Cytogenetic Study and Pollen Viability of Phalaenopsis Queen Beer 'Mantefon'

Intergeneric and interspecific hybridization has been employed for the breeding of Phalaenopsis to transfer desirable traits between species, producing novel phenotypes with improved size, color, form, and flower-bearing ability. These characteristics are often enhanced; however, many of these hybrids are triploids and have reduced or complete sterility, for example, Phalaenopsis Queen Beer 'Mantefon', an important novelty-type cultivar in Asia, particularly in China, Japan, and Republic of Korea. Despite the increasing demand for the crop for ornamental purposes, little is known about its cytogenetics, which is essential for breeding and, consequently, crop improvement. In this study, karyotyping using fluorescence in situ hybridization, meiotic chromosome behavior analysis, pollen staining, and in vitro viability germination tests were performed to understand the cause of hybrid sterility and pollen abnormality in Phalaenopsis Queen Beer 'Mantefon' from a cytogenetic perspective. Viability tests revealed pollen infertility at all flower developmental stages, confirmed by the absence of pollen tube growth. Aberrant chromosomal behavior was observed in pollen mother cells (PMCs), frequently forming univalents, chromosomal bridges, and laggards during the entire meiotic process. PMCs were also divided irregularly into sporads with varying numbers of micronuclei, which may be responsible for pollen sterility in this cultivar. Altogether, the cytogenetic analyses provided insights into the pollen development of Phalaenopsis Queen Beer 'Mantefon' and the conceivable causes of its infertility.

Cytogenetics and Consequences of Polyploidization on Different Biotic-Abiotic Stress Tolerance and the Potential Mechanisms Involved

The application of polyploidy in sustainable agriculture has already brought much appreciation among researchers. Polyploidy may occur naturally or can be induced in the laboratory using chemical or gaseous agents and results in complete chromosome nondisjunction. This comprehensive review described the potential of polyploidization on plants, especially its role in crop improvement for enhanced production and host-plant resistance development against pests and diseases. An in-depth investigation on techniques used in the induction of polyploidy, cytogenetic evaluation methods of different ploidy levels, application, and current research trends is also presented. Ongoing research has mainly aimed to bring the recurrence in polyploidy, which is usually detected by flow cytometry, chromosome counting, and cytogenetic techniques such as fluorescent in situ hybridization (FISH) and genomic in situ hybridization (GISH). Polyploidy can bring about positive consequences in the growth and yield attributes of crops, making them more tolerant to abiotic and biotic stresses. However, the unexpected change in chromosome set and lack of knowledge on the mechanism of stress alleviation is hindering the application of polyploidy on a large scale. Moreover, a lack of cost-benefit analysis and knowledge gaps on the socio-economic implication are predominant. Further research on polyploidy coupling with modern genomic technologies will help to bring real-world market prospects in the era of changing climate. This review on polyploidy provides a solid foundation to do next-generation research on crop improvement.

Advances in the Molecular Cytogenetics of Bananas, Family Musaceae

The banana is a staple food crop and represents an important trade commodity for millions of people living in tropical and subtropical countries. The most important edible banana clones originated from natural crosses between diploid Musa balbisiana and various subspecies of M. acuminata. It is worth mentioning that evolution and speciation in the Musaceae family were accompanied by large-scale chromosome structural changes, indicating possible reasons for lower fertility or complete sterility of these vegetatively propagated clones. Chromosomal changes, often accompanied by changes in genome size, are one of the driving forces underlying speciation in plants. They can clarify the genomic constitution of edible bananas and shed light on their origin and on diversification processes in members of the Musaceae family. This article reviews the development of molecular cytogenetic approaches, ranging from classical fluorescence in situ hybridization (FISH) using common cytogenetic markers to oligo painting FISH. We discuss differences in genome size and chromosome number across the Musaceae family in addition to the development of new chromosome-specific cytogenetic probes and their use in genome structure and comparative karyotype analysis. The impact of these methodological advances on our knowledge of Musa genome evolution at the chromosomal level is demonstrated. In addition to citing published results, we include our own new unpublished results and outline future applications of molecular cytogenetics in banana research.

