Chromosome Number, Ploidy Level, and Nuclear DNA Content in 23 Species of Echeveria (Crassulaceae)

Abstract

Echeveria is a polyploid genus with a wide diversity of species and morphologies. The number of species registered for Echeveria is approximately 170; many of them are native to Mexico. This genus is of special interest in cytogenetic research because it has a variety of chromosome numbers and ploidy levels. Additionally, there are no studies concerning nuclear DNA content and the extent of endopolyploidy. This work aims to investigate the cytogenetic characteristics of 23 species of Echeveria collected in 9 states of Mexico, analyzing 2n chromosome numbers, ploidy level, nuclear DNA content, and endopolyploidy levels. Chromosome numbers were obtained from root tips. DNA content was obtained from the leaf parenchyma, which was processed according to the two-step protocol with Otto solutions and propidium iodide as fluorochrome, and then analyzed by flow cytometry. From the 23 species of Echeveria analyzed, 16 species lacked previous reports of 2n chromosome numbers. The 2n chromosome numbers found and analyzed in this research for Echeveria species ranged from 24 to 270. The range of 2C nuclear DNA amounts ranged from 1.26 pg in E. catorce to 7.70 pg in E. roseiflora, while the 1C values were 616 Mbp and 753 Mbp, respectively, for the same species. However, differences in the level of endopolyploidy nuclei were found, corresponding to 4 endocycles (8C, 16C, 32C and 64C) in E. olivacea, E. catorce, E. juarezensis and E. perezcalixii. In contrast, E. longiflora presented 3 endocycles (8C, 16C and 32C) and E. roseiflora presented 2 endocycles (8C and 16C). It has been suggested that polyploidization and diploidization processes, together with the presence of endopolyploidy, allowed Echeveria species to adapt and colonize new adverse environments.

Phenotypic Evaluation and Nuclear DNA Content Analysis of Oryzalin-Induced Echeveria Mutant Cultivars

“…Each cycle is performed between the S and G phases. Various Echeveria species displaying endopolyploidy (4C-64C) were reported in a study by Palomino et al (2021); the authors suggested that endopolyploidy plays a vital role in the genus Echeveria as a coping mechanism for these plants in fluctuating environments, which are stressful for plants. However, in 'Sistar', the reduction may be caused by oryzalin as an antimitotic agent, hindering further normal progression of the cycle.…”

The complete chloroplast genome of Echeveria lilacina Kimnach & Moran 1980 (Saxifragales: Crassulaceae)

“…The habitat of E. lilacina ranges from semi-desert areas of west Texas to Argentina, across Mexico, Guatemala, and Central and South America (Palomino et al. 2021 ).…”

Investigations on Nuclear DNA Content and DNA Synthesis in Plants and Fungi Using Flow Cytometry and Fluorescence Microscopy

“…Interestingly, although nuclear DNA content increased with ploidy levels, this increase was not proportional (the monoploid genome size decreased), which confirms genome downsizing during polyploidization of Festuca . Polyploidization also accompanied speciation in the Echeveria genus [ 5 ]. Nuclear DNA content and chromosome number were established for 23 Echeveria species collected in Mexico, revealing the presence of 2 x , 4 x , 5 x , 6 x , and 10 x accessions as well as two hexaploid-aneuploid species; genome size varied from 1.26 pg/2C to 7.70 pg/2C, and monoploid genome size, similarly to Festuca , correlated negatively with ploidy levels.…”

“…Although this is very common in plants, its physiological significance is still unclear and requires further studies. Palomino et al [ 5 ] estimated the endoreduplication pattern in leaves of some species of Echeveria adapted to different environments to show a relationship between endopolyploidy level and stress caused by environmental changes. Depending on the species, the maximum level of endopolyploidy varied between 8C and 64C, and it was suggested that endoreduplication is a defense mechanism triggered by various types of stresses.…”