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Background: In the agricultural areas of Qinghai-Tibet Plateau, temperature varies widely from day to night during the growing season, which makes the extreme temperature become one of the limiting factors of crop yield. Turnip (Brassica rapa var. rapa) is a traditional crop of Tibet grown in the Tibet Plateau, but its molecular and metabolic mechanisms of freezing tolerance are unclear., Results: Here, based on the changes in transcriptional and metabolic levels of Tibetan turnip under freezing treatment, the expression of the arginine decarboxylase gene BrrADC2.2 exhibited an accumulative pattern in accordance with putrescine content. Moreover, we demonstrated that BrrICE1.1 (Inducer of CBF Expression 1) could directly bind to the BrrADC2.2 promoter, activating BrrADC2.2 to promote the accumulation of putrescine, which was verified by RNAi and overexpression analyses for both BrrADC2.2 and BrrICE1.1 using transgenic hair root. The function of putrescine in turnip was further analyzed by exogenous application putrescine and its inhibitor DL-α-(Difluoromethyl) arginine (DFMA) under freezing tolerance. In addition, the BrrICE1.1 was found to be involved in the ICE1-CBF pathway to increase the freezing stress of turnip., Conclusions: BrrICE1.1 could bind the promoter of BrrADC2.2 or CBFs to participate in freezing tolerance of turnip by transcriptomics and targeted metabolomics analyses. This study revealed the regulatory network of the freezing tolerance process in turnip and increased our understanding of the plateau crops response to extreme environments in Tibet.

Calcium-dependent protein kinases (CDPKs) as crucial sensors of calcium concentration changes play important roles in responding to abiotic and biotic stresses. In this study, 55 BrrCDPK genes, which were phylogenetically clustered into four subfamilies, were identified. Chromosome locations indicated that the CDPK family in turnip expanded by segmental duplication and genome rearrangement. Moreover, gene expression profiles showed that different BrrCDPKs were expressed in specific tissues or stages. Transcript levels of BrrCDPKs indicated that they were involved in abiotic and biotic stresses and that paralogs exhibited functional divergence. Additionally, we identified 15 Rboh genes in turnip; the results of yeast two-hybrid analysis suggested that BrrRbohD1 interacted only with BrrCDPK10 and that BrrRbohD2 interacted with BrrCDPK4/7/9/10/17/22/23. Most of the genes play an important role in pst DC3000 defense by regulating the accumulation of H 2 O 2 and stomatal closure. Our study may provide an important foundation for future functional analysis of BrrCDPKs and reveal further biological roles.

Polygalacturonases (PGs) participate in pectin disassembly of cell wall and belong to one of the largest hydrolase families in plants. In this study, we identified 99 PG genes in Brassica rapa. Comprehensive analysis of phylogeny, gene structures, physico-chemical properties and coding sequence evolution demonstrated that plant PGs should be classified into seven divergent clades and each clade's members had specific sequence and structure characteristics, and/or were under specific selection pressures. Genomic distribution and retention rate analysis implied duplication events and biased retention contributed to PG family's expansion. Promoter divergence analysis using "shared motif method" revealed a significant correlation between regulatory and coding sequence evolution of PGs, and proved Clades A and E were of ancient origin. Quantitative real-time PCR analysis showed that expression patterns of PGs displayed group specificities in B. rapa. Particularly, nearly half of PG family members, especially those of Clades C, D and F, closely relates to reproductive development. Most duplicates showed similar expression profiles, suggesting dosage constraints accounted for preservation after duplication. Promoter-GUS assay further indicated PGs' extensive roles and possible redundancy during reproductive development. This work can provide a scientific classification of plant PGs, dissect the internal relationships between their evolution and expressions, and promote functional researches.

