The art of blowing up protein

For an upcoming open-day we will extract DNA from strawberries. For this I made a slide that explains how DNA mutations lead to protein variants, than in turn lead to different phenotypes (redness in the strawberry's case). In doing this, I got fascinated by a strawberry cultivar called "Pineberry". But not because it is unpigmented, but because the reviews online say it is bland, which made me wonder whether an early pathway defect could affect both pigmentation and aroma. That is a hypothesis, not something taste reviews can establish.

Pigments

Here is the original biochemical speculation; I had not established the genetics of the cultivar.
Strawberry pigments are derived from two main chromophores (with a variety of glycosyl handles), both anthocyanins. Cyanidin derivatives tend towards a darker red, while pelargonidin derivatives give a brighter red. Cyanidin is not oxidised into pelargonidin: flavonoid 3′-hydroxylase acts upstream on precursor flavonoids, favouring the more hydroxylated cyanidin branch. (I found a nice graph of the spectra in a paper: here).

Original speculative schematic of three cultivars, not an established pathway or diagnosis of pineberry genetics. See the corrected chemistry in the text and the later evidence noted below.

Pineberries have little anthocyanin pigmentation in the flesh, but that does not by itself identify the faulty gene or distinguish a structural-enzyme defect from altered regulation. Naringenin is a colourless flavanone whose central ring lacks the extended conjugation of the anthocyanidins. Flavanone 3-hydroxylase acts early in a multistep pathway; it does not convert naringenin directly into cyanidin. Disrupting several different steps, or their regulation, could produce white fruit.

Taste

However, pigmentation should not affect taste. If anything the lack of anthocyanins should make it less bitter —not that strawberries are due to their sugar content. Yet, all the reviews online say it tastes bland. The name pineberry is because it tastes a bit like pineapple. A shared upstream disruption is one possible explanation, but flavour reviews do not establish that connection or show that naringenin is absent.

Strawberry flavour is caused by a panel of aromatic compounds. Several of which have strong strawberry smells by themselves, albeit with an artificial quality as is often found with aromatic compounds in isolation, e.g. isoamyl acetate is a banana aroma compound, but in isolation is causes the quintessential Nesquik fake banana flavour. Ethyl methylphenylglycidate is the compound used to imitate strawberries, while other distintive aroma compounds include benzyl acetate (strawberry/jasmin), p-Anisaldehyde (floral/aniseed), furaneol (strawberry/pineapple) along with the usual fruity short fatty acid acetate esters. Furaneol is not produced from cinnamic/cumaric acid, while the other are, and is a compound described as smelling like pineapple. As pineberries taste like pineapple, I would bet they can still make furaneol fine, while the levels of the other compounds are affected. The pigments, as mentioned, are anothocyanins, which are derived from naringenin, which is formed by condensing a polyketide that has a cinnamic acid component.

Benzyl acetate is also produced from cinnamic acid. Actually, I mentioned cinnamoyl-CoA in the whatif/Breaking Bad/synbio post about methamphetamine biosynthesis—back when Breaking Bad still aired...
The ethyl methylphenylglycidate looks complicated, but if you look at it, you can see that the backbone is an ethyl cinnamate that has been given a methyl group. It is rather unusual and I did not find any biosynthetic pathways in a quick glance, but to get an epoxyl you need an allylic alcohol so my guess is that it was not methylated but was hydroxylated first then an allyl group added somehow (decarboxylation?) or via radical SAM dependent methylation. Nevertheless, the cinnamic acid is the key part that is possibly missing.

Cinnamic acid and coumaric acid are generally produced by a dedicated phenylalanine amonia-lyase and tyrosine ammonia-lyase, but often coumaric acid is produced by 4-cinnamic acid hydroxylase from cinnamic acid. Phenylalanine ammonia-lyase was therefore my speculative candidate, but this is not evidence that it causes the white phenotype. Later genetic work on white strawberries identified MYB10 regulatory variation as a major determinant of fruit colour; that does not diagnose this particular pineberry cultivar or its flavour. See the 2020 study.