Abstract
Chinese kale (Brassica oleracea var. chinensis Lei) is an important vegetable crop in South China, valued for its nutritional content and taste. Nonetheless, the thermal tolerance of Chinese kale still needs improvement. Molecular characterization of Chinese kale’s heat stress response could provide a timely solution for developing a thermally tolerant Chinese kale variety. Here, we report the cloning of multi-protein bridging factor (MBF) 1c from Chinese kale (BocMBF1c), an ortholog to the key heat stress responsive gene MBF1c. Phylogenetic analysis showed that BocMBF1c is highly similar to the stress-response transcriptional coactivator MBF1c from Arabidopsis thaliana (AtMBF1c), and the BocMBF1c coding region conserves MBF1 and helix-turn-helix (HTH) domains. Moreover, the promoter region of BocMBF1c contains three heat shock elements (HSEs) and, thus, is highly responsive to heat treatment. This was verified in Nicotiana benthamiana leaf tissue using a green fluorescent protein (GFP) reporter. In addition, the expression of BocMBF1c can be induced by various abiotic stresses in Chinese kale which indicates the involvement of stress responses. The BocMBF1c-eGFP (enhanced green fluorescent protein) chimeric protein quickly translocated into the nucleus under high temperature treatment in Nicotiana benthamiana leaf tissue. Overexpression of BocMBF1c in Arabidopsis thaliana results in a larger size and enhanced thermal tolerance compared with the wild type. Our results provide valuable insight for the role of BocMBF1c during heat stress in Chinese kale.
Highlights
Chinese kale (Brassica oleracea var. chinensis Lei Syn:Brassica alboglabra Bailey) is a popular vegetable for its health benefits and taste [1]
Open reading fragment (ORF) prediction by ORF finder did not find any intron within the BocMBF1c gene, which was confirmed by agarose gel analysis (Figure S1)
Phylogenetic analysis indicated that BocMBF1c clustered with Arabidopsis Multi-protein bridging factor1c (MBF1c) (Figure 1b, Table S1)
Summary
Chinese kale (Brassica oleracea var. chinensis Lei Syn:Brassica alboglabra Bailey) is a popular vegetable for its health benefits and taste [1]. Many plant hormones are reported in the heat response of plants, and exogenous application of plant hormones can activate expression of heat stress-related genes improving thermal tolerance. Application of ET and jasmonic acid (JA) can activate thermal stress-related genes by upregulating ethylene response factor (ERF) 1 in Arabidopsis. In addition to HSF- and HSP-responsive pathways [9], the transcriptional coactivator Multi-protein bridging factor1c (MBF1c) was identified as a critical regulator for thermal tolerance responses in Arabidopsis [10]. In Arabidopsis, heat stress can lead to increased expression of AtMBF1c and triggers the nuclear localization of AtMBF1c proteins. MBF1c is an ideal gene for improving plant thermal tolerance and, increase productivity under heat stress. We reported the ortholog of AtMBF1c in Chinese kale, termed BocMBF1c, and characterized its potential role in regulating heat tolerance in Chinese kale
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