Ploidy Series Research Articles

Expression Profiling of MSP1 Gene Involved in Mega-gametophyte Development in Ploidy Series of Guinea Grass (Panicum maximum Jacq.)

Hybrid seeds are playing important role in increasing agricultural production. However, process of hybrid seed development involves high cost for most of the major crops. Under such situation apomixis can play crucial role in creation of one-time hybrid and maintain it for multiple generations. Apomixis and polyploidy are interrelated with each other and expression of apomixis completely relies on polyploidy. Guinea grass (Panicum maximum Jacq.) provides ideal system for research on apomixis and polyploidy because of its extensive diversity in morphological, cytological, biochemical, and molecular characteristics. The experiment was carried out in the eight-ploidy series i.e. 3x, 4x, 5x, 6x, 7x, 8x, 9x, 11x and one obligate sexual Guinea grass genotype SRP75. Considering role of MSP1 gene in apomeiosis, its expression was studied in guinea grass at three developmental stages of spikelet viz., pre-meiotic, meiotic and post-meiotic. Findings of this study highlight the complex regulation of MSP-1 expression during different developmental stages and across various ploidy levels in guinea grass. At pre-meiotic stage, except 4x, downregulation pattern of MSP1 was observed in all the ploidy levels. But opposite was observed in the post-meiotic stage.

Accession-specific parent-of-origin dependent and independent genome dosage effects on salt tolerance in Arabidopsis thaliana.

Improving the salt stress tolerance of crops is an important goal in plant breeding. Changes in the number of chromosome sets (i.e. ploidy level) cause genome dosage effects which can result in enhanced or novel traits. Maternal inheritance versus paternal inheritance of the same chromosome sets can have differential epigenetic effects on traits of F1 offspring. Hence, genome dosage effects can be parent-of-origin independent or dependent. The model plant Arabidopsis thaliana displays both genome dosage and parent-of-origin effects on plant growth under non-stress conditions. Using an isogenic ploidy series of diploid, triploid and tetraploid lines, we investigate the extent of genome dosage effects and their parent-of-origin dependency on in vitro salt stress tolerance of seedlings across 10 different A. thaliana accessions (genetic backgrounds). We detected genome dosage effects on salt stress tolerance for tetraploid lines in five accessions. In addition, through the generation of isogenic reciprocal F1 triploid lines, both parent-of-origin dependent and independent genome dosage effects on salt stress tolerance were detected. Thus, our results indicate not only that genome dosage balance effects can have significant impacts on abiotic stress tolerance in A. thaliana but also that parent-of-origin specific genome dosage effects can affect salt stress tolerance in plants.

Genomic imbalance modulates transposable element expression in maize

Genomic imbalance refers to the more severe phenotypic consequences of changing part of a chromosome compared with the whole genome set. Previous genome imbalance studies in maize have identified prevalent inverse modulation of genes on the unvaried chromosomes (trans) with both the addition or subtraction of chromosome arms. Transposable elements (TEs) comprise a substantial fraction of the genome, and their reaction to genomic imbalance is therefore of interest. Here, we analyzed TE expression using RNA-seq data of aneuploidy and ploidy series and found that most aneuploidies showed an inverse modulation of TEs, but reductions in monosomy and increases in disomy and trisomy were also common. By contrast, the ploidy series showed little TE modulation. The modulation of TEs and genes in the same experimental group were compared, and TEs showed greater modulation than genes, especially in disomy. Class I and II TEs were differentially modulated in most aneuploidies, and some superfamilies in each TE class also showed differential modulation. Finally, the significantly upregulated TEs in three disomies (TB-7Lb, TB9Lc, and TB-10L19) did not increase the proportion of adjacent gene expression when compared with non-differentially expressed TEs, indicating that modulations of TEs do not compound the effect on genes. These results suggest that the prevalent inverse TE modulation in aneuploidy results from stoichiometric upset of the regulatory machinery used by TEs, similar to the response of core genes to genomic imbalance.

