Genomic constitution, allopolyploidy, and evolutionary proposal for Cynodon Rich. based on GISH

Evaluation of zinc tolerance and accumulation in eight cultivars of bermudagrass (Cynodon spp.): implications for zinc phytoremediation

Zinc (Zn) is a vital element for plant growth and development, however, excessive Zn is toxic to plants. Common bermudagrass (Cynodon dactylon (L.) Pers.) and hybrid bermudagrass (C. dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) are widely used turfgrass species with strong tolerance to diverse abiotic stresses, including excessive Zn2+ stress. However, the variation of zinc tolerance and accumulation in different bermudagrass cultivars remain unclear. In this study, we systematically analyzed the growth performance, physiological index and ion concentration in eight commercial cultivars of common and hybrid bermudagrass under different concentration of Zn2+ treatments using pot experiments. The results indicated that four cultivars of common bermudagrass could tolerate 20 mM Zn2+, whereas four cultivars of hybrid bermudagrass could only tolerate 10 mM Zn2+. Among the four common bermudagrass cultivars, cultivar Guanzhong and Common showed stronger Zn tolerance and accumulation abilities than other two cultivars. Further analyses of the expression of selected Zn homeostasis-related genes indicated that bermudagrass cultivars with stronger tolerance to excessive Zn have at least one expression-elevated gene involved in Zn homeostasis. These results not only expanded our understanding of Zn tolerance and accumulation in bermudagrass but also facilitated the application of commercial bermudagrass cultivars in phytoremediation of Zn pollution.

Chromosome constitution and genetic relationships of Morus spp. revealed by genomic in situ hybridization

BACKGROUND

Mulberry (Morus spp.) is an economically important woody plant, which has been used for sericulture (silk farming) for thousands of years. The genetic background of mulberry is complex due to polyploidy and frequent hybridization events.

RESULTS

Comparative genomic in situ hybridization (cGISH) and self-GISH were performed to illustrate the chromosome constitution and genetic relationships of 40 mulberry accessions belonging to 12 species and three varietas in the Morus genus and containing eight different ploidy levels. We identified six homozygous cGISH signal patterns and one heterozygous cGISH signal pattern using four genomic DNA probes. Using cGISH and self-GISH data, we defined five mulberry sections (Notabilis, Nigra, Wittiorum, and Cathayana, all contained only one species; and Alba, which contained seven closely related species and three varietas, was further divided into two subsections) and proposed the genetic relationships among them. Differential cGISH signal patterns detected in section Alba allowed us to refine the genetic relationships among the closely related members of this section.

CONCLUSIONS

We propose that GISH is an efficient tool to investigate the chromosome constitution and genetic relationships in mulberry. The results obtained here can be used to guide outbreeding of heterozygous perennial crops like mulberry.

Genetic diversity and population structure of bermudagrass (Cynodon spp.) revealed by genotyping-by-sequencing

Bermudagrass (Cynodon spp.) breeding and cultivar development is hampered by limited information regarding its genetic and phenotypic diversity. To explore diversity in bermudagrass, a total of 206 Cynodon accessions consisting of 193 common bermudagrass (C. dactylon var. dactylon) and 13 African bermudagrass (C. transvaalensis) accessions of worldwide origin were assembled for genetic characterization. Genotyping-by-sequencing (GBS) was employed for genetic marker development. With a minor allele frequency of 0.05 and a minimum call rate of 0.5, a total of 37,496 raw single nucleotide polymorphisms (SNPs) were called de novo and were used in the genetic diversity characterization. Population structure analysis using ADMIXTURE revealed four subpopulations in this germplasm panel, which was consistent with principal component analysis (PCA) and phylogenetic analysis results. The first three principal components explained 15.6%, 10.1%, and 3.8% of the variance in the germplasm panel, respectively. The first subpopulation consisted of C. dactylon accessions from various continents; the second subpopulation was comprised mainly of C. transvaalensis accessions; the third subpopulation contained C. dactylon accessions primarily of African origin; and the fourth subpopulation represented C. dactylon accessions obtained from the Oklahoma State University bermudagrass breeding program. Genetic diversity parameters including Nei's genetic distance, inbreeding coefficient, and Fst statistic revealed substantial genetic variation in the Cynodon accessions, demonstrating the potential of this germplasm panel for further genetic studies and cultivar development in breeding programs.