A total of 16 BnaGLN1 genes coding for cytosolic glutamine synthetase isoforms (EC 6.3.1.2.) were found in the Brassica napus genome. The total number of BnaGLN1 genes, their phylogenetic relationships, and genetic locations are in agreement with the evolutionary history of Brassica species. Two BnaGLN1.1, two BnaGLN1.2, six BnaGLN1.3, four BnaGLN1.4, and two BnaGLN1.5 genes were found and named according to the standardized nomenclature for the Brassica genus. Gene expression showed conserved responses to nitrogen availability and leaf senescence among the Brassiceae tribe. The BnaGLN1.1 and BnaGLN1.4 families are overexpressed during leaf senescence and in response to nitrogen limitation. The BnaGLN1.2 family is up-regulated under high nitrogen regimes. The members of the BnaGLN1.3 family are not affected by nitrogen availability and are more expressed in stems than in leaves. Expression of the two BnaGLN1.5 genes is almost undetectable in vegetative tissues. Regulations arising from plant interactions with their environment (such as nitrogen resources), final architecture, and therefore sink-source relations in planta, seem to be globally conserved between Arabidopsis and B. napus. Similarities of the coding sequence (CDS) and protein sequences, expression profiles, response to nitrogen availability, and ageing suggest that the roles of the different GLN1 families have been conserved among the Brassiceae tribe. These findings are encouraging the transfer of knowledge from the Arabidopsis model plant to the B. napus crop plant. They are of special interest when considering the role of glutamine synthetase in crop yield and grain quality in maize and wheat., (© The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Premise of the Study: The epidermis of Brassica rapa (turnip) cv. Tsuda contains light-induced anthocyanins, visible signs of activity of chalcone synthase (CHS), a key anthocyanin biosynthetic enzyme, which is encoded by the CHS gene family. To elucidate the regulation of this light-induced pigmentation, we isolated Brassica rapa CHS1-CHS6 (BrCHS1-CHS6) and characterized their cis-elements and expression patterns., Methods: Epidermises of light-exposed swollen hypocotyls (ESHS) were harvested to analyze transcription levels of BrCHS genes by real-time PCR. Different promoters for the genes were inserted into tobacco to examine pCHS-GUS activity by histochemistry. Yeast-one-hybridization was used to detect binding activity of BrCHS motifs to transcription factors., Key Results: Transcript levels of BrCHS1, -4, and -5 and anthocyanin-biosynthesis-related genes F3H, DFR, and ANS were high, while those of BrCHS2, -3, and -6 were almost undetectable in pigmented ESHS. However, in leaves, CHS5, F3H, and ANS expression was higher than in nonpigmented ESHS, but transcription of DFR was not detected. In the analysis of BrCHS1 and BrCHS3 promoter activity, GUS activity was strong in pigmented flowers of BrPCHS1-GUS-transformed tobacco plants, but nearly absent in BrPCHS3-GUS-transformed plants. Transcript levels of regulators, BrMYB75 and BrTT8, were strongly associated with the anthocyanin content and were light-induced. Coregulated cis-elements were found in promoters of BrCHS1,-4, and -5, and BrMYB75 and BrTT8 had high binding activities to the BrCHS Unit 1 motif., Conclusions: The chalcone synthase gene family encodes a redundant set of light-responsive, tissue-specific genes that are expressed at different levels and are involved in flavonoid biosynthesis in Tsuda turnip.

Salicylic acid is a messenger molecule in the activation of defense responses in plants. In this study, we isolated four cDNA clones representing salicylic acid-induced genes in Chinese cabbage (Brassica rapa subsp. pekinensis) by subtractive hybridization. Of the four clones, the BC5-2 clone encodes a putative glucosyltransferase protein. The BC5-3 clone is highly similar to an Arabidopsis gene encoding a putative metal-binding farnesylated protein. The BC6-1 clone is a chitinase gene with similarities to a rapeseed class IV chitinase. Class IV chitinases have deletions in the chitin-binding and catalytic domains and the BC6-1 chitinase has an additional deletion in the catalytic domain. The BCP8-1 clone is most homologous to an Arabidopsis gene that contains a tandem array of two thiJ-like sequences. These four cabbage genes were barely expressed in healthy leaves, but were strongly induced by salicylic acid and benzothiadiazole. Expression of the three genes represented by the BC5-2, BC5-3 and BCP8-1 clones were also induced by Pseudomonas syringae pv. tomato, a nonhost pathogen that elicits a hypersensitive response in Chinese cabbage. None of these four genes, however, was strongly induced by methyl jasmonate or by ethylene.