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Epigenetic regulatory DNA methylation and post-translational histone modifications are considered to be highly conserved. Recent findings however suggest that chromosomal distribution of individual modifications (acetylation, methylation, phosphorylation) can differ within and between the groups of eukaryotes, indicating the obvious possibility of evolutionary divergence in reading the ‘histone code’. Orchids are known for their complex genome organization and evolution. Current trends of formation of artificial and natural polyploid orchids generally provide superior genetic variability, size, substance and form of flowers to their diploid counterparts. Here, we report the comparative chromosomal distribution of 5mC and twelve selected modified histones (methylated, acetylated and phosphorylated) between diploid and autotetraploid Dendrobium nobile at critical cytogenetic landmarks (interphase, metaphase and anaphase) of mitotic cell division to understand the underlying consequences of polyploidization on the holistic chromatin environment in higher angiosperms like orchids. Comparative in situ immuno-detection of 5-mC sites revealed increment of DNA methylation in autopolyploid D. nobile in comparison to its diploid prototype. Notably, only H3K9me1 and H3K27me2 revealed its conserved chromosomal distribution between diploid and autotetraploid D. nobile by labeling the heterochromatin and euchromatin respectively. Whereas, other epigenetic methylated and acetylated histone marks showed more or less altered/facultative distribution pattern. Histone phosphorylation did not show any alteration in chromosomal distribution between diploid and autopolyploid D. nobile. It has been concluded that polyploidization events may influence/altered the chromosomal distribution of methylated and acetylated histone marks in higher plants. This study might serve as a baseline data to understand the affect of polyploidization on epigenetic alteration associated with DNA and histone modification that ultimately play a crucial role in speciation and genome evolution of higher angiosperms like orchids.

Doubled haploid (DH) breeding eventually offers unique advantages for rapid genetic improvement of wheat in a single generation by achieving absolute homozygosity and enhanced selection efficiency. A new perennial invasive weed i.e., Imperata cylindrica has already proved its importance in haploid wheat induction through Imperata-mediated chromosome elimination process. Whereas, cytological evidences and the actual mechanism of haploid induction through chromosome elimination in wheat x I. cylindrica hybrids are well known, but which genome(s) of wheat (AA/BB/DD) are actually involved in such haploid formation has remained elusive. Therefore, in order to identify the genome-specific triggering of Imperata-mediated chromosome elimination in development of wheat haploids, 11 wheat genotypes including Ae. tauschii and D-genome chromosome substitution lines of the durum wheat variety ‘Langdon’ were crossed with I. cylindrica and examined with the prime aim of producing haploids of Ae. tauschii. The crosses suggest that only bread wheat, Ae. tauschii and Triticale (containing D genome) were successful to develop haploid plants through chromosome elimination process. Higher frequencies of embryo formation were obtained primarily in substitution lines with chromosomes 7D. The detailed anatomical and cytological analyses suggest that : (i) genome/genotypic specificity plays a key role in haploid induction through Imperata-mediated chromosome elimination process, (ii) D-genome triggers the chromosome elimination and haploid production in wheat x Imperata, (iii) some D-genome chromosomes (primarily 7D) substituted lines in wheat genetic background may enhance crossability with Imperata in the formation of haploid wheat. To the best of our knowledge, this is the first report of haploid induction in Ae. tauschii.

Polyploidization and hybridization are the key components in plant evolution leading to the formation of new species/cultivars with improved traits. Allium L. (Amaryllidaceae) is an economically important genus encompassing great diversity in various morphological characters, particularly in its life forms along with bulbs and rhizomes. The conventional and modern crop improvement approaches have met with limited success in obtaining desired polyploidy / hybrid features in Allium since most of the species either pose crossing barriers or the resultant hybrids show infertility. In order to understand the possible role of chromosome dynamics, the present author studied the cytogenetic factors responsible for failure of polyploidization and hybridization events in an Allium hybrid “Negi-Nira” (A. fisutulosum × A.tuberosum, 2n = 24). The morphological characterization as well as genome organization of “Negi-Nira” has been discussed. It is emphasized that whereas genomic incompatibility may limit inter-specific crossability, the erratic meiosis further drives gametic sterility. The erratic meiosis-directed sterility was confirmed by the crossing experiment by pollinating “Negi-Nira” with the pollen of Welsh onion (donor). However, peculiar reproduction pattern through formation of bulbils (pseudobulbs) might occur consequent to artificial pollination stimulus in Allium. The immunolocalization of chromosome functional components including centromere-specific histone H3 (CENH3), ChIP-isolated centromeric DNA from Welsh onion, rDNA, 5S and tubulin evidently revealed the dynamic distribution pattern on the chromosomes of the onion hybrid “Negi-Nira”. The study suggests that the chromosome dynamics including erratic meiosis accompanied with irregularities in chromosomal functional components, centromeric proteins might have played a vital role in the development of crossing barriers among Allium species leading to the induction of peculiar reproduction ability in their hybrids.

Orchidaceae is a highly evolved and largest angiosperm family, which includes enormous number of species and their hybrids. Recent molecular cytogenetic studies of orchid hybrids have successfully started to reveal their origin and chromosome evolution. Here, we constructed BAC libraries of the two orchid plants, Neofinetia falcata and Rhynchostylis coelestis, as molecular cytogenetic tools, which can be used for chromosome-based comparisons of specific regions between different species and their hybrids chromosomes. A total of 21,000 and 10,600 BAC clones with average insert sizes of 74.6 and 50.8 kb were obtained for the N. falcata and R. coelestis, respectively. Random BAC FISH analyses of the two orchid species revealed distribution of some repetitive sequences in these orchid chromosomes. Thus, these BAC clones are useful resources for understanding the genomic organization of the orchid plants.