National Key Laboratory of Crop Biology & MOA Key Laboratory of Horticultural Crop Biology and Germplasm Innovation; College of Horticulture Science and Engineering, Shandong Agricultural University, Tai-An, Shandong, 271018, China.
College of Horticulture, Anhui Agricultural University, Hefei, Anhui, 230036, China.
New Phytol. 2019 Mar;221(4):1966-1982. doi: 10.1111/nph.15511. Epub 2018 Nov 1.
The plant hormone ethylene is critical for climacteric fruit ripening, while glucose and anthocyanins determine the fruit quality of climacteric fruits such as apple. Understanding the exact molecular mechanism for this process is important for elucidating the interconnection of ethylene and fruit quality. Overexpression of apple MdbHLH3 gene, an anthocyanin-related basic helix-loop-helix transcription factor (bHLH TF) gene, promotes ethylene production, and transgenic apple plantlets and trees exhibit ethylene-related root developmental abnormalities, premature leaf senescence, and fruit ripening. Biochemical analyses demonstrate that MdbHLH3 binds to the promoters of three genes that are involved in ethylene biosynthesis, including MdACO1, MdACS1, and MdACS5A, activating their transcriptional expression, thereby promoting ethylene biosynthesis. High glucose-inhibited U-box-type E3 ubiquitin ligase MdPUB29, the ortholog of Arabidopsis AtPUB29 in apple, influences the expression of ethylene biosynthetic genes and ethylene production by direct ubiquitination of the MdbHLH3 protein. Our findings provide new insights into the ubiquitination of MdbHLH3 by glucose-inhibited ubiquitin E3 ligase MdPUB29 in the regulation of ethylene biosynthesis as well as indicate that the regulatory module MdPUB29-MdbHLH3 connects ethylene biosynthesis with fruit quality in apple.
植物激素乙烯对跃变型果实成熟至关重要，而葡萄糖和花色苷决定了苹果等跃变型果实的品质。了解这一过程的确切分子机制对于阐明乙烯和果实品质之间的相互关系非常重要。过量表达与花色苷相关的基本螺旋-环-螺旋转录因子（bHLH TF）基因苹果 MdbHLH3，可促进乙烯的产生，转基因苹果苗和树木表现出与乙烯相关的根发育异常、过早的叶片衰老和果实成熟。生化分析表明，MdbHLH3 结合到参与乙烯生物合成的三个基因的启动子上，包括 MdACO1、MdACS1 和 MdACS5A，激活它们的转录表达，从而促进乙烯的生物合成。高葡萄糖抑制 U-box 型 E3 泛素连接酶 MdPUB29，是苹果中拟南芥 AtPUB29 的同源物，通过直接泛素化 MdbHLH3 蛋白影响乙烯生物合成基因的表达和乙烯的产生。我们的研究结果为葡萄糖抑制的泛素 E3 连接酶 MdPUB29 对乙烯生物合成的调控提供了新的见解，表明调控模块 MdPUB29-MdbHLH3 将乙烯生物合成与苹果果实品质联系起来。
