Tessa Hochhaus (Ph.D. candidate working with roses at Texas A&M) is presenting really valuable information on rose aneuploidy at the conference that is going on this week! She is a talented geneticist and horticulturist that is passionate about a career in teaching.
Here is the link to the abstract https://plan.core-apps.com/pag32/abstract/259e543a-6603-402a-a86c-71ec5b5cc67d
Aneuploidy just means there are incomplete sets of chromosomes (added copy of typically a chromosome or two or at times also a missing chromosome or two). Having an imbalance or unequal dosage of each chromosome can lead to disruptions in gene expression and typically leads to challenges. We find this in the animal world too. Over the decades our relatively few traditional rose geneticists (counting chromosomes under microscopes) have studied the frequency of aneuploid roses (e.g. Dr. Eileen Erlanson). They were pretty rare. Once I found an aneuploid rose among some chemically treated seedlings I had for chromosome doubling. It had 20 vs 21 chromsomes (basic set of chromosomes is 7 and a triploid would have 21 chromosomes, but this rose was missing one). It grew awkwardly and slowly with twisted petioles.
With today’s DNA marker technologies, the team at Texas A&M led by Drs. Riera-Lizarazu and Byrne were able to look at relative dosages of targeted regions of DNA known to be on different chromosomes and then for each rose recognize if everything seemed balanced and there were complete sets of chromosomes, or if not, which chromosome had an extra copy or was missing a copy. Postdoc, Dr. Taniguti especially took the lead in developing computer software to be able to take massive amounts of genetic data and be able to do this. This is especially challenging to do in these polyploid populations of modern roses (for the most part tetraploid) as there are so many sets of chromosomes and genetic information to sift through.
The take home points are that:
-Aneuploids are pretty rare in commercialized roses (about 2%)
-Aneuploids are more common in seedling populations (about 16%)
-Aneuploid seedlings were documented as growing much less vigorously than their siblings with even chromosome sets) explaining why it is so much more less common in the roses that make it to market and why we can get a lot of runts in our seedling populations.
-The extra or missing chromsome(s) tend to be contributed by the female parent much more frequently (87%). I suspect this is likely due to pollen competition. The same rate among the gametes on the female and male side through disrupted meiosis may be occurring, but after pollination the pollen grains with complete sets of chromosomes may be more vigorous and more frequently get to the egg first and participate in fertilization.
-Being able to identify aneuploids is very valuable for genetic studies to better be able to analyze the data. One can either omit the aneuploids or account for them knowing which chromosome or even section of a chromosome has a unique dosage.
Stan Hokanson and I shared genetic marker data from a few of our tetraploid populations we used to map black spot resistance genes and they used that data and kindly included us as coauthors.
I think the greatest utility for us is to appreciate that the runts we often get in our seedling populations have a high chance of being aneuploid due to some disruption during meiosis and sex cell generation. We can anticipate that even with trying to manage better nutrition, etc. most of the small slow growing and awkward seedlings likely won’t/can’t grow out of it and we now have a more likely understanding of what is happening.