Abstract
Sunflower (Helianthus annuus L.) sprouts accumulate high amounts of caffeoylquinic acids (CQAs) including chlorogenic acid (5-CQA) and 1,5-diCQA. These compounds, which can be found in many plants, including tomato, globe artichoke, and chicory, have many health benefits, including antioxidant, antihepatotoxic, and antiglycative activities. However, CQA profiles and biosynthesis have not previously been studied in sunflower sprouts. In the present study, we found that 5-CQA and 1,5-diCQA were the major CQAs found in sunflower sprouts. We also identified minor accumulation of other CQAs, namely 3-CQA, 4-CQA, 3,4-diCQA, and 4,5-diCQA. According to genome-wide identification and phylogenetic analysis of genes involved in CQA biosynthesis in sunflower, three genes (HaHQT1, HaHQT2, and HaHQT3) encoding hydroxycinnamoyl CoA:quinate hydroxycinnamoyl transferase (HQT) and two genes (HaHCT1 and HaHCT2) encoding hydroxycinnamoyl CoA:shikimate/quinate hydroxycinnamoyl transferase (HCT) were identified. Expression analysis of these five genes in hypocotyls and cotyledons strongly suggested that HaHQT2 could be the main enzyme responsible for CQA biosynthesis, as HaHQT2 had the highest expression levels. In addition, when transiently expressed in the leaves of Nicotiana benthamiana, all three HaHQTs, which were soluble and not membrane-bound enzymes, could increase the content of 5-CQA by up to 94% compared to that in a control. Overall, our results increase understanding of CQA biosynthesis in sunflower sprouts and could be exploited by plant breeders to enhance accumulation of health-promoting CQAs in these plants.
Highlights
Increased health consciousness among consumers and concerns about the negative health effects of chemical preservatives used in the food industry has led to increase an interest in natural and herbal substances
We report the identification and functional characterization of key genes involved in caffeoylquinic acids (CQAs) biosynthesis in sunflower sprouts
The levels of 1,5-dicaffeoylquinic acid (diCQA) and 4,5-diCQA did not show any significant differences between the infiltrated leaves versus the control. These results indicated that all HaHQTs were involved in CQA biosynthesis
Summary
Increased health consciousness among consumers and concerns about the negative health effects of chemical preservatives used in the food industry has led to increase an interest in natural and herbal substances. Fruits and vegetables accumulate a wide range of bioactive compounds with many health-promoting benefits. Among these bioactive compounds, phenolics are of high importance, and caffeoylquinic acids (CQAs) comprise one of the most common phenolic groups. When caffeoyl moieties combine with quinic acid, CQAs are formed. These CQAs can be categorized into various groups based on the position, number, and identity of their acyl group. The monocaffeoylquinic acid (monoCQA) group includes 1-CQA, 3-CQA (known as neochlorogenic acid), 4-CQA (known as cryptochlorogenic acid), and 5-CQA (known as chlorogenic acid). The dicaffeoylquinic acid (diCQA) group includes 1,3-diCQA, 1,4-diCQA, 1,5-diCQA, 3,4-diCQA, 3,5-diCQA, and 4,5-diCQA (Figure 1)
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