Carica papaya L. sex chromosome review and physical mapping of the serk 2, svp-like and mdar 4 sequences.

Physical mapping evidences the chromosome organization and structure. Despite the data about plant cytogenomics, physical mapping has been conducted from single-copy and/or low-copy genes for few species. Carica papaya cytogenomics has been accomplished from BAC-FISH and repeatome sequences. We aimed to map the serk 2, svp-like and mdar 4 sequences in C. papaya. The sequences were amplified and the amplicons sequenced, showing similarity in relation to serk 2, svp-like and mdar 4 genes. Carica papaya diploidy was confirmed and the mitotic chromosomes characterized. The chromosome 1 exhibited the secondary constriction pericentromeric to the centromere of the long arm. So, we concluded that it is the sex chromosomes. serk 2 was mapped in the long arm interstitial portion of the sex chromosomes, and the interphase nuclei showed two fluorescence signals. Considering these results and the sequencing data from the C. papaya sex chromosomes, svp-like and mdar 4 genes were mapped in the interstitial region of the sex chromosome long arm. Both sequences showed only one fluorescence signal in the interphase nuclei. The procedure adopted here can be reproduced for other single-copy and/or low-copy genes, allowing the construction of cytogenetic maps. In addition, we revisited the cytogenomics data about C. papaya sex chromosomes, presenting a revised point of view about the structure and evolution to these chromosomes.

Identification of novel small RNAs in extracellular vesicles produced by Actinobacillus pleuropneumoniae.

Extracellular vesicle (EV) production by bacteria is an important mechanism for microbial communication and host-pathogen interaction. EVs of some bacterial species have been reported to contain nucleic acids. However, the role of small RNAs (sRNAs) packaged in EVs is poorly understood. Here, we report on the RNA cargo of EVs produced by the pig pathogen Actinobacillus pleuropneumoniae, the causal agent of porcine pleuropneumonia, a disease which causes substantial economic losses to the swine industry worldwide. The EVs produced by aerobically and anaerobically grown bacteria were only slightly different in size and distribution. Total cell and outer membrane protein profiles and lipid composition of A. pleuropneumoniae whole cell extracts and EVs were similar, although EVs contained rough lipopolysaccharide compared to the smooth form in whole cells. Approximately 50% of Galleria mellonella larvae died after the injection of EVs. RNAseq, RT-PCR, protection from nuclease degradation, and database searching identified previously described and 13 novel A. pleuropneumoniae sRNAs in EVs, some of which were enriched compared to whole cell content. We conclude that A. pleuropneumoniae EVs contain sRNAs, including those known to be involved in virulence, and some with homologs in other Pasteurellaceae and/or non-Pasteurellaceae. Further work will establish whether the novel sRNAs in A. pleuropneumoniae EVs play any role in pathogenesis.

Embryonic abnormalities and genotoxicity induced by 2,4-dichlorophenoxyacetic acid during indirect somatic embryogenesis in Coffea.

Indirect somatic embryogenesis (ISE) is a morphogenetic pathway in which somatic cells form callus and, later, somatic embryos (SE). 2,4-dichlorophenoxyacetic acid (2,4-D) is a synthetic auxin that promotes the proliferation and dedifferentiation of somatic cells, inducing the ISE. However, 2,4-D can cause genetic, epigenetic, physiological and morphological disorders, preventing the regeneration and/or resulting abnormal somatic embryos (ASE). We aimed to evaluate the toxic 2,4-D effect during the Coffea arabica and C. canephora ISE, assessing the SE morphology, global 5-methylcytosine levels (5-mC%) and DNA damage. Leaf explants were inoculated in media with different 2,4-D concentrations. After 90 days, the friable calli were transferred to the regeneration medium, and the number of normal and abnormal SE was monthly counted. The increase of the 2,4-D concentration increased the number of responsive explants in both Coffea. At 9.06, 18.08 and 36.24 µM 2,4-D, C. arabica presented the highest values of responsive explants, differing from C. canephora. Normal and abnormal SE regeneration increased in relation to the time and 2,4-D concentration. Global 5-mC% varied at different stages of the ISE in both Coffea. Furthermore, the 2,4-D concentration positively correlated with global 5-mC%, and with the mean number of ASE. All ASE of C. arabica and C. canephora exhibited DNA damage and showed higher global 5-mC%. The allotetraploid C. arabica exhibited greater tolerance to the toxic effect of 2,4-D than the diploid C. canephora. We conclude that synthetic 2,4-D auxin promotes genotoxic and phytotoxic disorders and promotes epigenetic changes during Coffea ISE.