Karyomorphological and SEM studies in newly discovered populations of a critically endangered medicinal plant - Lilium polyphyllum D. Don ex Royle from a high altitude protected area of north-western Himalaya

In this study, new populations of a critically endangered Himalayan herb, Lilium polyphyllum D. Don ex Royle have been reported from Chamba, Himachal Pradesh, India for the first time. Karyotypic, palynological, and spermological studies under the light microscope (LM) and scanning electron microscope (SEM) have been carried out on specimens from these populations with an aim to add more knowledge to the current database of the species. Presently studied individuals depicted a diploid (2x) chromosome count of 2n = 24, which is in confirmation with the previous reports from Kashmir Himalaya. Mitotic study showed a karyotype formula of 2n = 2x = 2m + 2sm + 4st + 16t, that is, 2 metacentric +2 submetacentric +4 acrocentric +16 telocentric chromosomes. LM and SEM observations revealed that the pollen grains are monosulcate, heteropolar, elliptical in polar view, and oblate with reticulate ornamentation. Based on the criteria of number, shape, and arrangement of columellae that form the muri, pollen grains in L. polyphyllum correspond to Martagon type. This is the first SEM based study on pollen grains and seeds of endangered Himalayan white lily. Based on the present ecological data collected we confirm the status of L. polyphyllum to be critically endangered in the study area.

Genetic assessment of the effects of self-fertilization in a Lilium L. hybrids using molecular cytogenetic methods (FISH and ISSR)

Self-fertilization (also termed selfing) is a mode of reproduction that occurs in hermaphrodites and has evolved several times in various plant and animal species. A transition from outbreeding to selfing in hermaphroditic flowers is typically associated with changes in flower morphology and functionality. This study aimed to identify genetic effects of selfing in the F2 progeny of F1 hybrid developed by crossing Lilium lancifolium with the Asiatic Lilium hybrid ‘Dreamland.’ Fluorescence in situ hybridization (FISH) and inter-simple sequence repeats (ISSR) techniques were used to detect genetic variations in plants produced by selfing. The FISH results showed that F1 hybrid were similar to the female parent (L. lancifolium) regarding the 45S loci, but F2 individuals showed variation in the number and location of the respective loci. In F2 progeny, F2-2, F2-3, F2-4, F2-5, and F2-8 hybrids expressed two strong and one weak 5S signal on chromosome 3, whereas F2-7 and F2-9 individuals expressed one strong and two weak signals. Only two strong 5S signals were detected in an F2-1 plant. The ISSR results showed a maximum similarity value of 0.6269 between the female parent and the F2-2 hybrid. Regarding similarity to the male parent, a maximum value of 0.6119 was found in the F2-1 and F2-2 hybrids. The highest genetic distance from L. lancifolium and the Asiatic Lilium hybrid ‘Dreamland’ was observed in the F2-4 progeny (0.6352 and 0.7547, respectively). Phylogenetic relationships showed that the F2 progeny were closer to the male parent than to the female parent. Self-fertilization showed effects on variation among the F2 progeny, and effects on the genome were confirmed using FISH and ISSR analyses.

