Maybe going too far off topic here, but this is something I find super interesting. Carotenoids are broken down into a whole bunch of flavor compounds that are important not just in tomatoes but also watermelons, black tea, and wine.
Here’s a paper that goes into the parallel mutations in the carotenoid pathway of tomatoes and watermelons and how they affect flavor. Unfortunately it’s paywalled, but the summary is pretty informative.
https://www.sciencedirect.com/science/article/abs/pii/S0924224405001536
Right.
I wonder whether the pathways for creating astringency differ materially in Kaki and Virginiana.
And if so, is it possible that the C-PCNA or J-PCNA mutation will have no impact on the expression of astringency in DV? Would a DV x K hybrid therefore have to inherit the Kaki gene(s) responsible for creating astringency before the Kaki gene(s) responsible for eliminating astringency could function as usual?
@GrapeNut – You had some great insights above. Any thoughts here? Thx.
Evolutionarily speaking, it would be unlikely that the two persimmon species have different biosynthetic pathways for producing proanthocyanidins (the type of tannin responsible for astringency in persimmons). I think most, if not all, plants use variations on the same pathway to produce these compounds. What we should expect to differ are the various regulatory systems for each step of the pathway, and as a result, the ultimate composition and concentration of the final products.
From what I have read, there appears to be two mechanisms for loss of astringency in Asian persimmons: dilution and precipitation. Dilution is simply the consequence of fruit development. Most of a fruit’s growth happens from cell expansion. Water is pumped into cells formed shortly after fertilization, causing them to swell. As water content increases, anything present in the cells decreases in concentration if biosynthesis doesn’t keep up. Dilution occurs in all D. kaki, NA and A, the difference being that in Japanese PCNA persimmons, the Myb4 gene mentioned above fails to be expressed and the tannins formed early on get diluted until they are no longer perceptible to us. On the other hand, astringent persimmons continue to pump out tannins at a rate that exceeds the dilution effect.
https://link.springer.com/article/10.1007/s00425-010-1346-z
This paper found a correlation between cool temperatures after flowering, increased Myb4 expression, and consequently, higher tannin levels in PCNA cultivars. This suggests that the ast mutation affects Myb4 expression but isn’t on the gene itself and explains the phenomenon of astringency in PCNA cultivars grown in cool climates.
The precipitation mechanism is a bit more complicated. Tannins can only cause the astringent sensation if they are soluble. Under certain conditions, tannin molecules will bind to each other until they get so large they are no longer soluble and precipitate out of solution. This is (I think) the brown color in PVNA persimmons as well as the crud in the bottom of a red wine bottle. In persimmons, acetaldehyde molecules react with tannins, causing them to link together and precipitate. This occurs for astringent persimmons during the ripening process and for PVNAs slightly earlier.
The paper you linked above:
https://www.nature.com/articles/s41598-022-23742-4
and this paper:
https://onlinelibrary.wiley.com/doi/full/10.1111/tpj.15266
found that Chinese PCNAs have both mechanisms at work: some dilution due to reduced tannin production early on and increased acetaldehyde production prior to softening to precipitate the remaining tannins. It seems that another Myb gene, Myb14, both suppresses the tannin pathway (but doesn’t shut it off entirely) and upregulates genes that produce acetaldehyde. Because this would be a “gain of function” mutation that increases the effect of an existing gene, this may explain the dominant nature of inheritance. Myb14 should be present in all D. kaki, so the mutation likely affects how it is expressed.
To answer your question, if whatever gene is responsible for reduced D. kaki Myb4 expression can work on D. virginiana Myb4, there’s no reason why tannin production can’t be shut off early on, unless there are additional genes to switch on the pathway.
As for why methods to induce tannin precipitation don’t work in D. virginiana, I can think of three possible reasons. Purely speculative of course, and it’s possible the three work in concert:
1: The methods work, but without actually measuring the amount of insoluble vs soluble tannins, it’s impossible to know how well. It could be that American persimmons simply have too high of a concentration for the amount of acetaldehyde to completely neutralize. Simply tasting for astringency doesn’t really tell you how much is left.
2: American persimmons don’t produce a lot of acetaldehyde. I doubt anyone has measured the rate of loss of soluble tannins in American vs Asian persimmons. Could be that the process is a lot slower.
3. American persimmon genes for metabolizing acetaldehyde work more efficiently than Asian genes, reducing the effect on soluble tannins.
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Thanks. It’ll take time to process.
Meanwhile one quibble, maybe a matter of emphasis not substance: As we all agree, prior to dilution per se, in PCNA persimmons there is a reduction in the rate of production of astringent compounds. So PCNAs benefit from both low production and then dilution.
I guess you imply this when you say “the Myb4 gene mentioned above fails to be expressed and the tannins formed early on get diluted until they are no longer perceptible to us.” It’s just that the “two mechanisms” you set up at the outset (dilution and precipitation) omit this down-regulation of the production process.
