Anaerobic metabolism in Hevea brasiliensis laticifers is relevant to rubber synthesis when tapping is initiated
Anaerobic metabolism in Hevea brasiliensis laticifers is relevant to rubber synthesis when tapping is initiated
复制标题
开始割胶时，巴西橡胶树乳胶管中的无氧代谢与橡胶合成相关
DOI：
10.1016/j.indcrop.2022.114663
复制
发表时间：
2022-02-12
影响因子：
5.9
通讯作者：
Long, Xiangyu
中科院分区：
文献类型：
--
作者：
Qin, Yunxia;Wang, Jia;Long, Xiangyu
在巴西橡胶树中，天然橡胶的绿色工厂乳管是一种特殊的容器，其中橡胶的生物合成是主要的新陈代谢，新鲜橡胶占据了胶乳(乳管的细胞质)体积的35%-45%。有趣的是，乳胶可以复制，利用割胶过程中乳管糖酵解产生的三种基本成分(即三磷酸腺苷、乙酰辅酶A和NADPH)(一种简单的收集方法)。与蔗糖负荷和蔗糖裂解相关的一些关键基因，如HbSUT3/HbSUT1a、HbNIN2等已被发现，并有望开发出更多参与TCA循环的基因。除了好氧呼吸作用外，乳管中的厌氧发酵也很活跃，然而，厌氧代谢在乳管中的作用尚不清楚。鉴于厌氧呼吸通过补充三磷酸腺苷和中间代谢产物来帮助植物在逆境中生存所起的重要作用，我们假设它也以类似的方式参与橡胶的生物合成。为了评价乳管厌氧代谢的作用，对乳管中两个主要的发酵基因乳酸脱氢酶(LDH)和丙酮酸脱羧酶(PDC)进行了分析，并对它们的基因转录、蛋白表达、酶活性以及相应的代谢产物通量对割胶处理的响应进行了分析。综合分析结果表明，割胶后土壤有效三磷酸腺苷迅速下降，干胶产量增加。此外，HbLDH1和HbPDC4是乳管厌氧代谢的关键基因，割胶后它们被激活，乳酸含量降低3.4倍，乙醛含量增加4.6倍。此外，乙酸乙酯和乙酰辅酶A水平均迅速下降。这些结果表明，乳管的厌氧代谢是必不可少的，此外，乙醇和乳酸发酵之间的协同调节可能通过提供三磷酸腺苷或可能的中间物质醋酸酯参与橡胶的生物合成。据此建立了割胶后促进橡胶合成的厌氧发酵示意图。
In Hevea brasiliensis, the laticifers, a green factory of natural rubber, are specialised vessels in which rubber biosynthesis is the main metabolism, and fresh rubber occupies 35-45% volume of latex (the cytoplasm of laticifers). Intriguingly, Latex can be reproduced, drawing on three essential components (i.e., ATP, Acetyl-CoA and NADPH) from glycolysis in laticifers during tapping (a simple collection method). Some related key genes of sucrose loading and cleavage have been identified, such as HbSUT3/HbSUT1a, HbNIN2, and surely more genes in TCA cycle will be exploited. Besides the aerobic respiration, the anaerobic fermentation is found highly active in laticifers, however, the role of anaerobic metabolism in laticifers remains unclear. In view of the essential role of anaerobic respiration in helping plant survive adverse conditions by supplementing ATP and intermediate metabolites, we hypothesised that it would be involved in rubber biosynthesis in similar way. To assess the role of anaerobic metabolism in laticifers, two main fermentation genes, lactate dehydrogenase (LDH) and pyruvate decarboxylase (PDC) were analysed and characterised on their gene transcription, protein expression, enzyme activities, and the corresponding metabolites flux in response to tapping treatments. Our comprehensive results revealed that the available ATP decreased rapidly with tapping, accompanying by the increasement of dry rubber yield. Moreover, HbLDH1 and HbPDC4 were identified as the key genes in anaerobic metabolism of laticifers, and they were activated by tapping,indicated by a 3.4 - fold decrease in lactate content and a 4.6 - fold increase of acetaldehyde. In addition, the levels of both acetate and acetyl-CoA decreased rapidly. These results suggested that anaerobic metabolism is indispensable to laticifers, and furthermore the synergistic regulation between ethanol and lactate fermentation has been predicted to be involved in rubber biosynthesis by providing ATP or possible intermediate material acetate. A schematic diagram of anaerobic fermentation that contributes to rubber synthesis after tapping was hereby established.