The red color of red leaf lettuce is due to anthocyanin, a type of polyphenol pigment that is attracting attention for its antioxidant effects. Plants produce anthocyanins through a series of enzyme-driven reactions starting with the amino acid phenylalanine. In the process, this pathway produces a variety of flavonoids. Flavonoids are a broad category of plant compounds that serve many functions before some are ultimately converted to anthocyanins.
In the new study, researchers used genome editing to switch off the gene responsible for producing dihydroflavonol 4-reductase, an enzyme involved in a critical step just before anthocyanin formation in red lettuce. When this gene is disabled, plants no longer produce the characteristic red pigment.
Further analysis of the lettuce revealed another important change. Levels of several other flavonoids, including quercetin, were increased. This finding suggests that inhibiting anthocyanin production redirects the biochemical activity of the plant toward the accumulation of these other compounds within the flavonoid biosynthetic pathway.
No significant effect on plant growth
Despite the large changes in pigment and flavonoid composition, the modified lettuce showed no significant reduction in growth. This result suggests that it may be possible to alter the balance of flavonoids in lettuce by promoting the accumulation of precursor compounds instead of anthocyanins while maintaining normal growth and productivity.
Although researchers have not yet directly compared the engineered plants to traditional green lettuce varieties, red lettuce is already known for its high polyphenol production. As a result, this strategy may provide a promising way to develop lettuce varieties with customized functional components.
The researchers also note that flavonoid production is highly sensitive to environmental conditions such as light intensity and temperature. Because growers can carefully control these factors in plant factories, the findings could help support the development of specialized lettuce varieties optimized for indoor growing systems.
The Emen group’s research is funded by a grant from the Japan Science and Technology Agency’s “Open Innovation Platform Program for Businesses, Research Institutions, and Academia” (JSTOPERA, JPMJOP1851).
