Basic helix-loop-helix (bHLH) transcription factors are widely distributed in eukaryotic organisms and are thought to be one of the largest families of regulatory proteins. This important family of transcriptional regulators plays crucial roles in plant development. However, a systematic analysis of the bHLH transcription factor family has not been reported in Chinese cabbage. In this study, 230 bHLH transcription factors were identified from the whole Chinese cabbage genome and compared with proteins from other representative plants, fungi and metazoans. The Chinese cabbage bHLH (BrabHLH) gene family could be classified into 24 subfamilies. Phylogenetic analysis of BrabHLHs along with bHLHs from Arabidopsis and rice indicated 26 subfamilies. The identification, classification, phylogenetic reconstruction, conserved motifs, chromosome distribution, functional annotation, expression patterns and interaction networks of BrabHLHs were analyzed. Distribution mapping showed that BrabHLHs were non-randomly located on the ten Chinese cabbage chromosomes. One hundred and twenty-four orthologous bHLH genes were identified between Chinese cabbage and Arabidopsis, and the interaction networks of the orthologous genes were constructed in Chinese cabbage. Quantitative RT-PCR analysis showed that expressions of BrabHLH genes varied widely under different abiotic stress treatments for different times. Thus, this comprehensive analysis of BrabHLHs represents a rich resource, aiding the elucidation of the roles of bHLH family members in plant growth and development. Furthermore, the comparative genomics analysis deepened our understanding of the evolution of this gene family after a polyploidy event.

The Hsf gene family, one of the most important transcription factor families, plays crucial roles in regulating heat resistance. However, a systematic and comprehensive analysis of this gene family has not been reported in Chinese cabbage. Therefore, systematic analysis of the Hsf gene family in Chinese cabbage has profound significance. In this study, 35 BrHsf genes were identified from Chinese cabbage, which could be classified into three groups according to their structural characteristics and phylogenetic comparisons with Arabidopsis and rice. Thirty-three BrHsf genes mapped on chromosomes were further assigned to three subgenomes and eight ancestral karyotypes. Distribution mapping showed that BrHsf genes were non-randomly localized on chromosomes. Chinese cabbage and Arabidopsis shared 22 orthologous gene pairs. The expansion of BrHsf genes mainly resulted from genome triplication. Comparative analysis showed that the most Hsf genes were in Chinese cabbage among the five species analyzed. Interestingly, the number of Hsf genes of heat-resistant plants (Theobroma cacao and Musa acuminata) was fewer than that in Chinese cabbage. The expression patterns of BrHsf genes were different in six tissues, based on RNA-seq. Quantitative real-time-PCR analysis showed that the expression level of BrHsf genes varied under various abiotic stresses. In conclusion, this comprehensive analysis of BrHsf genes will provide rich resources, aiding the determination of Hsfs functions in plant heat resistance. Furthermore, the comparative genomics analysis deepened our understanding of Hsf genes' evolution accompanied by the polyploidy event of Chinese cabbage.

The glyoxalase pathway is composed of glyoxalase I (GLYI) and glyoxalase II (GLYII) and is responsible for the detoxification of a cytotoxic metabolite methylglyoxal (MG) into the non-toxic S-D-lactoylglutathione. The two glyoxalase enzymes play a crucial role in stress tolerance in various plant species. Recently, the GLY gene families have well been analyzed in Arabidopsis, rice and soybean, however, little is known about them in Chinese cabbage (Brassica rapa). Here, 16 BrGLYI and 15 BrGLYII genes were identified in the B. rapa genome, and the BrGLYI and BrGLYII proteins were both clustered into five subfamilies. The classifications, chromosomal distributions, gene duplications, exon-intron structures, localizations, conserved motifs and promoter cis-elements were also predicted and analyzed. In addition, the expression pattern of these genes in different tissues and their response to biotic and abiotic stresses were analyzed using publicly available data and a quantitative real-time PCR analysis (RT-qPCR). The results indicated that the expression profiles of BrGLY genes varied among different tissues. Notably, a number of BrGLY genes showed responses to biotic and abiotic stress treatments, including Plasmodiophora brassi-cae infection and various heavy metal stresses. Taken together, this study identifies BrGLYI and BrGLYII gene families in B. rapa and offers insight into their roles in plant development and stress resistance, especially in heavy metal stress tolerance and pathogen resistance.

BackgroundNon-heading Chinese cabbage (NHCC, Brassica rapa ssp. chinensis) is an important leaf vegetable grown worldwide. However, little is known about the molecular mechanisms underlying tolerance for extreme temperature in NHCC. The limited availability of NHCC genomic information has greatly hindered functional analysis and molecular breeding.ResultsHere, we conduct comprehensive analyses of cold and heat treatments in NHCC using RNA-seq. Approximately 790 million paired-end reads representing 136,189 unigenes with N50 length of 1705 bp were obtained. Totally, 14,329 differentially expressed genes (DEGs) were detected. Among which, 10 DEGs were detected in all treatments, including 7 up-regulated and 3 down-regulated. The enrichment analyses showed 25 and 33 genes were enriched under cold and heat treatments, respectively. Additionally, 10,001 LncRNAs were identified, and 9,687 belonged to novel LncRNAs. The expression of miRNAs were more than that of pri-miRNAs and LncRNAs. Furthermore, we constructed a coexpression network for LncRNAs and miRNAs. It showed 67 and 192 genes were regulated by LncRNAs under cold and heat treatments, respectively. We constructed the flowchart for identifying LncRNAs of NHCC using transcriptome. Except conducting the de novo transcriptome analyses, we also compared these unigenes with the Chinese cabbage proteins. We identified several most important genes, and discussed their regulatory networks and crosstalk in cold and heat stresses.ConclusionsWe presented the first comprehensive characterization for NHCC crops and constructed the flowchart for identifying LncRNAs using transcriptome. Therefore, this study represents a fully characterized NHCC transcriptome, and provides a valuable resource for genetic and genomic studies under abiotic stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2625-2) contains supplementary material, which is available to authorized users.

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