 50’) and heat-tolerant (‘WR 85’ and ‘Saladeer’) cultivars of Chinese cabbage (Brassica pekinensis) were subjected to various temperatures (12–21°C) and photoperiods (short days (SD) of 10 h, or natural long days (ND) of 15–17 h) during a propagation period of 3 weeks before transplanting.The growth (dry weight) of the seedlings increased about 100 and 50% for ‘Nagaoka 50’ and ‘WR 85’, respectively, when the temperature was increased from 12 to 21°C in ND. In SD, the growth was less and an increase in the propagation temperature had little influence.Premature bolting and flowering were delayed for plants propagated in SD. In ‘Nagaoka 50’, the critical temperature for premature bolting and flowering in SD was below 12 and 15°C, respectively, but in ND it was above 15°C. The heat-tolerant cultivars showed similar temperature and daylength responses, but the critical temperature was considerably higher than in the case of the heat-sensitive ‘Nagaoka 50’. When the time from sowing to flowering was delayed more than 80 days, heads of satisfactory quality could be harvested.

Effect of day and night temperature at different stages of growth on bolting in Chinese cabbage

The effect of different temperature conditions in the raising period and after the transplanting stage on bolting in Chinese cabbage has been investigated. It was found that the daily mean temperature in the raising period should, in the case of heat-sensitive cultivars, be above 18°C in order to avoid premature bolting. Energy consumption during the raising period may be reduced by using high day temperatures in combination with low night temperatures. Covering the plants with plastic after transplanting in the field reduced the risk of premature bolting. With the heat-sensitive ‘Nagaoka 50’, a raising period of 4 weeks at 18°C was sufficient to prevent premature bolting under normal field conditions in April–May. The optimal raising temperature is above 24°C for the heat-tolerant ‘Saladeer’. The development of the flower stalk after the transplanting stage is dependent on factors such as daily mean temperature, stage of growth and cultivar.

Effect of plant age and temperature on bolting in Chinese cabbage

The effect of different growing methods on bolting of early Chinese cabbage was studied. Both plant age and the duration of low-temperature treatment had a significant effect on bolting. When the appearance of the flower buds was delayed as much as 80 days from sowing, the heads were of good quality. Increased plant age (1–3 weeks) at the start of cold treatment delayed bolting. Premature bolting was reduced by prolonging the raising period at a temperature above 18°C. Increasing the duration of cooling at 12°C from 1 to 3 weeks hastened bolting in the heat-sensitive ‘Nagaoka 50’. A large difference in bolting responses was found between heat-sensitive (‘Nagaoka 50’) and heat-tolerant (‘Saladeer’ and ‘Nagaoka Tropicana’) cultivars.

Flower formation of Chinese cabbage. II. Anti-vernalization and short-day treatment

The influence of high temperature (anti-vernalization) and short-day treatment during the raising of transplants on the bolting of Chinese cabbage having early planting-dates has been tested. A temperature rise from 18 to 26°C resulted in a delay in bolting, but only caused a slight increase in leaf number. Hence, Chinese cabbage shows anti-vernalization effects. The raising of transplants below 20°C and with short-day treatment for energy saving cannot be recommended, since the effect of the short-day treatment is too small.