Chlorogenic acid synthesis in coffee: An analysis of CGA content and real-time RT-PCR expression of HCT, HQT, C3H1, and CCoAOMT1 genes during grain development in C. canephora

Abstract

The mature coffee grain contains a high level of chlorogenic acids (CGA). We have quantified the main caffeoylquinic acids (CQA) and dicaffeoylquinic acids (diCQA) in Coffea canephora (robusta) grain during late development. This analysis indicates the CQA levels remain relatively steady during the final stages of grain development, but the levels of diCQA fall significantly. Analysis of quinic acid, a key CGA precursor in coffee, shows it is present at a high level in the early grain, but then drops to a low level as development progresses. To better understand coffee CGA synthesis, and to learn why diCQA and quinic acid levels fall late in grain development, we have cloned cDNA encoding four key enzymes for CGA synthesis in coffee; HCT, HQT, C3H1 and CCoAOMT1. The characterization of recombinant HCT, HQT and CCoAOMT1 proteins is also described. Quantitative real-time RT-PCR data is presented for different stages of grain and pericarp development, as well as several other C. canephora tissues. Elevated HCT and CCoAOMT1 expression in branch tissues strongly suggests the products of these genes are associated with increased lignin synthesis, while higher HQT expression appears to be more closely correlated with CGA accumulation. The data presented forms an important base for designing new experiments aimed at improving our understanding of CGA synthesis in coffee and other plants, and could facilitate the development of new strategies to increase the CGA content of plant foods.