Genome and karyotype differences between diploid and tetraploid desert roses

Diferenças genômicas e cariotípicas em variedades diploides e tetraploides de rosa-do-deserto

Abstract

Adenium (Apocynaceae) is a genus that contains succulent species, with sculptural stems and large variations in flower shapes and colors. Most of the world’s production chain consists of hybrids, and A. obesum (2n = 22) is the species with the greatest ornamental interest. Adenium arabicum (2n = 44) and A. obesum differ in their morphological characteristics and are found in distinct geographical areas. According to botanical nomenclature rules, A. arabicum should be named A. obesum or a variety thereof. However, this may be genetically questionable. Although genetic variation data for desert roses is scarce, it is crucial for the ornamental plant production sector. The objective of this study was to use data from flow cytometry, karyotype and nucleus characterization, repetitive DNA fraction, bioinformatic tools and physical location of sequences by in situ hybridization to improve understanding of genomic diversity among diploid and tetraploid A. obesum varieties. The karyotypes were composed of meta- and submetacentric chromosomes, and the genome size ranged from 2C = 1.98 pg in diploid samples to 2C = 2.92 pg in tetraploid samples. Chromosome banding revealed similarities between the varieties, with the accumulation of AT-rich regions (DAPI⁺) bands present in the proximal-interstitial chromosome regions, and a smaller number of GC-rich regions (CMA⁺). The DAPI⁺ and CMA⁺ regions, along with ribosomal DNA and Gypsy retrotransposons, predominated in the interphase chromocenters. Differences in the morphology, chromosome number, in situ hybridization signals, and the DNA C-value between these two groups of samples reinforces that they are distinct species and not varieties. Particularly since it would be very difficult to obtain regular meiosis from the crossing of two different sets of chromosomes. Such information is important for the genetic improvement of desert roses.

Keywords:
CMA/DAPI bands; chromocenters; DNA C-value; polyploidy; ribosomal DNA