Table_8_Glycinebetaine Biosynthesis in Response to Osmotic Stress Depends on Jasmonate Signaling in Watermelon Suspension Cells.XLS

Glycinebetaine is an important non-toxic osmoprotectant, which is accumulated in higher plants under various stresses. The biosynthesis of glycinebetaine achieved via is a two-step oxidation from choline and betaine aldehyde, catalyzed by choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH), respectively. Up-regulated gene expression of BADH and CMO induced by stress is clearly observed, but the signal transduction is poorly understood. Here, glycinebetaine accumulation in response to osmotic stress and growth recovery induced by exogenous glycinebetaine were observed in a watermelon cell line. When tracing back to the genome sequence of watermelon, it shows that there exists only one member of ClCMO or ClBADH corresponding to glycinebetaine biosynthesis. Both genes harbor a CGTCA-motif in their promoter region which is involved in methyl jasmonate (MeJA)-responsiveness. Amongst MeJA, Ethephon, abscisic acid (ABA), and salicylic acid (SA), MeJA was most effective in gene inducing the expression of ClCMO and ClBADH, and the accumulation of glycinebetaine could also reach an amount comparable to that after osmotic stress by mannitol. Moreover, when ibuprofen (IBU), a JA biosynthesis inhibitor, was pre-perfused into the cells before osmotic stress, glycinebetaine accumulation was suppressed significantly. Interestingly, newly grown cells can keep a high content of glycinebetaine when they are sub-cultured from osmotic stressed cells. This study suggests that osmotic stress induced glycinebetaine biosynthesis occurs via JA signal transduction and not only plays a key role in osmotic stress resistance but also contributes to osmotic stress hardening.

甘氨酸甜菜碱（Glycinebetaine）是一类重要的无毒渗透保护剂，可在多种胁迫条件下于高等植物中积累。甘氨酸甜菜碱的生物合成通过两步氧化反应完成：以胆碱与甜菜碱醛为底物，分别由胆碱单加氧酶（CMO）和甜菜碱醛脱氢酶（BADH）催化。已有研究明确观察到胁迫可诱导BADH与CMO的基因表达上调，但相关信号转导机制仍不甚明晰。本研究以西瓜细胞系为材料，对渗透胁迫响应下的甘氨酸甜菜碱积累以及外源甘氨酸甜菜碱诱导的生长恢复现象进行了观测。对西瓜基因组序列的溯源分析显示，仅存在分别对应甘氨酸甜菜碱生物合成的一个ClCMO基因拷贝与一个ClBADH基因拷贝。二者的启动子区域均含有与茉莉酸甲酯（MeJA）响应相关的CGTCA基序。在茉莉酸甲酯、乙烯利、脱落酸（ABA）以及水杨酸（SA）这四种信号分子中，茉莉酸甲酯对ClCMO和ClBADH基因表达的诱导效果最为显著，其介导的甘氨酸甜菜碱积累量亦可达到甘露醇渗透胁迫处理后的水平。此外，若在渗透胁迫处理前向细胞中预灌注茉莉酸（JA）生物合成抑制剂布洛芬（IBU），甘氨酸甜菜碱的积累会被显著抑制。值得注意的是，从渗透胁迫处理的细胞中继代培养得到的新生细胞，仍可维持较高水平的甘氨酸甜菜碱含量。本研究表明，渗透胁迫诱导的甘氨酸甜菜碱生物合成依赖于JA信号转导通路，该通路不仅在渗透胁迫抗性中发挥关键作用，同时还可介导渗透胁迫的适应性硬化。