School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI 49931, USA.
BMC Plant Biol. 2009 Dec 29;9:151. doi: 10.1186/1471-2229-9-151.
Phenylpropanoid-derived phenolic glycosides (PGs) and condensed tannins (CTs) comprise large, multi-purpose non-structural carbon sinks in Populus. A negative correlation between PG and CT concentrations has been observed in several studies. However, the molecular mechanism underlying the relationship is not known.
Populus cell cultures produce CTs but not PGs under normal conditions. Feeding salicyl alcohol resulted in accumulation of salicins, the simplest PG, in the cells, but not higher-order PGs. Salicin accrual reflected the stimulation of a glycosylation response which altered a number of metabolic activities. We utilized this suspension cell feeding system as a model for analyzing the possible role of glycosylation in regulating the metabolic competition between PG formation, CT synthesis and growth. Cells accumulated salicins in a dose-dependent manner following salicyl alcohol feeding. Higher feeding levels led to a decrease in cellular CT concentrations (at 5 or 10 mM), and a negative effect on cell growth (at 10 mM). The competition between salicin and CT formation was reciprocal, and depended on the metabolic status of the cells. We analyzed gene expression changes between controls and cells fed with 5 mM salicyl alcohol for 48 hr, a time point when salicin accumulation was near maximum and CT synthesis was reduced, with no effect on growth. Several stress-responsive genes were up-regulated, suggestive of a general stress response in the fed cells. Salicyl alcohol feeding also induced expression of genes associated with sucrose catabolism, glycolysis and the Krebs cycle. Transcript levels of phenylalanine ammonia lyase and most of the flavonoid pathway genes were reduced, consistent with down-regulated CT synthesis.
Exogenous salicyl alcohol was readily glycosylated in Populus cell cultures, a process that altered sugar utilization and phenolic partitioning in the cells. Using this system, we identified candidate genes for glycosyltransferases that may mediate the glycosylation, and for transporters that mediate the subcellular compartmentalization of sugars and phenolic glycosides. The suspension cells appear to represent a facile system for dissecting the regulation of phenolic carbon partitioning, and in turn, its effects on growth in Populus.
苯丙素衍生的酚糖苷（PGs）和缩合单宁（CTs）是杨树中庞大的、多用途的非结构性碳汇。在几项研究中观察到 PG 和 CT 浓度之间存在负相关。然而，这种关系的分子机制尚不清楚。
在正常条件下，杨树细胞培养物产生 CTs 而不产生 PGs。水杨醇的喂养导致最简单的 PG 之一——水杨苷在细胞中积累，但不会积累更高阶的 PG。水杨苷的积累反映了糖基化反应的刺激，该反应改变了许多代谢活动。我们利用这个悬浮细胞喂养系统作为分析糖基化在调节 PG 形成、CT 合成和生长之间代谢竞争中可能作用的模型。水杨醇喂养后，细胞以剂量依赖的方式积累水杨苷。较高的喂养水平导致细胞 CT 浓度降低（在 5 或 10 mM 时），并对细胞生长产生负面影响（在 10 mM 时）。水杨苷和 CT 形成之间的竞争是相互的，并且取决于细胞的代谢状态。我们分析了对照组和用 5 mM 水杨醇喂养 48 小时的细胞之间的基因表达变化，此时水杨苷积累接近最大值，CT 合成减少，对生长没有影响。一些应激响应基因上调，提示喂养细胞中存在一般应激反应。水杨醇喂养还诱导了与蔗糖分解、糖酵解和三羧酸循环相关的基因表达。苯丙氨酸解氨酶和大多数类黄酮途径基因的转录水平降低，与 CT 合成下调一致。
外源水杨醇在杨树细胞培养物中很容易被糖基化，这一过程改变了细胞中糖的利用和酚类物质的分配。利用该系统，我们鉴定了可能介导糖基化的糖基转移酶候选基因，以及可能介导糖和酚糖苷亚细胞区室化的转运蛋白候选基因。悬浮细胞似乎代表了一种易于剖析酚类碳分配调节及其对杨树生长影响的系统。
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