Popcorn (Zea mays L. var. Everta) haploids identified by Navajo phenotype and ploidy level.

For popcorn, obtaining and identifying haploids are still challenging steps. We aimed to induce and screen haploids in popcorn using the Navajo phenotype, seedling vigor, and ploidy level. We used the Krasnodar Haploid Inducer (KHI) in crosses with 20 popcorn source germplasms and five maize controls. The field trial design was completely randomized, with three replications. We assessed the efficacy of induction and identification of haploids based on the haploidy induction rate (HIR) and false positive and negative rates (FPR and FNR). Additionally, we also measured the penetrance of the Navajo marker gene (R1-nj). All putative haploids classified by the R1-nj were germinated together with a diploid sample and evaluated for false positives and negatives based on vigor. Seedlings from 14 females were submitted to flow cytometry to determine the ploidy level. The HIR and penetrance were analyzed by fitting a generalized linear model with a logit link function. The HIR of the KHI, adjusted by cytometry, ranged from 0.0 to 1.2%, with a mean of 0.34%. The average FPR from screening based on the Navajo phenotype was 26.2% and 76.4% for vigor and ploidy, respectively. The FNR was zero. The penetrance of R1-nj ranged from 30.8 to 98.6%. The average number of seeds per ear in temperate germplasm (76) was lower than that obtained in tropical germplasm (98). There is an induction of haploids in germplasm of tropical and temperate origin. We recommend the selection of haploids associated with the Navajo phenotype with a direct method of confirming the ploidy level, such as flow cytometry. We also show that haploid screening based on Navajo phenotype and seedling vigor reduces misclassification. The origin and genetic background of the source germplasm influence the R1-nj penetrance. Because the known inducers are maize, developing doubled haploid technology for popcorn hybrid breeding requires overcoming unilateral cross-incompatibility.

Genomic and epigenomic variation in Psidium species and their outcome under the yield and composition of essential oils.

Diploid and polyploid species derived from the euploid series x = 11 occur in the genus Psidium, as well as intraspecific cytotypes. Euploidy in the genus can alter the gene copy number, resulting in several "omics" variations. We revisited the euploidy, reported genomic (nuclear 2C value, GC%, and copy number of secondary metabolism genes) and epigenomic (5-mC%) differences in Psidium, and related them to essential oil yield and composition. Mean 2C values ranged from 0.90 pg (P. guajava) to 7.40 pg (P. gaudichaudianum). 2C value is intraspecifically varied in P. cattleyanum and P. gaudichaudianum, evidencing cytotypes that can be formed from euploid (non-reduced) and/or aneuploid reproductive cells. GC% ranged from 34.33% (P. guineense) to 48.95% (P. myrtoides), and intraspecific variations occurred even for species without 2C value intraspecific variation. Essential oil yield increased in relation to 2C value and to GC%. We showed that P. guajava (diploid) possesses two and P. guineense (tetraploid) four copies of the one specific TPS gene, as well as eight and sixteen copies respectively of the conserved regions that occur in eight TPS genes. We provide a wide "omics'' characterization of Psidium and show the outcome of the genome and epigenome variation in secondary metabolism.

In Vitro Polyploidization of Brassolaeliocattleya Hybrid Orchid.