Genome size, ploidy levels, and development of novel SSR primer to evaluate genetic diversity of Corylopsis Siebold & Zucc. germplasm collections

Corylopsis Seibold & Zucc. is a genus of flowering shrubs with few cultivars and little information on genome size, ploidy levels, and genetic relationships among taxa. The United States National Arboretum and collaborating gardens in North America maintain a diverse germplasm collection of Corylopsis including cultivated and wild-collected taxa. The objectives of this study were to determine genome size, ploidy, and genetic diversity in Corylopsis. Flow cytometry revealed a ploidy series of diploid, tetraploid, pentaploid, and hexaploid taxa in Corylopsis with 2C genome sizes ranging from 1.9 pg to 5.7 pg. Representative taxa were selected for root tip cytology, revealing diploid (C. platypetala Rehder & E.H. Wilson), tetraploid (C. gotoana Makino), pentaploid (unnamed hybrid selection), and hexaploid (C. willmottiae Rehder & E.H. Wilson) taxa. Seventeen genomic simple sequence repeat markers were developed and used to determine the genetic diversity of Corylopsis. These markers had an average of 7.4 alleles per locus with a range of three to 17 alleles. A dendrogram was generated by unweighted pair group method with arithmetic mean (UPGMA) cluster analysis using the Jaccard similarity coefficient to visualize genetic relationships and ploidy series within taxa. Information gained from this study will further breeding efforts and aid management of germplasm collections of Corylopsis.

Genome Sizes, Ploidy Levels, and Base Compositions of Styrax Species and Cultivars

Styrax L. is a genus of ≈130 species, many with horticultural traits of interest, though sparsely represented in cultivation. Previous studies reporting chromosome counts have established a base chromosome number of x = 8 and provided evidence of diploid, tetraploid, pentaploid, and hexaploid levels within the genus, including the more commonly cultivated Styrax japonicus Siebold & Zucc. being reported as pentaploid. Little has been reported relative to genome size within the Styracaceae. We conducted flow cytometry using fluorochromes propidium iodide (PI) and 4′,6-diamidino-2-phenylindole (DAPI) to estimate relative 2C genome size and ploidy of 47 accessions representing 15 species of Styrax and base composition of a subset of 9 accessions representing 6 species. Cytologic analysis of chromosomes was completed on Styrax confusus Hemsl. for ploidy calibration to genome size. Diploids, tetraploids, pentaploids, hexaploids, and octoploids were identified. Relative 2C genome size ranged from 1.38 to 6.61 pg. This survey confirms published ploidy for Styrax americanus Lam., Styrax obassia Siebold & Zucc., Styrax redivivus (Torr.) L.C.Wheeler (diploid), and S. japonicus (pentaploid); suggests alternate ploidy levels and/or ploidy series for Styrax grandifolius Aiton (diploid) and Styrax hookeri C.B.Clarke (octoploid); and establishes ploidy levels for Styrax glabrescens Benth., Styrax odoratissimus Champ. ex Benth., Styrax officinalis L., Styrax platanifolius Engelm. ex Torr., Styrax ramirezii Greenm., Styrax wilsonii Rehder (diploid), Styrax confusus, Styrax hemsleyanus Diels (tetraploid), and Styrax fortunei Hance (diploid and hexaploid).

Gene Expression and Physiological Differences in Neo-Octoploid Switchgrass Subjected to Drought Stress

Switchgrass (Panicum virgatum L.) has been subject to breeding to improve its yield and composition for bioenergy. Increased tolerance of environmental stress is another factor that can improve yields over the life span of a field plot. Natural ploidy series act as somewhat distinct gene pools in switchgrass that maintain differences with respect to tolerance of environmental stress and which can only be bridged through whole genome reduction or duplication events. In order to document potential wide-ranging effects of whole genome duplication, we examined the effects of water stress on growth, physiology, and gene expression in individual tetraploid clones of the switchgrass cultivar “Liberty” as well as neo-octoploid lines derived from it. The neo-octoploids behaved similarly to Liberty under water stress and recovery conditions: Water-stressed plants had approximately 50% or greater reduction of biomass, plant height, and node numbers. Tiller number and photosynthesis rates of stressed plants were reduced by up to 50%, while proline levels were significantly higher in stressed plants than well-watered plants. A total of 6134 differentially expressed genes (8% of the annotated genes with detectable expression in crown tissue) were detected under water-deficit stress, while 3310 differentially expressed genes were detected in crown tissue after 1 week of recovery from water-deficit stress relative to well-watered treatments. Only 187 genes were identified as being differentially expressed between 4x Liberty and its 8x derivatives. This study indicates neo-octoploids could be viable 8x-equivalent Liberty stand-ins for future breeding assays.

