FveIPT2 boosts strawberry colour, aroma and antioxidants

A little-known category of plant genes is often regarded by biologists as little more than background noise.

These are known as housekeeping genes, and their role is to keep cells functioning.

Scientists generally view them as passive: permanently active, performing the same tasks and largely irrelevant to metabolic engineers.

One research group, however, put that broad assumption to the test. It selected a woodland strawberry gene that had received almost no attention in flavour or nutrition studies.

The researchers increased its activity by roughly 50-fold and observed the fruit’s response.

An unlikely FveIPT2 candidate

The gene under investigation, FveIPT2, falls within a plant-gene category that biologists have mostly discounted.

Researchers typically examine housekeeping genes to learn what occurs when they fail, which usually results in cell death.

Beyond that, they are generally treated as routine genes carrying out routine work. Cytokinins, plant hormones that control growth, branching and flowering, show a comparable divide.

Some enzymes involved in producing these hormones actively direct plant development. Others, including FveIPT2, seem merely to maintain background processes.

Dr Lijun Gan of Nanjing Agricultural University (NJAU) led the work alongside Dr Yi Li of the University of Connecticut (UConn).

Major rise in the gene’s output

The researchers engineered strawberry plants to overexpress FveIPT2, making the gene operate at far higher levels than usual.

They tested two modified lines alongside wild plants under equivalent conditions.

In one line, the gene operated around eight times more strongly than in the controls. In the other, it reached almost 49 times the normal level, far beyond what an unmodified plant would ordinarily produce.

The team then monitored the plants as they developed. They flowered at the expected time, and fruit set occurred as scheduled.

Externally, the modified plants were indistinguishable from the wild plants.

Richer fruit with comparable yields

The first unexpected result was what did not happen. After 40 days and again after six months, the modified plants were the same size and appearance as their wild counterparts.

Individual fruit weight, berry size and sugar content were all unchanged.

The second surprise came from the analysis of fruit chemistry. Total anthocyanins increased by 34 percent in the line with higher expression.

Total flavonoids and phenolics also increased together. The fruit even appeared a slightly deeper red.

Those improvements did not reduce growth or sweetness. The combination of increased antioxidants, unchanged yields and similar sweetness was unexpected.

Anthocyanin levels surge

Metabolite results revealed the true scale of the effect. Among 1,058 compounds identified in ripe fruit, nearly seven hundred differed between modified and wild plants.

Nine individual anthocyanins rose substantially. Cyanidin chloride reached 18 times the wild-type level.

A different cyanidin variant was nearly ten times higher. Pelargonidin chloride rose to almost seven times its previous level.

These substances do more than provide colour. Anthocyanins are antioxidants, and one published review associates them with a reduced risk of cardiovascular and neurodegenerative disease in humans.

The genes responsible for making these compounds, along with the regulators that activate the pathway, were all more active in the modified fruit.

Sweeter aroma and less turpentine

Colour is not the entire story, as strawberries owe much of their appeal to their scent.

Of the 47 terpenoids measured by the team, 24 increased. The two largest rises were each more than tenfold.

Linalool, which gives strawberries sweet, floral notes, increased sharply.

Levels of α-pinene, a compound that lends lower-quality berries a resinous, turpentine-like note, fell noticeably.

Earlier tomato research showed that metabolic engineering could increase linalool, but it improved aroma only rather than pigment. This team achieved both effects using just one gene.

A concealed biological pathway

The researchers anticipated that the cascade would follow the usual cytokinin signalling route, but that did not happen.

That pathway should have activated specific marker genes, which switch on when cytokinin hormones become active.

Yet the team found that these genes decreased rather than increased.

Whatever FveIPT2 does, the standard hormone pathway may therefore not be the principal force behind the result.

The gene’s normal function is basic cell maintenance: modifying molecules that help cells produce proteins.

This housekeeping function may be influencing fruit chemistry through a mechanism that entirely bypasses conventional hormone signalling.

Beyond woodland strawberries

The experiments used woodland strawberry, a model plant developed for laboratory work rather than commercial cultivation.

It remains untested whether the same outcome applies across other commercial varieties.

Exactly how FveIPT2 produces these chemical shifts is also still unknown.

Although the researchers excluded the obvious hormone route, they have not yet identified the overall driver of the effect.

A new genetic lever

For the first time, a housekeeping gene of this kind has been demonstrated to improve fruit chemistry without damaging the plant.

“By targeting a tRNA-type gene rather than classical hormone regulators, we were able to improve fruit color, aroma, and nutritional compounds without the growth penalties that often accompany metabolic engineering,” said Gan.

This offers breeders another lever to use. Strawberry breeding programmes seeking deeper colour, fuller aroma and more antioxidants may no longer need to accept lower yields.

Should similar genes act in the same manner in apples, peaches or grapes, the available toolbox could expand considerably.

Genes once overlooked could prove to be among the most valuable breeding targets that fruit science has yet to explore fully.