Patterns of chromosomal variation in Mexican species of Aeschynomene (Fabaceae, Papilionoideae) and their evolutionary and taxonomic implications

A cytogenetic analysis of sixteen taxa of the genus Aeschynomene Linnaeus, 1753, which includes species belonging to both subgenera Aeschynomene (Léonard, 1954) and Ochopodium (Vogel, 1838) J. Léonard, 1954, was performed. All studied species had the same chromosome number (2n = 20) but exhibited karyotype diversity originating in different combinations of metacentric, submetacentric and subtelocentric chromosomes, chromosome size and number of SAT chromosomes. The plasticity of the genomes included the observation in a taxon belonging to the subgenus Aeschynomene of an isolated spherical structure similar in appearance to the extra chromosomal circular DNA observed in other plant genera. By superimposing the karyotypes in a recent phylogenetic tree, a correspondence between morphology, phylogeny and cytogenetic characteristics of the taxa included in the subgenus Aeschynomene is observed. Unlike subgenus Aeschynomene, the species of Ochopodium exhibit notable karyotype heterogeneity. However the limited cytogenetic information recorded prevents us from supporting the proposal of their taxonomic separation and raise it to the genus category. It is shown that karyotype information is useful in the taxonomic delimitation of Aeschynomene and that the diversity in the diploid level preceded the hybridization/polyploidization demonstrated in the genus. The systematic implications of our results and their value can be extended to other Dalbergieae genera as knowledge about the chromosomal structure and its evolution increases.

Cytological variations and long terminal repeat (LTR) retrotransposon diversities among diploids and B-chromosome aneuploids in Lilium amabile Palibin

BACKGROUND

B chromosomes are supernumerary chromosomes found in numerous plant species, including in the genus Lilium. Lilium amabile, an endemic Korean Lilium species, carries B chromosomes which are highly variable in terms of numbers and shape among the accessions collected throughout the Korea. Class 1 retrotransposons are highly abundant in the genome of Lilium species, but their biological functions are still obscure. Lilium species were known to hold high diversities derived from retrotransposons.

OBJECTIVE

In this study, genetic diversities among the L. amabile accessions were analyzed to better understand relationships between genetic variations and cytological diversities.

METHODS

Chromosomes were prepared from 95 L. amabile accessions for cytological identification. Genetic variations were analyzed by inter-retrotransposon amplified polymorphism (IRAP), and genetic differentiation was evaluated via Tajima's D neutrality and F_ST analyses. Population structure and phylogenetic analyses were also carried out.

RESULTS

The L. amabile accessions were classified into 11 cytotypes by the chromosome constitutions. Genetic diversity measured by IRAP analysis revealed high genetic diversity among the accessions. In the joint analysis of cytological variation with genetical variation, IRAP diversity was not related to the cytological diversities of diploid and aneuploids among L. amabile accessions, and genetic differentiation was not obvious. Moreover, the geographical distribution of L. amabile was not related to either IRAP diversity or cytological diversity.

CONCLUSION

The B chromosome-carrying aneuploids occurred randomly among diploids throughout Korea, and IRAP diversification predated L. amabile dispersion in Korea without genetic differentiation.

Characterization of eight species of Aloe (Asphodelaceae) from the nucleolar organizing region

Abstract Nucleolar organizing region of eight species of Aloe was analyzed in somatic metaphases and interphase nuclei. All species showed a uniform 2n=14, with eight large chromosomes and six small chromosomes. Satellites were observed on the long arm of one or two pairs of large chromosomes and/or on the short arm of one of the small pairs. The silver-stained nucleolus organizing regions were located on the subtelomeric region of the long arm of one or two pairs of large chromosomes, except for Aloe dichotoma and Aloe maculata, which the AgNORs were located at a short arm of one of their small chromosomes. In most studied species, the active AgNOR number was four. However, this number changing from one to eight. For all species, the interphase number of nucleoli can be one or two, while, in Aloe excelsa, this number can be changing from one to eight. Polymorphism of active AgNORs and the number of interphase nucleoli were revealed, except for Aloe petricola, which active AgNORs were located only in the subtelomeric regions at the long arm of one of the L2 chromosomes, as well as in the L4 pair, which is agrément with the maximum number (three) of interphase nucleoli.