Cytogenetics, Ploidy, and Genome Sizes of Camellia and Related Genera

Camellia L., the most speciose member of the diverse tea family Theaceae, has a long and complex horticultural history. Extensive cultivation and hybridization have produced thousands of varieties of Camellia, including commercially important crops such as cultivated tea, oilseed, and iconic flowering shrubs. Cytogenetics of Camellia and related genera is complicated; chromosome number and ploidy can vary widely between species, and interspecific and interploid hybridization occurs. However, specific information regarding cytogenetics of many species, cultivars, and modern hybrids is lacking. The objectives of this study were to compile a consolidated literature review of the cytogenetics of Camellia and related genera and to determine chromosome numbers, ploidy, and genome sizes of specific accessions of selected species, cultivars, and interspecific and interploid hybrids. A review of the existing literature regarding Theaceae cytogenetics is presented as a consolidated reference comprising 362 taxa. Genome sizes were determined with flow cytometry using propidium iodide as a fluorochrome and Pisum sativum ‘Ctirad' and Magnolia virginiana ‘Jim Wilson’ as internal standards. Chromosome numbers of selected taxa were determined using traditional cytology and were used to calibrate genome sizes with ploidy level. Our results confirmed a base chromosome number of x = 15 for Theeae including Camellia, x = 17 for Stewartiae, and x = 18 for Gordoniae. Surveyed camellias ranged from 2n = 2x = 30 to 2n = 8x = 120, including diploids, triploids, tetraploids, pentaploids, hexaploids, and octoploids. Previously uncharacterized taxa such as Camellia azalea, C. amplexicaulis, C. chrysanthoides, C. cordifolia, C. cucphuongensis, C. flava, C. nanyongensis, and C. trichoclada were found to be diploid. Ploidy was also newly determined for Schima argentea, S. khasiana, S. remotiserrata, and S. sinensis (all diploids). Both diploid and triploid Stewartia ovata were found, and a ploidy series was discovered for Polyspora that ranged from diploid to octoploid. Ploidy determinations were used to confirm or challenge the validity of putative interploid hybrids. Monoploid genome sizes varied among subfamily and genera, with 1Cx values ranging from 0.80 pg for Franklinia to a mean of 3.13 pg for Camellia, demonstrating differential rates of genome expansion independent of ploidy. Within Camellia, monoploid genome sizes varied among subgenera, sections, and some species (range, 2.70–3.55 pg). This study provides a consolidated and expanded knowledgebase of ploidy, genome sizes, hybridity, and reproductive pathways for specific accessions of Camellia and related genera that will enhance opportunities and strategies for future breeding and improvement within Theaceae.