Again, very helpful comments.
As far as I know, you are right that ethanol / acetaldehyde from PV seeds is responsible for the de-astringency and the brown color. My recollection is that the seeds produce ethanol and the flesh changes the ethanol into acetaldehyde, but please correct me if I have that wrong. Moreover I believe that the amount of ethanol produced by the seeds is dependent on the number of PV genes. So the gene impact is somewhat additive.
Meanwhile, I have been thinking along similar lines as you in #1-3 above, though you articulated the issues better than I could. Given a caveat that hybridizing species is always a crap-shoot, these issues have led me to worry that breeding a non-astringent PVNA Kaki x DV hybrid may require overcoming these obstacles. At minimum that would seem to imply a need for more PVNA genes in the hybrid than in a pure Kaki. Again, very speculative.
One item to add. DV seems to have at least one other mechanism that reduces tannins. jPCNA is from down-regulation of Myb4. cPCNA’s have some form of up-regulation of Myb14. An unknown but similar effect, likely another Myb?, causes varieties such as Morris Burton to have reduced astringency.
Pure speculation, but it looks like combining all three sets of genetics could totally re-write the persimmon astringency paradigm. It will take targeted genetic tests to ever achieve. “Just breeding persimmons” without a method to track the genes would be an exercise in futility. Hexaploid genome, 3 different but potentially complementary genes at least 2 of which are recessive, and relatively long generation times suggest it could be done in about 12 years with genetic tests but would take many lifetimes otherwise.
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We need know more about this. I’ve read such reports before, and I ordered scions of Morris Burton to graft this spring so that I could try it out. But the story seems to come and go. I’d expect a lot more excitement about the variety and about potential crosses with other DV names if it were observed reliably.
Do we know whether Morris Burton always loses astringency early? Does the loss depend on any known or possible environmental conditions, such as hot weather?
Anyway, my basic point is that if early loss of astringency in Morris Burton is reliable, we should be paying much more attention.
There are some things known about Morris Burton that could be very important. It is lighter colored, more yellow than orange. This indicates a change in the carotenoid biopath. The second is lowered astringency though I don’t know enough about it to say if the astringency is lost when fully ripe or if it is lost earlier in fruit development. The change to yellower color indicates the Beta Carotene step is interrupted somewhere much earlier in the sequence, maybe at phytoene. This is the step where tomatoes have more of a yellow/tangerine color. Perhaps not the same in persimmon, but it is intriguing to speculate.
You could almost put together a breeding plan where a cross involving Morris Burton, DV X DK hybrids, and cPCNA would result in a cold tolerant fruit that never develops astringency. It could be eaten any time the fruit got sweet but probably would be best when mature ripe. This would not require PV genetics because the tannin biopath would be disrupted at 3 stages before tannins form. Add in a requirement for large (apple size) fruit and you can see commercial potential.
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Are you concerned that low beta carotene might correlate with low flavor?
More generally, do we know where the product of flavor-producing compounds branches off from the production of astringent compounds?
If it were a white persimmon, I would be concerned about flavor. Since it is a yellow persimmon and I know of plenty of good flavored yellow fruits, I don’t think it will be a problem. This is just a guess and needs empirical proof.
I only have detailed knowledge about flavonoids from tomato, however, the biopaths involved are highly conserved in fruiting plants so it is likely similar in persimmon. There are over 400 known flavor compounds in tomato most of which are produced in the carotene and anthocyanin biopaths. One gene prevents accumulation of anthocyanins. One known gene shifts skin color from yellow to translucent along the way whacking a huge number of flavor compounds. Extending this to persimmon suggests there are hundreds of compounds in persimmon most of which can be increased or decreased.
- Sugar/sweet - arguably the most important, part of the starch biopath
- Acidity - probably second most important, part of the alkyl biopath (related to starch)
- Color - primarily from carotene and anthocyanin biopaths
- Umami - the unique flavor compounds our taste buds sense, hundreds of compounds involved
This begs a question why flavonoid biopaths are highly conserved. There are two closely related reasons. The first is that many flavor compounds do double duty protecting the plant from intense sun, pests, and diseases. The second is that getting seed spread is crucial for plant survival therefore attracting something to eat the fruit and spread the seed is a key trait. We can track these traits across many genera which infers the traits have been around for 10’s of millions of years.
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I’ve seen studies where the peak in tannins occurs before growth rate picks up and other studies where it peaks after. It’s difficult to monitor changes in both traits with enough precision. I don’t think it really matters in medium to large fruited cultivars though. The increase in fruit size is so great after tannin production shuts down in Japanese NA cultivars that whether it started with a high or low concentration of tannins becomes insignificant.