Análisis del cariotipo del híbrido natural Aloe x spinosissima y de sus parentales Aloe arborescens y Aloe humilis, mediante bandeo cromosómico C, CMA y DAPI

Resumen Se estudia el cariotipo de tres especies de Aloe con bandeo cromosómico C-Giemsa, CMA (Cromomicina A3) y DAPI (4'-6-diamino-2.fenildol), con la finalidad de realizar aportes en su cariomorfometría, ubicación, tamaño de bandas, y discutir evidencias citogenéticas sobre el origen híbrido reportado en A. x spinossisima. Las entidades estudiadas presentan un 2n = 2x = 14 con dos pares de NORs (regiones organizadoras del nucléolo) con satélites asociados y heterocromatina constitutiva CMA + DAPI- (zonas ricas en G-C). La cantidad de heterocromatina, expresada en % de la longitud total del cariotipo (LTC), varía entre las especies: 1,92% en A. arborescens, 1,69% en A. humilis y 1,41% en A. x spinossisima. Se observan bandas en los brazos largos de L2 y L4 de A. arborescens, en L3 y L4 de A. humilis y en A. x spinosissima en el par L4 y en uno de los complementos de L2 y uno de L3. A. x spinossisima presenta valores de la LTC haploide y cantidad de heterocromatina constitutiva, intermedios entre las especies señaladas como progenitoras. Estos resultados y la notoria heteromorfía entre los diferentes pares cromosómicos, refuerzan la hipótesis del origen de A. x spinosissima, como especie híbrida proveniente del cruce natural de A. arborescens x A. humilis.

Study on the homology of the genomes of tetraploid Asiatic lilies (Lilium) using FISH

Asiatic lily cultivars, bred by hybridization and (or) chromosome doubling of species of section Sinomartagon of Lilium, are diploid, triploid, or tetraploid, but the homology of the genomes among species of section Sinomartagon and Asiatic lilies remains unclear. In the present research, two tetraploid Asiatic cultivars were analyzed, using 45S rDNA as probe, for their FISH karyotypes and their chromosomal association, anaphase I, telophase II, and pollen viability were surveyed to assess the multivalent segregation. Chromosomal assortment of six progenies of the two tetraploid cultivars were also investigated. The results showed that the tetraploid cultivars had similar FISH karyotypes, they predominantly formed multivalents, and these were equally separated because their anaphase I, telophase II, and pollen viability were similar to those of diploid species. Apart from minor variations, FISH karyotypes of progenies were similar to each other and to their parents. Based on these results and considering the high crossability among species of section Sinomartagon and (or) Asiatic lilies, we concluded that species of section Sinomartagon and their resulting cultivars share a common genome; thus, polyploidy Asiatic lilies are autopolyploid.

Karyotyping of Brachypodium pinnatum (2n = 18) chromosomes using cross-species BAC-FISH

Identification of individual chromosomes in a complement is usually a difficult task in the case of most plant species, especially for those with small, numerous, and morphologically uniform chromosomes. In this paper, we demonstrate that the landmarks produced by cross-species fluorescence in situ hybridisation (FISH) of Brachypodium distachyon derived bacterial artificial chromosome (BAC) clones can be used for discrimination of Brachypodium pinnatum (2n = 18) chromosomes. Selected sets of clones were hybridised in several sequential experiments performed on exactly the same chromosome spreads, using reprobing of cytological preparations. Analysis of the morphometric features of B. pinnatum chromosomes was performed to establish their total length, the position of centromeres, and the position of BAC-based landmarks in relation to the centromere, thereby enabling their effective karyotyping, which is a prerequisite for more complex study of the grass genome structure and evolution at the cytomolecular level.

Ribosomal DNA distribution and a genus-wide phylogeny reveal patterns of chromosomal evolution in Alstroemeria (Alstroemeriaceae)

PREMISE OF THE STUDY

Understanding the flexibility of monocot genomes requires a phylogenetic framework, which so far is available for few of the ca. 2800 genera. Here we use a molecular tree for the South American genus Alstroemeria to place karyological information, including fluorescent in situ hybridization (FISH) signals, in an explicit evolutionary context.