Variation in Genome Size, Ploidy, Stomata, and rDNA Signals in Althea

Althea (Hibiscus syriacus) is a shrub prized for its winterhardiness and colorful summer flowers. Altheas are tetraploids (2n = 4x = 80); however, breeders have developed hexaploids and octoploids. Previous studies report anatomical variation among polyploids, including stomata size. The purpose of this study was 4-fold. First, identify genome size and ploidy variation in cultivars via flow cytometry and chromosome counts. Second, create a ploidy series consisting of 4x, 5x, 6x, and 8x cytotypes. Third, investigate the ploidy series for variation in stomatal guard cell lengths, stomatal density, and copy number of fluorescent ribosomal DNA (rDNA) signals. Fourth, investigate segregation patterns of rDNA signals in a subset of pentaploid seedlings. Flow cytometry revealed most cultivars to be tetraploid with holoploid 2C genome sizes from 4.55 ± 0.02 to 4.78 ± 0.06 pg. Five taxa (‘Aphrodite’, ‘Pink Giant’, ‘Minerva’, Azurri Satin®, and Raspberry Smoothie™) were hexaploids (6.68 ± 0.13 to 7.05 ± 0.18 pg). Peppermint Smoothie™ was a cytochimera with tetraploid cells (4.61 ± 0.06 pg) and octoploid cells (8.98 ± 0.13 pg). To create pentaploids, reciprocal combinations were made between hexaploid ‘Pink Giant’ and tetraploid cultivars. To create octoploids, seedlings were treated with agar solutions containing 0.2% colchicine or 125 μM oryzalin. Guard cell lengths were significantly different among the four cytotypes: 4x (27.36 ± 0.04 μm), 5x (30.35 ± 1.28 μm), 6x (35.59 ± 0.63 μm), and 8x (40.48 ± 1.05 μm). Measurements of stomatal density revealed a precipitous decline in average density from the 4x cytotype (398.22 ± 15.43 stomata/mm2) to 5x cytotype (194.06 ± 38.69 stomata/mm2) but no significant difference among 5x, 6x, and 8x cytotypes. Fluorescent in situ hybridization (FISH) revealed an increase in 5S and 45S rDNA signals that scaled with ploidy: 4x (two 5S + four 45S), 6x (three 5S + six 45S), and 8x (four 5S + eight 45S). However, pentaploid (5x) seedlings exhibited random segregation of rDNA signals between the 4x and 6x cytotypes, including all six possible combinations (two 5S, three 5S) × (four 45S, five 45S, six 45S).

MЕКСИКАНСКИЙ ВИД КАРТОФЕЛЯ SOLANUM NEOANTIPOVICZII BUK. (= S. STOLONIFERUM SCHLECHTD.) ИЗ ТАКСОНОМИЧЕСКОЙ СЕРИИ LONGIPEDICELLATA BUK. ДЛЯ ИСПОЛЬЗОВАНИЯ В МЕЖВИДОВОЙ ГИБРИДИЗАЦИИ

Background . There are more than 200 tuber-bearing species in the genus Solanum L. Many of them possess valuable traits able to improve some characteristics in present-day potato cultivars. Wild potato species have formed an entire ploidy series ranging from diploid to hexaploid. Many wild species have not yet been used in potato breeding. A barrier exists in crosses due to differences in chromosome numbers and EBN of parental species. In our previous evaluation of the accession S. neoantipoviczii Buk. VIR k-8505 was found to be highly resistant to Phytophthora infestans and to tree strains of Potato Virus Y (PVY) conferring resistance through the gene Rysto. In J. Hawkes's monography this species is mentioned as synonymous to S. stoloniferum Schlechtd. Russian taxonomist S. M. Bukasov recognized it as an independent species. At the same time D. Correll hypothesized that this species is the hybrid between tetraploid S. stoloniferum and diploid S. verrucosum Schlechtd. We counted the chromosome number in thirty seedlings of the accession S. neoantipoviczii k-8505 and studied the crossability of this accession in combinations with several other species. Material and methods. The plants of the species: S. neoantipoviczii Buk (female parent), original hybrid S. microdontum Bitt. x S. tarijense Hawk., S. berthaultii Hawk., S. ruiz-ceballosii Card., S. kurtzianum Bitt. et Wittm., S. papita Rydb., S. phureja Juz. et Buk. and S. tuberosum L. (male parents) differing in chromosome numbers and previously studied for useful traits were included in hybridization. The chromosome counting was performed in meristem root cells, extracted from in vitro plants. Hybridization was performed using cut branches of female parents after bud decapitation. Results and conclusions . Plants of the accession S. neoantipoviczii k-8505 were basically found tetraploid. In the crosses of S. neoantipoviczii used as the female parent, seeds were obtained in combinations with the accessions of wild (S. berthaultii, S. kurtzianum, S. papita, S. ruiz-ceballosii, hybrid S. microdontum x S. tarijense) and cultivated (S. phureja, S. tuberosum) potato species. Low seed numbers were recorded in the crosses with S. kurtzianum and S. berthaultii. In crosses with the other species, the seed number varied from 50.4 to 106.6.