The Cattleya (Orchidaceae-Laeliinae subtribe) intergeneric hybrids, such as Brassolaeliocattleya (Blc.), have great ornamental value, due to their compact-size, with large and high color diversity of flowers. Artificial induction of polyploidy brings agronomic, ornamental and genetic benefits to plants. Polyploidization efficiency depends on factors, such as the type of antimitotic, polyploidization method, concentrations, exposure times and type of explant. This study aimed to develop a protocol to polyploidize Blc. orchids, by testing two types of explants (seeds and protocorms), concentrations and exposure times to colchicine. The effects of colchicine on the in vitro development of explants were also investigated. The responses of explants to colchicine depended on the concentrations, exposure time and the interaction of these factors. Flow cytometric analysis evidenced high endopolyploidy and allowed the separation of polyploidized (4C, 8C and 16C peaks) from non-polyploidized (only 2C and 4C peaks) plants. The highest percentage of polyploid plants was regenerated from protocorms (16.4%) treated with colchicine instead of seeds (3.2%). Protocorms treated with colchicine at 500-750 µM for 18 h resulted in the best percentage of polyploidization. Additionally, in vitro natural polyploidization using protocorms was reported (11.5%). Cytological analyses allowed an estimation of the number of chromosomes of the parents (≡70), polyploidized (≡140) and non-polyploidized progeny (≡70).

Coffea cytogenetics: from the first karyotypes to the meeting with genomics.

MAIN CONCLUSION: Coffea karyotype organization and evolution has been uncovered by classical cytogenetics and cytogenomics. We revisit these discoveries and present new karyotype data. Coffea possesses ~ 124 species, including C. arabica and C. canephora responsible for commercial coffee production. We reviewed the Coffea cytogenetics, from the first chromosome counting, encompassing the karyotype characterization, chromosome DNA content, and mapping of chromosome portions and DNA sequences, until the integration with genomics. We also showed new data about Coffea karyotype. The 2n chromosome number evidenced the diploidy of almost all Coffea, and the C. arabica tetraploidy, as well as the polyploidy of other hybrids. Since then, other genomic similarities and divergences among the Coffea have been shown by karyotype morphology, nuclear and chromosomal C-value, AT and GC rich chromosome portions, and repetitive sequence and gene mapping. These cytogenomic data allowed us to know and understand the phylogenetic relations in Coffea, as well as their ploidy level and genomic origin, highlighting the relatively recent allopolyploidy. In addition to the euploidy, the role of the mobile elements in Coffea diversification is increasingly more evident, and the comparative analysis of their structure and distribution on the genome of different species is in the spotlight for future research. An integrative look at all these data is fundamental for a deeper understanding of Coffea karyotype evolution, including the key role of polyploidy in C. arabica origin. The 'Híbrido de Timor', a recent natural allotriploid, is also in the spotlight for its potential as a source of resistance genes and model for plant polyploidy research. Considering this, we also present some unprecedented results about the exciting evolutionary history of these polyploid Coffea.

Cadmium-mediated toxicity in plant cells is associated with the DCD/NRP-mediated cell death response.

Cadmium (Cd2+ ) is highly harmful to plant growth. Although Cd2+ induces programmed cell death (PCD) in plant cells, Cd2+ stress in whole plants during later developmental stages and the mechanism underlying Cd2+ -mediated toxicity are poorly understood. Here, we showed that Cd2+ limits plant growth, causes intense redness in leaf vein, leaf yellowing, and chlorosis during the R1 reproductive stage of soybean (Glycine max). These symptoms were associated with Cd2+ -induced PCD, as Cd2+ -stressed soybean leaves displayed decreased number of nuclei, enhanced cell death, DNA damage, and caspase 1 activity compared to unstressed leaves. Accordingly, Cd2+ -induced NRPs, GmNAC81, GmNAC30 and VPE, the DCD/NRP-mediated cell death signalling components, which execute PCD via caspase 1-like VPE activity. Furthermore, overexpression of the positive regulator of this cell death signalling GmNAC81 enhanced sensitivity to Cd2+ stress and intensified the hallmarks of Cd2+ -mediated PCD. GmNAC81 overexpression enhanced Cd2+ -induced H2 O2 production, cell death, DNA damage, and caspase-1-like VPE expression. Conversely, BiP overexpression negatively regulated the NRPs/GmNACs/VPE signalling module, conferred tolerance to Cd2+ stress and reduced Cd2+ -mediated cell death. Collectively, our data indicate that Cd2+ induces PCD in plants via activation of the NRP/GmNAC/VPE regulatory circuit that links developmentally and stress-induced cell death.

