Cloning and Expression Analysis of the BocMBF1c Gene Involved in Heat Tolerance in Chinese Kale

Abstract

Chinese kale (<i>Brassica oleracea</i> var<i>. chinensis</i> 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 <i>multi-protein bridging factor</i> (<i>MBF</i>) <i>1c</i> from Chinese kale (<i>BocMBF1c</i>), an ortholog to the key heat stress responsive gene <i>MBF1c</i>. Phylogenetic analysis showed that <i>BocMBF1c</i> is highly similar to the stress-response transcriptional coactivator <i>MBF1c</i> from <i>Arabidopsis thaliana</i> (<i>AtMBF1c</i>), and the <i>BocMBF1c</i> coding region conserves MBF1 and helix-turn-helix (HTH) domains. Moreover, the promoter region of <i>BocMBF1c</i> contains three heat shock elements (HSEs) and, thus, is highly responsive to heat treatment. This was verified in <i>Nicotiana benthamiana</i> leaf tissue using a green fluorescent protein (GFP) reporter. In addition, the expression of <i>BocMBF1c</i> 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 <i>Nicotiana benthamiana</i> leaf tissue. Overexpression of <i>BocMBF1c</i> in <i>Arabidopsis thaliana</i> results in a larger size and enhanced thermal tolerance compared with the wild type. Our results provide valuable insight for the role of <i>BocMBF1c</i> during heat stress in Chinese kale.