Scientists look for the "vine" aroma in strawberries

why does strawberry have its own taste and smell? In this blog post, Professor Kevin M. Folta discusses a recent study he published on BMC Plant Biology. The study "declassified" the final step in the synthesis process of methyl anthranate (MA), a natural compound found in many ripe fruits, in cultivated strawberries.images are from the original
the grape flavor added to the cough syrup makes it easier to swallow. Grape-flavoured carbonated beverages have a grape-flavored taste and work as a sweet molecule. In food chemistry, this familiar source of sticky sweetness is interesting, and what we're revealing now is the genetic basis for the molecular origin that causes fruity tastes to be produced under natural conditions, even in fruity fruits like strawberries that don't taste grape.
we get a familiar "grape" taste from food, thanks to a compound called phthalates (MA). The compound was first used as a synthetic artificial grape flavoring, commonly found in fruity beverages, perfumes and other common consumer products. It is the taste represented by purple and is also a bird repellent (a chemical reagent to prevent bird invasion).
many fruits also contain natural phthalates when ripe. It is an iconic scent of Vitis labrusca. Among other fruits, MA plays an auxiliary role, playing an auxiliary role in the first stage of fruit digestion - mechanical rupture in the mouth (commonly known as big bites) - and playing a small note in the scattered compound symphony. Sugar and acid form the basis of the taste perceived by the tongue, while a group of volatile compounds rush directly to the olfactory receptor from behind the palate, triggering nerve signals that the brain perceives after milliseconds.
the presence of heart-brain connections makes MA reminiscent of summer, desserts and healthy snacks. That's why fruit taste is so important -- if scientists can make it taste better, it could inspire consumers to choose healthier diets and bring better benefits to growers.
in modern varieties, taste is not always a top priority. Growers will focus on varieties that are resistant to disease, have high yields, are large, and can still look basically satisfactory after a long journey. Decades of high-intensity artificial selection of fruits such as strawberries have led to a decline in their sensory quality.
, MA is found in wild strawberries, but it no longer exists in almost all modern varieties. It is now found only in a few older varieties and in new varieties specifically designed for the aroma of grapes.
interest in our lab is finding the genes needed to synthesize important volatile flavor substances so that they can be reintroduced into new varieties. If we identify the genes needed in the synthesis process, we can develop DNA tags to speed up the culture process.
our study was published by Pillet et al.
paper. The study first found the gene in a complex way, and then identified the last gene in catalytic MA synthesis. The work used genomics, genetics, gene expression analysis, and strawberries poked in by syringes.
, the varieties that produce MA and 2000s that do not produce MA are hybridized. We found that their offspring were separated in whether they produced aromatic compounds: some had aromatic compounds, some did not. We analyzed the fruits from each offspring plant to get a preliminary understanding of the active genes corresponding to MA (inferred from the RNA level).then we combine all sequences of the genes expressed by the strawberries that produce MA into one list, and all the genomes expressed in strawberries that do not produce MA are synthesized into another list. Comparing the two lists by calculation, it was found that only five genes were apparently activated in the strawberries that produced MA, while those that did not produce MA were silenced.
one of these genes is responsible for encoding methyl transferase. Methyl transferase, as the name implies, is responsible for the transfer of methyl, and MA is phthalates also have methyl. The job of this enzyme is basically to grab phthalates and glue them to produce phthalates.
we tested this hypothesis in several ways. First, we used RNA interference technology to turn off this gene in the fruit that produces MA. We inject bacteria into the flesh, and these bacteria are able to transfer the reverse copy of the gene to the cells. The newly injected reverse gene inhibits the methyl transferase gene. After these operations, the fruit no longer produces MA. This is very powerful evidence that it is this gene that drives the synthesis process. Once the methyl transferase gene is turned off, the fruit no longer produces MA.
The second test is to produce the enzyme in bacteria, purify it, and then determine whether the synthase can act on methyl-supply compounds, strip methyl and move it to phthalates molecules to obtain phthalates. But the experiment didn't work, and there are many technical reasons for it.
, however, if bacteria produce the enzyme themselves and then add phthalates to their mediums, these bacteria can produce phthalates. In another test, we used frozen fruit powder to re-make it into a chemical soup containing phthalates and methyl feeds. These fruit powders can also be synthesized from this chemical soup to produce a grape-scented MA! Fruit powder cannot produce MA if any of the ingredients are missing from the soup.
, we used genomics and genetic methods to find candidate genes that might perform the final step in MA synthesis. If the gene is turned off, MA is not detected. The enzymes that correspond to it can make MA in bacteria, and when we add the correct preaphases to strawberry flesh, we can produce MA. All this data led us to believe that methyl transferase was indeed the right gene in the process!
the last step is to determine that there is a significant difference in this gene between the fruit that produces MA and the fruit that does not produce MA. We found that part of the gene-controlled region can amplification in fruits that produce MA, but not in fruits that do not produce MA. This DNA sequence can be used as a "molecular marker". Now, whoever wants to breed strawberries for the purpose of producing a high level of MA should first test their plants for an active version of the gene. This makes it more likely that future generations will be able to produce MA.
think the story of MA and Strawberry is over, you're wrong. Our study also shows that MA levels depend on environmental conditions and the ripening stage of the fruit. This is good news for us because it means that more genes are involved in the process, so research will continue.
the future, plant breeders will be able to combine genetics to produce a super-powerful strawberry if genes that encode each flavor can be identified. This delicious berries will reawaken the long-lost taste stimulation of the ancient varieties and perfectly match the needs of modern production. (Source: Science.com)