Global impacts of chromosomal imbalance on gene expression in Arabidopsis and other taxa

Changes in dosage of part of the genome (aneuploidy) have long been known to produce much more severe phenotypic consequences than changes in the number of whole genomes (ploidy). To examine the basis of these differences, global gene expression in mature leaf tissue for all five trisomies and in diploids, triploids, and tetraploids of Arabidopsis thaliana was studied. The trisomies displayed a greater spread of expression modulation than the ploidy series. In general, expression of genes on the varied chromosome ranged from compensation to dosage effect, whereas genes from the remainder of the genome ranged from no effect to reduced expression approaching the inverse level of chromosomal imbalance (2/3). Genome-wide DNA methylation was examined in each genotype and found to shift most prominently with trisomy 4 but otherwise exhibited little change, indicating that genetic imbalance is generally mechanistically unrelated to DNA methylation. Independent analysis of gene functional classes demonstrated that ribosomal, proteasomal, and gene body methylated genes were less modulated compared with all classes of genes, whereas transcription factors, signal transduction components, and organelle-targeted protein genes were more tightly inversely affected. Comparing transcription factors and their targets in the trisomies and in expression networks revealed considerable discordance, illustrating that altered regulatory stoichiometry is a major contributor to genetic imbalance. Reanalysis of published data on gene expression in disomic yeast and trisomic mouse cells detected similar stoichiometric effects across broad phylogenetic taxa, and indicated that these effects reflect normal gene regulatory processes.

Ploidy dependent expression of apomixis and its components in guinea grass (Panicum maximum Jacq.)

Panicum maximum (guinea grass) is a model crop for apomixis and polyploidy studies. It is predominantly tetraploid (2n = 32) and is characterized by gametophytic apomixis, Panicum-type apospory and pseudogamous endosperm development. The three components of apomixis, viz. apomeiosis, parthenogenesis and functional endosperm development, can be uncoupled in this crop. An exhaustive single progenitor-derived ploidy series comprising of 32 accessions representing 3x, 4x, 5x, 6x, 7x, 8x, 9x and 11x cytotypes was utilized in present study to understand ploidy effects on expression of apospory as well on uncoupled components in two phases of progeny formation i.e. in matured ovules (using embryo-sac analysis) and in matured self-pollinated seeds (using Flow Cytometric Seed Screen method). Rise in ploidy enhanced the formation of sexual embryo-sacs (ES) thereby increasing the frequency of facultative accessions at higher ploidy level. Our results suggested that the eventual phenotype depends on relative doses of apospory and sexual factors in the genome. Ploidy level was also found affecting the penetrance and expressivity of uncoupled apomixis components. Formation of BIII hybrids (3n) appeared to be more stabilised and less affected by the ploidy change, however, formation of M1 (1n) progenies increased with the rise in ploidy. Ploidy effects on traits such as occurrence of multiple ES, autonomous endosperm development, and twin embryos were also studied. Flexibility of guinea grass to tolerate excessive genome burden and successful formation of seeds overcoming endosperm balance number and endosperm imprinting constraints is also discussed.

Variation in nuclear DNA content and chromosome numbers in blueberry

Abstract Commercial blueberry production in the U.S. relies on cultivars derived from combinations of different blueberry species. Interspecific hybridization continues to be a vital strategy for blueberry breeding, especially in regards to improving abiotic and biotic stress tolerance to expand the range of production. Blueberry species have many different genome sizes, presumably due to differing ploidy levels and/or DNA content. In some species, such as Vaccinium corymbosum L. and V. pallidum Aiton, there are also different ploidy series available for breeding, further complicating the observed DNA content in elite selections. In this study we determined DNA content in 77 blueberry taxa including 11 species and 64 hybrid cultivars. Among these taxa are 11 diploid, 49 tetraploid, one pentaploid, and 16 hexaploid plants representing southern highbush, northern highbush, low bush, rabitteye, and half high blueberries. DNA content was measured for three separate tissue samples from at least three individual plants per taxa for accuracy. Absolute genome sizes varied significantly (P = 0.05) among ploidy levels, with 2C-value means of 1.09 pg for diploid, 2.10 pg for tetraploid, and 3.60 pg for hexaploid taxa. Holoploid genome size (2C DNA) was significantly correlated with ploidy or presumed chromosome number (2n) (r = 0.96, P = 0.0001) but only weakly correlated with monoploid genome size (1Cx-DNA) (r = 0.43, P = 0.0001).

