Center for Plant Environmental Stress Physiology, Department of Horticulture and Landscape Architecture, Purdue University, 625 Agriculture Mall Dr., West Lafayette, IN 47907-2010, USA.
Phytochemistry. 2010 Mar;71(4):404-14. doi: 10.1016/j.phytochem.2009.11.002. Epub 2009 Dec 11.
Glycinebetaine (GB) is a compatible solute that is accumulated by some plant species, especially under conditions leading to tissue osmotic stress. Genetic modification for accumulation of GB in an attempt to produce more stress tolerant plants has been a focus for several groups in recent years. However, attempts to increase tissue GB concentrations have been unsuccessful, with many transgenic lines accumulating far lower concentrations than naturally-occurring GB accumulators. A better understanding of the metabolic regulation of GB synthesis is necessary for successful molecular breeding and biotechnology. We utilized previously developed near-isogenic lines for GB accumulation to characterize the biochemical basis for GB deficiency in maize and sorghum. Salinity resulted in increased accumulation of choline in both accumulating and non-accumulating lines. When grown in the presence of NaCl, GB-non-accumulating lines had increased concentrations of choline and phosphocholine, but not GB. Decreased GB synthesis can be explained from the increased concentrations of phosphocholine in planta and the strong inhibition of N-phosphoethanolamine methyltransferase by phosphocholine observed in vitro. The lack of GB accumulation in GB-/- homozygous NILs was not due to the lack of the putative choline monooxygenase (the enzyme responsible for choline oxidation to betaine aldehyde) gene or protein that we describe. The previously identified bet1 locus does not appear to be choline monooxygenase. However, the lack of GB synthesis does affect the synthesis and turnover of choline moieties in GB non-accumulating lines, which may lead to alterations in overall 1-carbon metabolism in plants.
甘氨酸甜菜碱（GB）是一种相容性溶质，被一些植物物种积累，尤其是在导致组织渗透胁迫的条件下。近年来，许多研究小组一直致力于通过遗传修饰来积累 GB，以试图生产更能耐受胁迫的植物。然而，试图增加组织 GB 浓度的尝试并不成功，许多转基因系积累的 GB 浓度远低于自然积累的 GB 积累物。为了成功进行分子育种和生物技术，需要更好地了解 GB 合成的代谢调控。我们利用先前开发的近等基因系来积累 GB，以表征玉米和高粱中 GB 缺乏的生化基础。盐胁迫导致积累和非积累系中胆碱的积累增加。当在 NaCl 存在下生长时，GB 非积累系中胆碱和磷酸胆碱的浓度增加，但 GB 浓度没有增加。体内磷酸胆碱浓度的增加以及体外观察到磷酸胆碱对 N-磷酸乙醇胺甲基转移酶的强烈抑制，可以解释 GB 合成减少的原因。在 GB-/-纯合近等基因系中缺乏 GB 积累并不是由于缺乏我们描述的假定胆碱单加氧酶（负责胆碱氧化为甜菜碱醛的酶）基因或蛋白所致。先前鉴定的 bet1 基因座似乎不是胆碱单加氧酶。然而，GB 合成的缺乏确实会影响 GB 非积累系中胆碱部分的合成和周转，这可能导致植物中 1 碳代谢的整体改变。
