Transposons and Double Chinas

I was looking for something else … but I do a lot of that.

Sci Rep. 8: 12912 (2018)
A miR172 target-deficient AP2-like gene correlates with the double flower phenotype in roses
François, et al.

The title says it all. “In the double flower rose, two alleles of RcAP2L are present, one of which harbours a transposable element inserted into intron 8. This insertion leads to the creation of a miR172 resistant RcAP2L variant.”

And it goes on like that. It is all well and good, so far as it goes. It does leave lots of room for double-flowered roses that are not descended from the Chinas. Some of these cannot be persuaded to increase the number of petals, suggesting that there may be a different type of doubling for ‘Gloire des Rosomanes’, ‘Trigintipetala’, the Rose of Miletus with brilliant color and no more than a dozen petals (possibly the Holosericea), and the Tuscan roses.

Then there was the ‘Centifolia’ of Pliny the Elder, and the Nabateans. That was possibly a selected form of our Rosa Alba, and probably one parent of the Dutch Centifolias, which owe the rest of their qualities to the Damasks.

The authors also did not include ‘Marechal Niel’ or ‘Alexander Hill Gray’, which seem to have inherited the excessive doubling from Parks’ (white and) yellow China rose. Has any other diploid China rose packed together so many petals?

The matter of doubling is a puzzle. I’m pretty sure the China roses had nothing to do with the double-flowered forms of Rosa arkansana.

And it is a strange fact that doubling can turn up in the progeny of interspecific hybrids, where doubling was not seen anywhere else among the parental species.
Vilmorin’s Argemone Hybrids (1913)
Pfitzer: Improving tuberous begonias, gladioli and Salvia (1911)

I recall reading about a double-flowered Plum-Peach hybrid (19th century), but don’t have the link. And someone should have a look at double-flowered Petunias to explain the weirdness Mrs. Francis observed.
Francis: Double Seeding Petunias (1915)

There is more pathway to double-flowering. I forgot where I read it. Likely in a paper.

What is really important to know is this in breeding: Single and semi-double are genetically little different, so don’t expect a single x double or semi-double x double to result in much difference if all other genetic factors are the same. However, do expect that doubling can vary wildly. There is a paper on this out there somewhere in the ether.

It might be exceptional, but at least some single-flowered R. setigera appear to be capable of producing very double seedlings when used as the seed parent, sometimes even if the pollen parent isn’t overly double.

I wonder if the regulation of producing stamens instead of petals isn’t just easily overcome by way of gene mutation or silencing, similar to the regulation of once-flowering behavior.

Synstylae types, even as modern as Yellow Brick Road, can cause progeny to produce an excessive amount of male parts into petals – often leading to quartering effect.

That’s true–I’ve seen more than a few very double seedlings from YBR (I don’t know if I would guess that the effect is solely attributable to Synstylae background). Apparently R. bracteata (among non-Synstylae) can also produce highly double seedlings in the first generation, considering ‘Maria Leonida’. There are probably others, too.

“Rosa sect. Bracteatae (one of two species sampled) and R. sect. Laevigatae (monospecific) are resolved as close relatives of the Synstylae clade, and our nuclear GAPDH sequences suggest that they form a distinct lineage.” -‘Phylogeny and biogeography of wild roses with specific attention to polyploids’

I will try to find doubling papers later this week. My brain is spaghetti right now lol.

I think we should consider the doubling factor as working on a proportion of the potential stamens rather than than as strictly numerical increase. For example, Erlanson spent some of her time counting stamens. Rosa setigera ranged from 185 to 220 (average 205). That’s the highest count among the American species, and just a bit more than R. palustris, 170-200. We may guess that R. blanda (85-140) would yield hybrid offspring with more petals than R. woodsii (35-85) offspring when bred to the same double-flowered parent.

And while were at it, ‘Champneys’ Pink Cluster’ and ‘Blush Noisette’ have more petals than ‘Old Blush’.

Canalization may come into play, but that’s a subject that cannot be explained in a few lines. Some single-flowered varieties, like ‘Mutabilis’, will tease us with the occasional extra petal, or a couple of petaloids. These cooperative types nat allow greater expression of the doubling factor.

‘Dainty Bess’ is also a bit of a tease.
Moe & Kristofferson: Temp & Light & Roses (1969)
The number and the size of the petals decreased significantly with increasing temperature,
Semeniuk: An effect of temperature on development and differentiation of rose flowers. (1964)
The maximum number of petals was formed at 62°, while at 82° and 92°F the number of petals was reduced to 5, the basic number in wild rose species

Moe & Kristofferson worked with ‘Baccara’, while Semeniuk used five seedlings of ‘Ma Perkins’. All of these probably inherited the doubleness from the Chinas. So, in this case, the effect of the transposon is reduced at high temperatures. I have no idea how doubling inherited from other sources would be affected … if at all.

I guess I do know something about the interactions among different types of doubling.

‘Schoener’s Nutkana’ bears single flowers even though the pollen parent (Paul Neyron) is very double. It looks to me like Rosa nutkana blocked the China-rose doubling. But when Schoener’s rose was crossed with the HT ‘Souv de Mme Boullet’, the result was the very double (and VERY large) ‘Leonard Barron’.

Budd (1897) reported on the rose ‘I.A.C’, raised from a cross of a 5-petal Russian Rugosa and ‘General Jacqueminot’.
“A peculiarity of this variety is that it has twenty-one more petals than its two parents combined.”

Apparently, the not-too-double trait of ‘Gloire des Rosomanes’ was dominant over the China-rose doubling that filled out ‘I.A.C.’.

But I’m just guessing.

If you go look at my photos of ‘Miracle on the Hudson’ on HMF, you’ll find what temperate rainforest conditions can do to it.

We propose that RhAG plays an essential role in rose flower patterning by regulating petal development, and that low temperatures increase petal number, at least in part, by suppressing RhAG expression via enhancing DNA CHH hypermethylation of the RhAG promoter.”

  • ‘Low temperature-induced DNA hypermethylation attenuates expression of RhAG, an AGAMOUS homolog, and increases petal number in rose (Rosa hybrida)’

More transposon and doubling:
Sci Rep. 8: 12912 (2018)
A miR172 target-deficient AP2-like gene correlates with the double flower phenotype in roses
François et al.

In this study, we identified a gene of the euAP2 family, RcAP2L , that localizes within the double flower interval. We identified a truncated allele version of RcAP2L (RcAP2L172 ) whose presence correlates with double flower formation in Chinese roses and modern roses, such as R. hybrida ‘La France’, that have Chinese rose cultivars as ancestors. Such an allelic form is absent in all simple flower roses. A TE insertion in the 8th intron of RcAP2L leads to the loss of the miR172 target site. We demonstrate that the position of the TE insertion is conserved among different double flower rose varieties that have a parent from the Chinense section. These data indicate that this allele must have been inherited from a single common Chinese ancestor and spread among its double flower modern descendants due to the positive human selection during rose domestication.