Pré Martial, Caillet Victoria, Sobilo Julien, McCarthy James
Centre de Recherche Nestlé, 101 Av. Gustave Eiffel, Notre Dame d'Oé, BP 49716 - 37097 Tours, France.
Ann Bot. 2008 Aug;102(2):207-20. doi: 10.1093/aob/mcn076. Epub 2008 Jun 18.
Galactomannans act as storage reserves for the seeds in some plants, such as guar (Cyamopsis tetragonoloba) and coffee (Coffea arabica and Coffea canephora). In coffee, the galactomannans can represent up to 25 % of the mass of the mature green coffee grain, and they exert a significant influence on the production of different types of coffee products. The objective of the current work was to isolate and characterize cDNA encoding proteins responsible for galactomannan synthesis in coffee and to study the expression of the corresponding transcripts in the developing coffee grain from C. arabica and C. canephora, which potentially exhibit slight galactomannan variations. Comparative gene expression analysis was also carried out for several other tissues of C. arabica and C. canephora.
cDNA banks, RACE-PCR and genome walking were used to generate full-length cDNA for two putative coffee mannan synthases (ManS) and two galactomannan galactosyl transferases (GMGT). Gene-specific probe-primer sets were then generated and used to carry out comparative expression analysis of the corresponding genes in different coffee tissues using quantitative RT-PCR.
Two of the putative galactomannan biosynthetic genes, ManS1 and GMGT1, were demonstrated to have very high expression in the developing coffee grain of both Coffea species during endosperm development, consistent with our proposal that these two genes are responsible for the production of the majority of the galactomannans found in the grain. In contrast, the expression data presented indicates that the ManS2 gene product is probably involved in the synthesis of the galactomannans found in green tissue.
The identification of genes implicated in galactomannan synthesis in coffee are presented. The data obtained will enable more detailed studies on the biosynthesis of this important component of coffee grain and contribute to a better understanding of some functional differences between grain from C. arabica and C. canephora.
半乳甘露聚糖是某些植物种子的储存物质，如瓜尔豆（瓜尔豆属）和咖啡（阿拉伯咖啡和卡内弗拉咖啡）。在咖啡中，半乳甘露聚糖可占成熟生咖啡豆质量的25%，对不同类型咖啡产品的生产有显著影响。本研究的目的是分离和鉴定编码咖啡中负责半乳甘露聚糖合成的蛋白质的cDNA，并研究来自阿拉伯咖啡和卡内弗拉咖啡发育中的咖啡豆中相应转录本的表达，这两种咖啡豆可能表现出轻微的半乳甘露聚糖差异。还对阿拉伯咖啡和卡内弗拉咖啡的其他几种组织进行了基因表达比较分析。
利用cDNA文库、RACE-PCR和基因组步移技术获得两个假定的咖啡甘露聚糖合成酶（ManS）和两个半乳甘露聚糖半乳糖基转移酶（GMGT）的全长cDNA。然后生成基因特异性探针-引物组，并用于通过定量RT-PCR对不同咖啡组织中相应基因进行表达比较分析。
两个假定的半乳甘露聚糖生物合成基因ManS1和GMGT1在两种咖啡胚乳发育过程中的发育咖啡豆中均有很高的表达，这与我们提出的这两个基因负责咖啡豆中大部分半乳甘露聚糖的产生的观点一致。相比之下，所呈现的表达数据表明，ManS2基因产物可能参与绿色组织中半乳甘露聚糖的合成。
本文介绍了与咖啡中半乳甘露聚糖合成相关基因的鉴定。所获得的数据将有助于对咖啡豆这一重要成分的生物合成进行更详细的研究，并有助于更好地理解阿拉伯咖啡和卡内弗拉咖啡之间的一些功能差异。