Genetic Diversity Assessment of Iranian Kentucky Bluegrass Accessions: II. Nuclear DNA Content and Its Association with Morphological and Geographical Features

Poa pratensis L. is a perennial turfgrass with high regeneration and fertility, resistance to cold and drought, and quick colonization. By facultative apomixis, this plant can create a wide range of ploidy levels (2n = 22 to 2n = 154), resulting in a wide range of chromosomal numbers and sexual and apomictic reproductive diversity. The plant materials included fifty accessions from Iran's Center, South, North, North-East, North-West, and West ecoregions. UPOV standards were used to measure the qualities that were researched. The squash technique of chromosome counting revealed that Iranian Kentucky bluegrass accessions had chromosomal counts ranging from 24 to 87. The relative sizes of the 2C genomes were measured using laser flow cytometry. The range of DNA content was fairly wide, ranging from 4.92 to 11.52 pg. DNA content has a strong positive correlation with elevation, a moderately positive correlation with flag leaf length and leaf sheath width, and a negative correlation with inflorescence anthocyanin color and leaf anthocyanin color. The genotypes and ecological zones of this plant in Iran were distinguished based on morphological diversity and DNA content. The results from this study could be useful in identifying and studying wild Kentucky bluegrass genotypes. It aids in predicting the location of rare genotypes used as breeding materials. It can also increase the plant's variability for future generations by introducing new ecotypes, with particular genomic and morphological traits, to previously cultivated populations. We expect that the findings of this study will aid in understanding the evolution of this plant in the context of Iran's climatic variety.

Karyotype Analysis, Genomic and Fluorescence In Situ Hybridization (GISH and FISH) Reveal the Ploidy and Parental Origin of Chromosomes in Paeonia Itoh Hybrids

Itoh hybrids are intersectional hybrids in Paeonia L. with sect. Moutan and sect. Paeonia as paternal and maternal parents, respectively. Therefore, these hybrids have herbaceous stems with improved ornamental value introduced by the paternal parent. Although both of their parents are diploids, Itoh hybrids are triploids. Moreover, the parental origin of their chromosomes has not been extensively studied. This study systematically analyzed the genome size, ploidy, and karyotype of Itoh hybrids and compared them with their parental taxa. Although the monoploid genome size of Itoh hybrids was different, it was not significantly different from that of the parents. However, the size of varieties in the two parental taxa was significantly different from the wild species, probably due to genome rearrangements caused by artificial selection. Further karyotype analysis, correlation analysis, and hierarchical clustering could not identify the parental origin of chromosomes in Itoh hybrids. Verification through genomic and fluorescence in situ hybridization (GISH and FISH) suggested that for the three sets of chromosomes in Itoh hybrids, two were from the paternal parent, and one was from the maternal parent. One of the first two sets was from wild species, and the other from a cultivated variety. GISH could not label the chromosomes of cultivated peonies from the sect. Moutan, probably due to the huge and complex genomes compared with the wild species. Meanwhile, 5S rDNA-based FISH was first applied in Paeonia, which may be used for ploidy assessment. This work may give insights into the utilization of Itoh hybrid resources.

Altitudinal Patterns in Adaptive Evolution of Genome Size and Inter-Genome Hybridization Between Three Elymus Species From the Qinghai–Tibetan Plateau

Genome size variation and hybridization occur frequently within or between plant species under diverse environmental conditions, which enrich species diversification and drive the evolutionary process. Elymus L. is the largest genus in Triticeae with five recognized basic genomes (St, H, P, W, and Y). However, the data on population cytogenetics of Elymus species are sparse, especially whether genome hybridization and chromosomal structure can be affected by altitude are still unknown. In order to explore the relationship between genome sizes, we studied interspecific hybridization and altitude of Elymus species at population genetic and cytological levels. Twenty-seven populations at nine different altitudes (2,800–4,300 m) of three Elymus species, namely, hexaploid E. nutans (StHY, 2n = 6x = 42), tetraploid E. burchan-buddae (StY, 2n = 4x = 28), and E. sibiricus (StH, 2n = 4x = 28), were sampled from the Qinghai–Tibetan Plateau (QTP) to estimate whether intraspecific variation could affect the genomic relationships by genomic in situ hybridization (GISH), and quantify the genome size of Elymus among different altitude ecological groups by flow cytometry. The genome size of E. nutans, E. burchan-buddae, and E. sibiricus varied from 12.38 to 22.33, 8.81 to 18.93, and 11.46 to 20.96 pg/2C with the averages of 19.59, 12.39, and 16.85 pg/2C, respectively. The curve regression analysis revealed a strong correlation between altitude and nuclear DNA content in three Elymus species. In addition, the chromosomes of the St and Y genomes demonstrated higher polymorphism than that of the H genome. Larger genome size variations occurred in the mid-altitude populations (3,900–4,300 m) compared with other-altitude populations, suggesting a notable altitudinal pattern in genome size variation, which shaped genome evolution by altitude. This result supports our former hypothesis that genetic richness center at medium altitude is useful and valuable for species adaptation to highland environmental conditions, germplasm utilization, and conservation.