Epigenetic contribution to successful polyploidizations: variation in global cytosine methylation along an extensive ploidy series in Dianthus broteri (Caryophyllaceae).

Polyploidization is a significant evolutionary force in plants which involves major genomic and genetic changes, frequently regulated by epigenetic factors. We explored whether natural polyploidization in Dianthus broteri complex resulted in substantial changes in global DNA cytosine methylation associated to ploidy. Global cytosine methylation was estimated by high-performance liquid chromatography (HPLC) in 12 monocytotypic populations with different ploidies (2×, 4×, 6×, 12×) broadly distributed within D.broteri distribution range. The effects of ploidy level and local variation on methylation were assessed by generalized linear mixed models (GLMMs). Dianthus broteri exhibited a higher methylation percent (˜33%) than expected by its monoploid genome size and a large variation among study populations (range: 29.3-35.3%). Global methylation tended to increase with ploidy but did not significantly differ across levels due to increased variation within the highest-order polyploidy categories. Methylation varied more among hexaploid and dodecaploid populations, despite such cytotypes showing more restricted geographic location and increased genetic relatedness than diploids and tetraploids. In this study, we demonstrate the usefulness of an HPLC method in providing precise and genome reference-free global measure of DNA cytosine methylation, suitable to advance current knowledge of the roles of this epigenetic mechanism in polyploidization processes.

Mating type and ploidy effect on the β-glucosidase activity and ethanol-producing performance of Saccharomyces cerevisiae with multiple δ-integrated bgl1 gene

In order to investigate the effect of mating type and ploidy on enzymatic activity and fermentation performance in yeast with multiple δ-integrated foreign genes, eight ploidy series strains were constructed. The initial haploid strain BGL-a was shown to contain about 19 copies of the bgl1 gene. In rich media containing 2% (w/v) sugar the specific activities of BGL-aα were lower than those of BGL-aa or BGL-αα, which indicates the existence of mating type effects. While the maximum OD660 decreased with rising ploidy, the biomass yield showed no significant difference between the eight strains and the specific activities (expressed as U/mL or U/mg DCW) showed little to no variation. When cellobiose was used as the carbon source and β-glucosidase substrate, β-glucosidase was expressed more quickly and at higher levels than in glucose-containing media. The maximum specific activitiy values obtained were 19.07U/mL and 19.39U/mL for BGL-αα and BGL-aa, repsectively. The anaerobic biomass and ethanol-producing performance in rich media containing 10% cellobiose showed no significant difference among the eight strains. Their maximal ethanol concentrations and corresponding yields ranged from 40.27 to 43.46g/L and 77.56 to 83.71%, respectively. When the acid- and alkali-pretreated corncob (10% solids content) was used, the diploid BGL-aα fermented the best. When urea was used as the only supplemented nutrient, the ethanol titer and yield were 35.65g/L and 83.69%, respectively, while a control experiment using industrial Angel yeast with exogenous β-glucosidase addition gave values of 37.93g/L and 89.04%. The combined effects of δ-integration of bgl1, ploidy and mating type result in BGL-aa or BGL-αα being the optimal choice for enzyme production and BGL-aα being more suitable for cellulosic ethanol fermentation. These results provide valuable information for future yeast breeding and utilization efforts.

Analyses of phenotype and ARGOS and ASY1 expression in a ploidy Chinese cabbage series derived from one haploid.

