Xiao Xiang, Lang Duoyong, Yong Jingjiao, Zhang Xinhui
College of Pharmacy, Ningxia Medical University, Yinchuan 750004, China.
College of Basic Medicine, Ningxia Medical University, Yinchuan 750004, China.
Ecotoxicol Environ Saf. 2024 Mar 15;273:116129. doi: 10.1016/j.ecoenv.2024.116129. Epub 2024 Mar 1.
The salinity environment is one of the biggest threats to Glycyrrhiza uralensis Fisch. (G. uralensis) growth, resulting from the oxidative stress caused by excess reactive oxygen species (ROS). Flavonoids are the main pharmacodynamic composition and help maintain ROS homeostasis and mitigate oxidative damage in G. uralensis in the salinity environment. To investigate whether endophytic Bacillus cereus G2 can improve the salt-tolerance of G. uralensis through controlling flavonoid biosynthesis, the transcriptomic and physiological analysis of G. uralensis treated by G2 in the saline environment was conducted, focused on flavonoid biosynthesis-related pathways. Results uncovered that salinity inhibited flavonoids synthesis by decreasing the activities of phenylalanine ammonialyase (PAL) and 4-coumarate-CoA ligase (4CL) (42% and 39%, respectively) due to down-regulated gene Glyur000910s00020578 at substrate level, and then decreasing the activities of chalcone isomerase (CHI) and chalcone synthase (CHS) activities (50% and 42%, respectively) due to down-regulated genes Glyur006062s00044203 and Glyur000051s00003431, further decreasing isoliquiritigenin content by 53%. However, salt stress increased liquiritin content by 43%, which might be a protective mechanism of salt-treated G. uralensis seedlings. Interestingly, G2 enhanced PAL activity by 27% whereas reduced trans-cinnamate 4-monooxygenase (C4H) activity by 43% which could inhibit lignin biosynthesis but promote flavonoid biosynthesis of salt-treated G. uralensis at the substrate level. G2 decreased shikimate O-hydroxycinnamoyltransferase (HCT) activity by 35%, increased CHS activity by 54% through up-regulating the gene Glyur000051s00003431 encoding CHS, and increased CHI activity by 72%, thereby decreasing lignin (34%) and liquiritin (24%) content, but increasing isoliquiritigenin content (35%), which could mitigate oxidative damage and changed salt-tolerance mechanism of G. uralensis.
盐分环境是对乌拉尔甘草（Glycyrrhiza uralensis Fisch.，简称乌拉尔甘草）生长的最大威胁之一，这是由过量活性氧（ROS）引起的氧化应激所致。黄酮类化合物是主要的药效成分，有助于维持乌拉尔甘草在盐分环境中的ROS稳态并减轻氧化损伤。为了研究内生蜡样芽孢杆菌G2是否能通过控制黄酮类生物合成来提高乌拉尔甘草的耐盐性，对在盐分环境中经G2处理的乌拉尔甘草进行了转录组和生理分析，重点关注黄酮类生物合成相关途径。结果发现，盐分通过在底物水平下调基因Glyur000910s00020578，使苯丙氨酸解氨酶（PAL）和4-香豆酸-CoA连接酶（4CL）的活性分别降低42%和39%，从而抑制黄酮类化合物的合成，进而由于基因Glyur006062s00044203和Glyur000051s00003431的下调，使查尔酮异构酶（CHI）和查尔酮合酶（CHS）的活性分别降低50%和42%，异甘草素含量进一步降低53%。然而，盐胁迫使甘草苷含量增加了43%，这可能是盐处理的乌拉尔甘草幼苗的一种保护机制。有趣的是，G2使PAL活性提高了27%，而反式肉桂酸4-单加氧酶（C4H）活性降低了43%，这在底物水平上可以抑制木质素生物合成但促进盐处理的乌拉尔甘草的黄酮类生物合成。G2使莽草酸O-羟基肉桂酰转移酶（HCT）活性降低了35%，通过上调编码CHS的基因Glyur000051s00003431使CHS活性提高了54%，并使CHI活性提高了72%，从而使木质素（34%）和甘草苷（24%）含量降低，但异甘草素含量增加（35%），这可以减轻氧化损伤并改变乌拉尔甘草的耐盐机制。
