Yao Lixiao, Yu Qibin, Huang Ming, Hung Weilun, Grosser Jude, Chen Shanchun, Wang Yu, Gmitter Frederick G
1Citrus Research Institute, Southwest University, Chongqing, China.
2Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850 USA.
Hortic Res. 2019 Feb 14;6:31. doi: 10.1038/s41438-018-0109-z. eCollection 2019.
Orange fruit from trees infected by ' Liberibacter asiaticus' (Las) often do not look fully mature and exhibit off-flavours described as bitter, harsh, and metallic rather than juicy and fruity. Although previous studies have been carried out to understand the effect of Las on the flavour of orange juice using metabolomic methods, the mechanisms leading to the off-flavour that occurs in Huanglongbing (HLB)-symptomatic fruit are not well understood. In this study, fruits were collected from symptomatic and healthy Valencia sweet orange () trees grafted on Swingle ( X ) rootstock. Isobaric tags for relative and absolute quantification (iTRAQ) and gas chromatography-mass spectrometry (GC-MS) were used to measure the proteins, sugars, organic acids, amino acids, and volatile terpenoids. The results showed that most of the differentially expressed proteins involved in glycolysis, the tricarboxylic acid (TCA) cycle and amino-acid biosynthesis were degraded, and terpenoid metabolism was significantly downregulated in the symptomatic fruit. Valencene, limonene, 3-carene, linalool, myrcene, and α-terpineol levels were significantly lower in fruit from Las-infected trees than from healthy trees. Similar phenomena were observed for sucrose and glucose. Our study indicated that off-flavour of symptomatic fruit was associated with a reduction in the levels of terpenoid products and the downregulation of proteins in glycolysis, the TCA cycle, and the terpenoid biosynthesis pathway.
受“亚洲韧皮杆菌”（Las）感染的橙子树所结的果实通常看起来未完全成熟，且带有被描述为苦涩、刺鼻和金属味的异味，而非多汁和果香浓郁。尽管此前已开展研究，运用代谢组学方法来了解Las对橙汁风味的影响，但导致黄龙病（HLB）症状果实出现异味的机制仍未被充分理解。在本研究中，从嫁接到枳柚（酸橙×甜橙）砧木上的出现症状和健康的伏令夏橙树上采集果实。使用相对和绝对定量等压标签（iTRAQ）和气相色谱 - 质谱联用仪（GC - MS）来测量蛋白质、糖类、有机酸、氨基酸和挥发性萜类化合物。结果表明，参与糖酵解、三羧酸（TCA）循环和氨基酸生物合成的大多数差异表达蛋白质被降解，且症状果实中的萜类代谢显著下调。感染Las的树所结果实中的瓦伦西亚烯、柠檬烯、3 - 蒈烯、芳樟醇、月桂烯和α - 萜品醇水平显著低于健康树所结果实。蔗糖和葡萄糖也观察到类似现象。我们的研究表明，症状果实的异味与萜类产物水平降低以及糖酵解、TCA循环和萜类生物合成途径中蛋白质的下调有关。
