Based on lipid and transcriptome analysis, Prof. Wen Weiwei from Key Laboratory of Horticultural Plant Biology (MOE), College of Horticulture and Forestry Sciences of HZAU cooperated with Prof. Cheng Yunjiang’s research group to use Newhall navel oranges and its bright mutants as materials to explore the exchange mechanism of cuticular wax and membrane lipid metabolism of sweet orange, and further elaborated the molecular basis of the increased mutant material jasmonic acid. The related achievements were published in the international academic journal Horticulture Research entitled “Lipidomic and transcriptomic analysis reveals re-allocation of carbon flux from cuticular wax into plastid membrane lipids in a glossy ‘Newhall’ navel orange mutant”. The study provides a new perspective on the natural variation of lipids in plants, especially fruit trees, and lays a molecular foundation for the cultivation of new citrus varieties and the improvement of storage and transportation.
Wax is a kind of epidermal lipid, which is important for the growth of citrus and the maintenance of post-harvest economic value. It is an “outer barrier” between the fruit and the environment. Phospholipids and glycolipids, the main components of the cell membrane, can hold the shape of the fruit and prevent the loss of water from the cells, and are an important “inner barrier” of the plant body. It was found that changes in wax content have an important effect on lipid metabolism, but this change has rarely been reported on membrane lipid research.
Through the multi-omics analysis of the fruit, the study first confirmed that the wax synthesis of the mutant was inhibited during development, and it was found that the decrease in wax synthesis was accompanied by a significant increase in the content of 36-carbon plastid lipids, mainly 36:6MGDG, 36:6DGDG, and 36:2PG. Based on the obvious increase in the chloroplast hydrolysate found in the mutant and the increase in the content of jasmonic acid, it was further inferred that the increased plastid lipid activated the lipid hydrolysis pathway to lead to the increase in jasmonic acid as it seeks to maintain the homeostasis of the lipid. We performed subcellular localization and transient overexpression of three phospholipase genes (CsDALL4, CsDAD1 and CsDALL2) whose expression levels were significantly up-regulated. Then it shows that they were all located in the chloroplast, which was consistent with the function of hydrolyzed plastid lipid. Among them, CsDAD1 and CsDALL2 can significantly reduce part of the plastid lipid content after overexpression, and promote the significant accumulation of jasmonic acid. The phospholipase hydrolysis process was the rate-limiting step in the synthesis of jasmonic acid, so CsDAD1 and CsDALL2 may be the key genes controlling the synthesis of jasmonic acid in sweet orange.
Wan Haoliang, a PhD student from MOE, College of Horticulture and Forestry Sciences of HZAU, and Liu Hongbo, a researcher from the State Key Laboratory of Crop Genetic Improvement, are the first authors of the paper, and Prof. Wen Weiwei and Cheng Yunjiang, the Key Laboratory of the ministry of education Horticultural Plant Biology, are co-corresponding authors. This research was financed by funding from the National Natural Science Foundation of China.