The aim of this research was to improve our understanding of how ploidy level influences phenotype and gene expression in Chinese cabbage (Brassica rapa L. ssp. pekinensis). Haploid plants (2n = 10) was induced by 0.2% colchicine to produce diploid (2n = 20) and tetraploid plants (2n = 40). The aneuploid (2n = 24) was also obtained by hybridization between diploid plants as the female and tetraploid plants. The ploidy levels of all plants were identified through chromosome counts and flow cytometry. Leaves and petals became larger as the ploidy level increased from haploid to diploid, and from aneuploid to tetraploid. Similarly, expression of ARGOS was regulated by genome size, increasing in parallel with the level of ploidy. Among the four ploidy types, expression was stronger in the floral buds than in the leaves. Expression by ASY1 also differed according to ploidy level, being highest in diploid plants, followed in order by tetraploids. Expression was similar between haploids and aneuploids at two stages—prior to and after meiosis—but was higher in the haploids during meiosis. When buds were compared within the same ploidy type at different stages, ASY1 expression was obviously higher during meiosis than either before or after. Our study demonstrated the generation and phenotype of a ploidy Chinese cabbage series derived from one haploid. Expression of genes ARGOS and ASY1 were modulated by genome size in this ploidy series, and the regulated patterns of the two genes was different.

Genome Sizes and Ploidy Levels in the Genus Kalmia

Kalmia is a highly ornamental genus of shrubs native to North America and Cuba and grown as a valuable nursery crop throughout much of the temperate world. Although most species of Kalmia have previously been found to be diploid with 2n = 2x = 24, one species, Kalmia polifolia, has been found to be tetraploid. However, sampling within the genus has been limited, and information on the ploidy levels of specific cultivars is lacking. The objective of this study was to determine the relative genome sizes and ploidy levels of species, hybrids, and cultivars of Kalmia. Flow cytometry was used to determine the relative genome sizes of 67 accessions representing species, interspecific hybrids, cultivars, and chemically induced polyploids. Traditional cytology was used to calibrate genome sizes with ploidy levels. Results showed that relative genome sizes were conserved with 1Cx values ranging from 0.57 pg for Kalmia carolina to 0.70 pg for Kalmia latifolia. Most species of Kalmia were diploid including K. buxifolia (Leiophyllum buxifolium), K. carolina, K. cuneata, K. hirsuta, K. latifolia, and K. microphylla. Although plants of K. carolina (Kalmia angustifolia var. carolina) were uniformly diploid, the closely related, but more northerly distributed, K. angustifolia was primarily tetraploid, providing additional justification for treating these as separate species. An unusual triploid of K. angustifolia f. candida was also documented. Kalmia polifolia included both tetraploid and potentially pentaploid individuals, indicating a ploidy series within this species. Kalmia latifolia cultivars also included one triploid, two cytochimeras, and two chemically induced tetraploids. Overall, polyploidy was more prevalent in Kalmia than previously reported and varied both within and among species. This broader survey of relative genome sizes and ploidy levels in Kalmia provides valuable information for plant breeders and new insights into the systematics and cytogenetics of the genus.

Phylogenetic relationships in the extreme polyploid complex of the New Zealand genus Leptinella (Compositae: Anthemideae) based on AFLP data

AbstractAFLP fingerprinting for 236 individuals from 75 populations and 31 taxa of the Southern Hemisphere genus Leptinella (Compositae: Anthemideae) was carried out in order to infer the evolutionary relationships among the New Zealand representatives of the genus and to compare the results with sequence–based phylogenetic reconstructions for the genus. The New Zealand–based clade of the genus is characterised by the formation of an impressive polyploid complex with ploidy levels reaching from 4x to 24x. We observe a tripartition of taxa into species groups that correspond to species assemblages also found in the sequence–based reconstructions: A basal, presumably paraphyletic stock of tetraploid species (AFLP cluster A) corresponding to the morphologically defined Leptinella subg. Radiata is connected through one of its sub–clusters (A1, the L. minor group) with a monophyletic group of two clusters (B and C) with a sister–group relationship. While AFLP cluster B remained on the tetraploid level, clusters A and C form ploidy series reaching the levels of 16x and 24x, respectively. The lack of intermediate AFLP genotypes demonstrates that polyploidisation has occurred independently in the two clusters forming the L. pectinata/L. pyrethrifolia assemblage (cluster A2) in L. subg. Radiata and the L. dioica assemblage (clusters C1 and C2) in L. subg. Leptinella. The joint consideration of sequence–based reconstructions and AFLP fingerprint patterns further allows the formulation of an evolutionary hypothesis for the genus that tries to explain differentiation processes in a temporal and geographic framework: The available data argue for a Late Miocene (ca. 5–10 Ma) establishment of Leptinella in New Zealand and its further differentiation on the tetraploid level throughout the Pliocene and the Early Pleistocene, followed by extensive polyploidisation cycles caused by the climatic oscillations of the Pleistocene.

