“Morphological similarities between R. sects. Synstylae and Chinenses, and R. sects. Rosa and Carolinae are corroborated on the molecular level in our analyses. Four taxa from R. sect. Pimpinellifoliae are further divided into two small clades, which reflect the morphological characters for these species on a molecular level. Whereas three accessions of R. foetida from R. sect. Pimpinellifoliae form a separate clade. R. ×fortuniana forms a clade with R. laevigata based on its maternal inheritance of cpDNA. R. ×cooperii is hypothesized to be a hybrid with seed parent from R. sects. Synstylae and Chinenses. And R. roxburghii should be classified as a section within the R. subgen. Rosa, rather than being treated as its own subgenus, based on molecular analyses.”
These studies are interesting, but I wonder how reliable they are when only one specimen is assumed to represent a species.
Chloroplasts have chromosomes and genes of their own, which would be subject to natural selection.
Also, may Rosa species are allopolyploids derived from two or more diploid ancestors. If crosses between diploids occurred in both directions, the relative suitability of the chloroplast-types would likely favor one type over the other. That is to say, the chloroplast type of an existing polyploid would group that species with the original maternal parent (source of the chloroplast type), ignoring the equal affinity to the other parent(s).
Where studied, chloroplast types can be very diverse within a species.
PLoS One. 2011;6(8):e23980. doi: 10.1371/journal.pone.0023980. Epub 2011 Aug 24.
Chloroplast Genome Variation in Upland and Lowland Switchgrass
Hugh A. Young,Christina L. Lanzatella,Gautam Sarath,Christian M. Tobias
“Few studies have examined variation of the cp genome within a population of a species. However, previous work has genotyped 1575 individuals of Festuca, Lolium, and Festulolium populations and discovered over 500 haplotypes [40]. Further work to sequence the entire Lolium cp genome from mixed genotypes of a single cultivar resulted in the discovery of 10 indels and 40 substitutions within this single cultivar [41]. These data are consistent with our findings of substantial variation within the switchgrass cp genome. As was successful for Lolium haplotypes [40], genotyping cp variation in switchgrass has the potential to resolve relationships between subpopulations. Variation in plastid genomes of switchgrass would not only be useful for this, but also in the expansion of cytoplasmic gene pools in breeding efforts. Plastid type variation has been used for enhancing yield gain as shown in potato [42], and for breeding of bioenergy relevant traits, as recently suggested for Miscanthus [43].”
Chloroplasts can influence a plants tolerance of extreme temperatures. Heat shock proteins, for example, may confer greater tolerance for heat. Differences in chloroplast heat shock proteins have been observed in accessions of Chenopodium album collected in Mississippi and New York.
The types of fatty acids also influence temperature tolerance. Saturated are favored in high temperatures, unsaturated at low.
No doubt there are other differences yet to be discovered.
I think it would be interesting to plot the distribution of the various chloroplast-types against habitat (altitude, temperature during growing season, etc.). It might indicate that the distribution of chloroplast-types among species represents introgression rather than descent from common ancestors.
Too bad HortSci doesn’t allow open access as it publishes a lot of papers relevant to the interests of rose hybridizers.
These studies are interesting, but I wonder how reliable they are when only one specimen is assumed to represent a species.
Disregarding the phylogenetic implications of their data what they do show is that, for the hybridizer, there are some potentially useful genetic similarities to be exploited.
Firstly, if I were in the south I would consider crosses between R. laevigata and fortuniana and its hybrids as a way of capturing the disease resistance of laevigata’s tough rhody like leaves.
Secondly, while I already have hybrids of roxburghii with moderns (one of which, btw, lacks the nasty calyx prickles), knowing that it’s reasonable to expect such crosses to yield fruit by virtue of relatedness is encouraging.
Dr. Walter Lewis has advocated for the unification of Carolinae into Cinnamomeae. That seems to make sense from crossing data too. Rugosa (Cinnmom.)/ blanda (Carol.) hybrids are very fertile as well as some other crosses between the groups.
I agree that some of these molecular studies are only as good as the accuracy of the starting material and how much of a species / section is represented. The material used is often material at botanical gardens that are sometimes misidentified and shared from garden to garden as seed versus clonally propagated plants. With such a wide collection of material at botanical gardens the chance for interspecific hybridization is there. Lots of times folks doing the genetic lab work are great at molecular biology, but may not have the familiarity with the crop and ability/willingness to collaborate with experts to try to use the most reasonable range of confidently identified plants to answer their underlying biological questions. Journals the past decade or so have been more lax at letting molecular work through because it has been a popular approach and may add to readership of their journals and people purchasing pdf versions of articles or more libraries buying subscriptions. Things should continue to tighten I think. For reputable journals things are starting to be more difficult for molecular articles to be accepted to make sure the biological questions they are trying to answer are well thought out.
Some journals like HortScience have options for open access. Authors of HortScience can increase their readership by paying $600 more for immediate open access. Otherwise HortScience is open access after 3 years. They charge members $100 per page plus fees for color figures for standard publication costs. The $600 is above and beyond those fees and many authors don’t want to spend more money if they don’t have to and can invest that money into other projects. The publisher also makes money through library subscriptions. By going totally open access that takes away the need for libraries to buy electronic access for their academic community to have access. More and more libraries are getting away from paper copies. Spreading the financial burden across both authors and libraries/users is the direction ASHS (publisher for HortScience and two other journals) decided to go. Having open access to articles 3 years old or older helps them be accessed by folks and keep their visibility out there. Due to their quality they will hopefully help people be interested in publishing with them and folks asking their library to subscribe.
Lots of times folks doing the genetic lab work are great at molecular biology, but may not have the familiarity with the crop and ability/willingness to collaborate with experts to try to use the most reasonable range of confidently identified plants to answer their underlying biological questions.
Some years ago I worked for a biotech company (IT department). I attended seminars when available, and was amazed/amused at the biochemists or molecular biologists who pontificated about evolution, but were unaware that hybridization was even possible. One speaker looked stunned when I mentioned that hybrids are possible among virtually all species of Rosa. Intergeneric hybrids were beyond him. He held the archaic notion that cross-incompatibility was an inevitable consequence of divergent evolution.
Then there were the two young men who seemed almost giddy talking about cytoplasmic male sterility in maize. Apparently they hadn’t learned about the near-disaster that occurred in the early 1970s when the Southern Corn Blight headed north. It turned out that the Texas Cytoplasm, responsible for the male sterility, also conferred an increased susceptibility to blight. Oops!
If the statement is true, it might relate to differences in organelles. However, he did not use the same Tea parent in the reciprocal crosses. ‘Etoile de Portugal’ had ‘Reine Marie-Henriette’ as pollen parent, but this latter variety was not used as seed-parent in his second group of crosses.
It would be useful to make proper reciprocal crosses to learn whether (and to what extent) heat or cold tolerance is associated with cytoplasmic differences.
Nucleocytoplasmic incompatibility fosters speciation
Donald A. Levin
p. 33
Chloroplast capture
The chloroplast genomes of congeneric species often are well differentiated from one another; and they have been useful in the establishing species’ relationships. However, the phylogenetic trees based on chloroplast markers are not always in accord with trees based on nuclear markers (Wendel and Doyle 1998). In many instances the position of species on chloroplast trees is much closer than their positions on nuclear gene trees. One explanation for this incongruence is chloroplast capture, the replacement of the native chloroplast genome by the genome of another species. Because the position of species on chloroplast trees is often much closer than their positions on nuclear gene trees, it is assumed that chloroplast capture occurred long after the species had diverged from a common ancestor. Put another way, chloroplast introgression had occurred between distantly related species.