Department of Plant Biology, University of Georgia, Athens, GA 30602, USA.
Department of Chemistry, University of Georgia, Athens, GA 30602, USA.
Plant Cell Physiol. 2020 Jan 1;61(1):64-75. doi: 10.1093/pcp/pcz178.
Plant cell wall polysaccharides, including xylan, glucomannan, xyloglucan and pectin, are often acetylated. Although a number of acetyltransferases responsible for the acetylation of some of these polysaccharides have been biochemically characterized, little is known about the source of acetyl donors and how acetyl donors are translocated into the Golgi, where these polysaccharides are synthesized. In this report, we investigated roles of ATP-citrate lyase (ACL) that generates cytosolic acetyl-CoA in cell wall polysaccharide acetylation and effects of simultaneous mutations of four Reduced Wall Acetylation (RWA) genes on acetyl-CoA transport into the Golgi in Arabidopsis thaliana. Expression analyses of genes involved in the generation of acetyl-CoA in different subcellular compartments showed that the expression of several ACL genes responsible for cytosolic acetyl-CoA synthesis was elevated in interfascicular fiber cells and induced by secondary wall-associated transcriptional activators. Simultaneous downregulation of the expression of ACL genes was demonstrated to result in a substantial decrease in the degree of xylan acetylation and a severe alteration in secondary wall structure in xylem vessels. In addition, the degree of acetylation of other cell wall polysaccharides, including glucomannan, xyloglucan and pectin, was also reduced. Moreover, Golgi-enriched membrane vesicles isolated from the rwa1/2/3/4 quadruple mutant were found to exhibit a drastic reduction in acetyl-CoA transport activity compared with the wild type. These findings indicate that cytosolic acetyl-CoA generated by ACL is essential for cell wall polysaccharide acetylation and RWAs are required for its transport from the cytosol into the Golgi.
植物细胞壁多糖，包括木聚糖、葡甘露聚糖、木葡聚糖和果胶，通常会发生乙酰化。尽管已经有一些生化特征被鉴定的负责这些多糖乙酰化的乙酰转移酶，但对于乙酰供体的来源以及乙酰供体如何被转运到高尔基体（这些多糖在那里合成）的了解甚少。在本报告中，我们研究了 ATP-柠檬酸裂解酶（ACL）在细胞壁多糖乙酰化中的作用，该酶生成细胞质乙酰辅酶 A，以及同时突变四个 Reduced Wall Acetylation（RWA）基因对拟南芥中乙酰辅酶 A 向高尔基体转运的影响。对不同亚细胞区室中产生乙酰辅酶 A 的基因的表达分析表明，负责细胞质乙酰辅酶 A 合成的几个 ACL 基因在束间纤维细胞中表达上调，并被次生壁相关转录激活因子诱导。证明 ACL 基因的表达同时下调会导致木聚糖乙酰化程度显著降低，木质部导管次生壁结构严重改变。此外，其他细胞壁多糖（包括葡甘露聚糖、木葡聚糖和果胶）的乙酰化程度也降低了。此外，从 rwa1/2/3/4 四重突变体中分离到的富含高尔基膜囊泡显示出与野生型相比乙酰辅酶 A 转运活性急剧降低。这些发现表明，ACL 产生的细胞质乙酰辅酶 A 是细胞壁多糖乙酰化所必需的，而 RWAs 是其从细胞质转运到高尔基体所必需的。