Genetic response of Paspalum plicatulum to genome duplication.

Paspalum plicatulum is a perennial rhizomatous grass with natural diploid and polyploid cytotypes. In this study, we investigated the occurrence of sequence polymorphisms arising immediately after genome autoduplication in this species. Two mixoploid plants (4C and 7D) were previously obtained through colchicine treatment of seeds generated by open pollination of a diploid plant (H14-2x). Diploid and tetraploid sectors from both mixoploids were dissected to generate two ploidy series (4C-2x/4C-4x and 7D-2x/7D-4x). Molecular fingerprints were generated from the maternal plant H14-2x, both ploidy series (4C-2x/4C-4x and 7D-2x/7D-4x), and a tetraploid plant (C1) produced by selfing 7D-4x. Our results indicate that immediately after polyploidization P. plicatulum suffers genetic rearrangements affecting ~28-38 % of the genome. Band gain and loss were equally prevalent at a statistically significant level. At least 5.62 % of the genome experimented recurrent genetic variation in a non-random basis with a confidence of 94.88 %. A significant proportion of novel bands (36 out of 195; 18.4 %) was detected in the C1 tetraploid plant. Half of these bands were not amplified in either H14-2x or 7D-4x, while the remainders were present in H14-2x but absent in 7D-4x. Our results indicate the occurrence of a considerable number of genetic changes in P. plicatulum immediately after polyploidization, some of which were recurrently detected in different independent events. Moreover, we confirmed that after polyploidization, lost ancestral alleles were spontaneously recovered in further generations, a phenomenon previously reported by other research groups.

Genome size variation in guayule and mariola: Fundamental descriptors for polyploid plant taxa

Guayule (Parthenium argentatum A. Gray) has tremendous potential as a domestic source of natural rubber production in the southwestern United States. However, genetic improvement of guayule has been slowed by its complex mode of reproduction, natural ploidy series, and lack of genetic and genomic resources. The interspecific hybridization of guayule with its closest sister taxon mariola (P. incanum Kunth) offers an opportunity to access novel genetic variation for guayule breeding programs, but mariola accessions available from the U.S. National Plant Germplasm System (NPGS) have never been evaluated for natural variation in ploidy level. In addition, the nuclear genome sizes for guayule and mariola at any ploidy level are unknown. To that end, we examined the ploidy of 10 mariola accessions, which revealed a natural polyploid series ranging from triploid (2n=3x=54) to pentaploid (2n=5x=90). In contrast, a ploidy analysis of five guayule accessions uncovered a natural polyploid series that ranged from diploid (2n=2x=36) to hexaploid (2n=6x=108). More than one ploidy level among individual plants (mixed ploidy) and instances of aneuploid plants were observed for accessions of both guayule and mariola. The nuclear genome sizes of guayule and mariola were similar at identical ploidy levels, and the genome size of diploid guayule (1624Mb) was almost twofold smaller than the genomes of sunflower (H. annuus L. 2n=2x=34) and lettuce (L. sativa L.; 2n=2x=18), two other Compositae (Asteraceae) species that are being genome-sequenced. The results from this study will serve as a foundation for interspecific breeding and genome sequencing of guayule and mariola.

Construction of ploidy series of Saccharomyces cerevisiae by the plasmid YCplac33-GHK

An effective approach, using the plasmid YCplac33-GHK, is developed to construct a ploidy series of Saccharomyces cerevisiae. YCplac33-GHK harbors the HO gene under the control of galactose-inducible promoter and KanMX4 as the selective marker. The simple method can solve the problem of industrial applications of strains with resistance genes.