METHODS

From a phylogeny based on plastid, nuclear, and mitochondrial sequences for most species of Alstroemeria, we selected early-branching (Chilean) and derived (Brazilian) species for which we obtained 18S-25S and 5S rDNA FISH signals; we also analyzed chromosome numbers, 1C-values, and telomere FISH signals (in two species).

KEY RESULTS

Chromosome counts for Alstroemeria cf. rupestris and A. pulchella confirm 2n = 16 as typical of the genus, which now has chromosomes counted for 29 of its 78 species. The rDNA sites are polymorphic both among and within species, and interstitial telomeric sites in Alstroemeria cf. rupestris suggest chromosome fusion.

CONCLUSIONS

In spite of a constant chromosome number, closely related species of Alstroemeria differ drastically in their rDNA, indicating rapid increase, decrease, or translocations of these genes. Previously proposed Brazilian and Chilean karyotype groups are not natural, and the n = 8 chromosomes in Alstroemeria compared to n = 9 in its sister genus Bomarea may result from a Robertsonian fusion.

Distribution of 45S and 5S rDNA sites in 23 species of Eleocharis (Cyperaceae)

Studies of rDNA location in holocentric chromosomes of the Cyperaceae are scarce, but a few reports have indicated the occurrence of multiple 45S rDNA sites at terminal positions, and in the decondensed state of these regions in prometaphase/metaphase. To extend our knowledge of the number 45S and 5S rDNA sites and distribution in holocentric chromosomes of the Cyperaceae, 23 Brazilian species of Eleocharis were studied. FISH showed 45S rDNA signals always located in terminal regions, which varied from two (E. bonariensis with 2n = 20) to ten (E. flavescens with 2n = 10 and E. laeviglumis with 2n = 60). 5S rDNA showed less variation, with 16 species exhibiting two sites and 7 species four sites, preferentially at terminal positions, except for four species (E. subarticulata, E. flavescens, E. sellowiana and E. geniculata) that showed interstitial sites. The results are discussed in order to understand the predominance of terminal rDNA sites, the mechanisms involved in the interstitial positioning of 5S rDNA sites in some species, and the events of amplification and dispersion of 45S rDNA terminal sites.

The Korea brassica genome project: a glimpse of the brassica genome based on comparative genome analysis with Arabidopsis

A complete genome sequence provides unlimited information in the sequenced organism as well as in related taxa. According to the guidance of the Multinational Brassica Genome Project (MBGP), the Korea Brassica Genome Project (KBGP) is sequencing chromosome 1 (cytogenetically oriented chromosome #1) of Brassica rapa. We have selected 48 seed BACs on chromosome 1 using EST genetic markers and FISH analyses. Among them, 30 BAC clones have been sequenced and 18 are on the way. Comparative genome analyses of the EST sequences and sequenced BAC clones from Brassica chromosome 1 revealed their homeologous partner regions on the Arabidopsis genome and a syntenic comparative map between Brassica chromosome 1 and Arabidopsis chromosomes. In silico chromosome walking and clone validation have been successfully applied to extending sequence contigs based on the comparative map and BAC end sequences. In addition, we have defined the (peri)centromeric heterochromatin blocks with centromeric tandem repeats, rDNA and centromeric retrotransposons. In-depth sequence analyses of five homeologous BAC clones and an Arabidopsis chromosomal region reveal overall co-linearity, with 82% sequence similarity. The data indicate that the Brassica genome has undergone triplication and subsequent gene losses after the divergence of Arabidopsis and Brassica. Based on in-depth comparative genome analyses, we propose a comparative genomics approach for conquering the Brassica genome. In 2005 we intend to construct an integrated physical map, including sequence information from 500 BAC clones and integration of fingerprinting data and end sequence data of more than 100,000 BAC clones.