Acetaldehyde can be produced from ethanol as part of normal ethanol metabolism, just like in humans, or it can be produced from pyruvate. I believe genes from this second mechanism are upregulated in PVNA and Chinese PCNA cultivars. Post-harvest removal of astringency in persimmons makes use of the first mechanism.
A quick look at the table from this paper shows at least 8 compounds involved in persimmon flavor that can be derived from early steps of the flavonoid pathway. So yes, it’s possible that downregulating the pathway could impact flavor. However, there are multiple ways to get to these compounds, and it’s important to keep in mind that tannin biosynthesis uses the same starting molecules and potentially competes with the biosynthesis of some of these flavor compounds. So we really can’t say what the impact will be. In tomatoes, it seems that a lot of the monoterpenoids important for flavor come from the carotenoid pathway. Other plants have a dedicated monoterpene pathway. Persimmons don’t appear to have a lot of monoterpenes or norsioprenoids, the other aroma compound class that comes from carotenoids, so who knows.
I get the argument that plants evolve fruits that will be eaten to encourage seed dispersal, but probably it’s a two-way street. So the taste buds of animals evolved to find the chemical compounds that are useful to them flavorful. For example, two major sources of calories – sugars and fats – are very tasty. Ditto salt. Maybe flavor in fruits and vegetables is a proxy for vitamins, minerals, antioxidants, essential fatty acids, etc.
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Thanks again. Your reward for more information is more questions. 
The excerpted quote clarifies the PVNA process for me. Do you know where in the seed these reactions take place? Is it purely maternal tissue? I’ve wondered whether genes brought to the tree by the pollen can have a role. And does the acetaldehyde move into the flesh by an active or passive process?
Related to flavor, at least one of our members has said it is excellent, along with Lena and H63A and a few others… I trust those reviews from @Barkslip especially, because he has tasted so many different varieties.
Where I’m going with that, is that if color change is an important indicator for particular ripening /taste /astringency related traits @Fusion_power, I would surmise that Morris Burton may be a path to maintain excellent flavor.
I hope to add my input in a couple years if my grafting is successful this spring.
Which is why I used Morris Burton as an example above. It is highly likely a larger fruited Morris Burton offspring could set a new flavor and fruit production standard for persimmons.
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Unfortunately there’s not a lot of recent information on PVNAs, and the few papers I found were paywalled.
For Chinese PCNA cultivars I think it’s pretty clear that the reactions occur in the fruit pulp.
For PVNA cultivars, I don’t think we can say if the seed is producing ethanol/acetaldehyde or if the pulp is triggered to produce ethanol/acetaldehyde by the presence of seeds. Both ethanol and acetaldehyde are extremely soluble in fruit tissues and have no problem crossing cell walls or seed coats. The fact that tannin precipitation and ethanol/acetaldehyde concentrations are higher in the flesh surrounding seeds doesn’t tell us that it was the seeds that produced the compounds.
I wouldn’t get too hung up on the often-repeated “PVNA seeds produce ethanol” fact either. As far as I can tell, no one has followed up on the studies done in the 70s and 80s on PVNA persimmons. Just because they measured ethanol doesn’t mean that acetaldehyde isn’t the main molecule we should be concerned about. The enzymes work in both directions, and acetaldehyde is much more toxic than ethanol. It’s possible that whatever acetaldehyde doesn’t immediately react with tannins gets turned into ethanol to limit toxicity.
That said, ADH and PDC genes, the ones responsible for converting ethanol and pyruvate to acetaldehyde and back, are upregulated in the presence of abscisic acid in many plants. Abscisic acid is produced in seeds to induce embryo dormancy. I wonder if this may be the actual underlying mechanism for tannin precipitation in pollinated PVNA fruits.
I realize I oversimplified the mechanism behind the treatment methods to remove astringency in persimmons. It seems that the pyruvate to acetaldehyde pathway is induced as well in methods that deprive the fruit of oxygen.
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All of this makes total sense. Thanks again.
My only issue is the paragraph quoted immediately above. PVNA is a trait of some persimmons. Some others are PVA (which is like PVNA-lite). Most are just PCA. Presumably abscisic acid is produced by all persimmon seeds. Are you guessing that some varieties produce way more than others?
Whether this specific idea works or not, I like the general idea that seeds in PVNA fruit don’t produce ethanol or pyruvate themselves but rather they produce a substance that induces the flesh to produce one or both of those compounds.
Coincidentally, I’m planning to add Morris Burton too. I’ve already got H63-A, Barbra’s Blush, and Dollywood. Does anyone know if any of them produces pollen (e.g., male flowers)?
LOL, I guess we’ve drifted a long way from Ukraine!
Do we know if it [produces any pollen (e.g. male flowers)?
Don Compton has a bunch of Morris Burton crosses growing in his orchard from seed he got from James Claypool when James got too elderly to continue. They would have been row M in the Claypool orchard.
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There’s a lot more information on the Ukrainian breeding program in this thread roughly after post #159