BackgroundThe accumulation of anthocyanin in horticultural crops not only improves their stress tolerances but also their nutritional values. Many key regulatory and structural genes in anthocyanin biosynthesis have been identified in model plants, but limited information is available for non-model plant species featured with colored leaves. In this study, two Pak Choi varieties with green or purple leaves were selected to analyze the anthocyanin biosynthesis through RNA-Seq.ResultsA total of 2475 unigenes were differentially expressed between these tested varieties, including 1303 down-regulated and 1172 up-regulated genes in the purple-leafed one. The reliability of the RNA-Seq was further confirmed by using real-time quantitative PCR. Kyoto Encyclopedia of Genes and Genomes enrichment analysis of the differentially expressed genes revealed ‘flavonoid biosynthesis’ was the only enriched pathway in the purple-leafed variety: In the pathway of phenylpropanoid metabolism, Bra017210, Bra039777, and Bra021637 were expressed at higher levels in the purple-leafed variety;　among the early anthocyanin biosynthetic genes, Bra037747 transcripts were only detected in the purple-leafed variety but not in the green-leafed one; among the late anthocyanin biosynthetic genes, Bra027457, Bra013652, Bra019350, Bra003021, Bra035004, and Bra038445 were all up-regulated in purple-leafed variety; and genes encoding anthocyanin-related transcription factors, such as Bra016164, and genes encoding anthocyanin transportation, such as GST F12, were also identified as up-regulated ones in the purple-leafed variety.ConclusionsThe current result provided a valuable insight into the anthocyanin accumulation in the purple-leafed variety of Pak Choi and a bioinformatic resource for further functional identification of key allelic genes determining the difference of anthocyanin content between Pak Choi varieties.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-3677-7) contains supplementary material, which is available to authorized users.

BackgroundGround-level ozone (O3) is one of the major air pollutants, which cause oxidative injury to plants. The physiological and biochemical mechanisms underlying the responses of plants to O3 stress have been well investigated. However, there are limited reports about the molecular basis of plant responses to O3. In this study, a comparative transcriptomic analysis of Pak Choi (Brassica campestris ssp. chinensis) exposed to different O3 concentrations was conducted for the first time.ResultsSeedlings of Pak Choi with five leaves were exposed to non-filtered air (NF, 31 ppb) or elevated O3 (E-O3, 252 ppb) for 2 days (8 h per day, from 9:00–17:00). Compared with plants in the NF, a total of 675 differentially expressed genes (DEGs) were identified in plants under E-O3, including 219 DEGs with decreased expressions and 456 DEGs with increased expressions. Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that O3 stress invoked multiple cellular defense pathways to mitigate the impaired cellular integrity and metabolism, including ‘glutathione metabolism’, ‘phenylpropanoid biosynthesis’, ‘sulfur metabolism’, ‘glucosinolate biosynthesis’, ‘cutin, suberine and wax biosynthesis’ and others. Transcription factors potentially involved in this cellular regulation were also found, such as AP2-ERF, WRKY, JAZ, MYB etc. Based on the RNA-Seq data and previous studies, a working model was proposed integrating O3 caused reactive oxygen burst, oxidation-reduction regulation, jasmonic acid and downstream functional genes for the regulation of cellular homeostasis after acute O3 stress.ConclusionThe present results provide a valuable insight into the molecular responses of Pak Choi to acute O3 stress and the specific DEGs revealed in this study could be used for further functional identification of key allelic genes determining the O3 sensitivity of Pak Choi.Electronic supplementary materialThe online version of this article (10.1186/s12870-017-1202-4) contains supplementary material, which is available to authorized users.

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In this study, impacts of O on four cultivars ('Rose', 'Pink', 'Blush' and 'White') of the polka dot plant with variegated leaves were investigated for the first time. Ozone fumigation [(120 ± 20 ppb) for 14 days (8 h day, from 8:30 to 16:30)] resulted in visible foliar injuries, decreased contents of pigments (chlorophyll a and b, and carotenoid), the inhibition of photosynthesis, the increase of quantum yield of non-regulated heat dissipation and fluorescence emission (Y(NO)), and the damage of cell membrane. Elevated O increased the content of anthocyanin (Ant). 'White' showed the highest, and 'Rose' the lowest amount of injured leaf area, indicating that the former was the most sensitive, and the latter the most tolerant to O stress. After O exposure, the highest Ant content was found in 'Rose', followed by 'Pink', 'Blush', and 'White'. Levels of Ant were likely responsible for the different sensitivities to O due to their roles in photoprotection.

Ozone (O) is one of the major pollutants in near-surface air. In order to protect sensitive plants from O pollution, many kinds of protectants including synthetic ones, were assessed in previous studies. Although they have certain protective effects, some of them are not environment-friendly. In the present study, leaf water extracts of aromatic plants [Plectranthus hadiensis var. tomentosus (PHT), Pelargonium hortorum (PHB), Tagetes patula (TP)] were compared for mitigating the damages caused by O (150 ppb for 3 days, 8 h day) on snap bean (Phaseolus vulgaris 'Jiangjunyoudou'). Our results showed that O fumigation impaired plasma membrane, decreased chlorophyll content, increased contents of malondialdehyde and superoxide anion, inhibited photosynthesis, and caused visible injury. Leaf water extracts of PHT, PHB or TP ameliorated the negative effects of O. Among them, extract of PHT showed the greatest potential to alleviate the O-caused injury, followed by PHB and TP.