State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources/Guangdong Provincial Key Laboratory of Postharvest Science of Fruits and Vegetables, College of Horticulture, South China Agricultural University, Guangzhou 510642, PR China.
Institute of Food Science, Zhejiang Academy of Agricultural Science/Key Laboratory of Post-Harvest Handing of Fruits, Ministry of Agriculture, Key Laboratory of Fruits and Vegetables Postharvest and Processing Technology Research of Zhejiang Province, Key Laboratory of China Light Industry, Hangzhou 310021, PR China.
Plant Cell Physiol. 2017 Dec 1;58(12):2155-2165. doi: 10.1093/pcp/pcx149.
Papaya is an important tropical fruit with a rich source of carotenoids. The ripening of papaya is a physiological and metabolic process with remarkable changes including accumulation of carotenoids, which depends primarily on the action of ethylene. Ethylene response is mediated by a transcriptional cascade involving the transcription factor families of EIN3/EILs and ERFs. Although ERF members have been reported to control carotenoid production in Arabidopsis and tomato, whether EIN3/EILs are also involved in carotenoid biosynthesis during fruit ripening remains unclear. In this work, two EIN3 genes from papaya fruit, namely CpEIN3a and CpEIN3b, were studied, of which CpEIN3a was increased during fruit ripening, concomitant with the increase of transcripts of carotenoid biosynthesis-related genes including CpPDS2/4, CpZDS, CpLCY-e and CpCHY-b, and carotenoid content. Electrophoretic mobility shift assays (EMSAs) and transient expression analyses revealed that CpEIN3a was able to bind to the promoters of CpPDS4 and CpCHY-b, and promoted their transcription. Protein-protein interaction assays indicated that CpEIN3a physically interacted with another transcription factor CpNAC2, which acted as a transcriptional activator of CpPDS2/4, CpZDS, CpLCY-e and CpCHY-b by directly binding to their promoters. More importantly, the transcriptional activation abilities of CpPDS2/4, CpLCY-e and CpCHY-b were more pronounced following their interaction. Collectively, our findings suggest that CpEIN3a interacts with CpNAC2 and, individually or co-operatively, activates the transcription of a subset of carotenoid biosynthesis-related genes, providing new insights into the regulatory networks of carotenoid biosynthesis during papaya fruit ripening.
番木瓜是一种重要的热带水果，其类胡萝卜素含量丰富。番木瓜的成熟是一个生理和代谢过程，伴随着包括类胡萝卜素积累在内的显著变化，而这主要依赖于乙烯的作用。乙烯的反应是通过一个转录级联来介导的，涉及到 EIN3/EILs 和 ERF 转录因子家族。尽管已经有报道称 ERF 成员控制拟南芥和番茄中的类胡萝卜素产生，但 EIN3/EILs 是否也参与果实成熟过程中的类胡萝卜素生物合成仍不清楚。在这项工作中，研究了来自番木瓜果实的两个 EIN3 基因，即 CpEIN3a 和 CpEIN3b，其中 CpEIN3a 在果实成熟过程中增加，伴随着类胡萝卜素生物合成相关基因包括 CpPDS2/4、CpZDS、CpLCY-e 和 CpCHY-b 的转录物的增加，以及类胡萝卜素含量的增加。电泳迁移率变动分析（EMSA）和瞬时表达分析表明，CpEIN3a 能够与 CpPDS4 和 CpCHY-b 的启动子结合，并促进它们的转录。蛋白-蛋白相互作用分析表明，CpEIN3a 与另一个转录因子 CpNAC2 相互作用，CpNAC2 通过直接结合其启动子，作为 CpPDS2/4、CpZDS、CpLCY-e 和 CpCHY-b 的转录激活因子。更重要的是，CpPDS2/4、CpLCY-e 和 CpCHY-b 的转录激活能力在它们相互作用后更为明显。总的来说，我们的研究结果表明，CpEIN3a 与 CpNAC2 相互作用，并单独或合作激活一组类胡萝卜素生物合成相关基因的转录，为番木瓜果实成熟过程中类胡萝卜素生物合成的调控网络提供了新的见解。