Short-term changes related to autotetraploidy in essential oil composition of Eucalyptus benthamii Maiden & Cambage and its applications in different bioassays.

Some forest trees have been polyploidized to improve their traits and to supply new germplasms for breeding programs. As trees have a long juvenile stage, the early characterization of the chromosome set doubling effects is crucial for previous selection. Thus, we aimed to characterize the chemical variability of essential oils from diploid and autotetraploid germplasms (autotetraploid A and B) of Eucalyptus benthamii, as well as to evaluate their larvicidal and allelopathic effects. Autotetraploid A showed a higher essential oil yield than diploid and autotetraploid B, which did not differ quantitatively. Aromadendrene, viridiflorol and α-pinene were the major compounds in the diploid essential oil. In contrast, compounds were present in autotetraploids, such as 1,8-cineole, limonene, α-terpineol, and α-terpinyl-acetate. Essential oils from the diploid at 50-200 ppm were twice as larvicidal than those from autotetraploids against Aedes aegypti larvae. Considering the phytotoxicity bioassays using Lactuca sativa, essential oils from both ploidy levels affected root growth. Moreover, the essential oils inhibited shoot growth at all concentrations tested (187.5; 375; 750; 1500; and 3000 ppm). Autotetraploid A and B had the same effect on shoot growth as glyphosate. The essential oils had no cytogenotoxic effect on root meristematic cells of L. sativa, whereas phytotoxic potential was identified mainly in shoot growth. This work demonstrated a dramatic change in secondary metabolism (terpene composition) related to an increase in the ploidy level in Eucalyptus germplasms. In addition, we report the novelty of the chemical composition of essential oils among germplasms and their potential use as larvicidal and post-emergence weed control agents.

Development of a robust hydroponic method for screening of sunflower (Helianthus annuus L.) accessions for tolerance to heat and osmotic stress.

Hydroponic systems are known to provide a platform for uniform growth conditions until the reproductive stage. However, many plant species, including sunflower, show poor growth and survivability under conventional hydroponic systems due to poor nutrient availability, hypoxia and algal contamination. Thus, we tested various hydroponic systems to select a hydroponic system suitable for screening of sunflower germplasm. Sunflower accessions showed better growth and leaf gas exchange in newly-designed over conventional hydroponic systems. Selected hydroponic systems were further engaged in sunflower accession screening under heat and osmotic stress in a two-pan system (210 cm × 60 cm). Heat stress treatment was applied by growing sunflower germplasm at 42 °C and osmotic stress by adding polyethylene glycol 8000 which decreased the osmotic potential to - 0.6 MPa. There was significant variability among the sunflower accessions for their ability to survive under stress. Accessions such as C-2721 (43%), C-291 (46%) and D-14 (43%) had lower cell membrane injury percentage under osmotic stress and high seedling survivability (60‒80%) under heat stress when compared with susceptible accessions. Moreover, resistant accessions exhibited greater cuticular waxes and root length but lower transpiration losses. The newly designed hydroponic platform proved reliable for the selection of resistant sunflower accessions. Selected parental lines were validated by assessing their hybrids under field trials across two seasons under water and temperature stress during the reproductive phase (autumn). Hybrid H3 obtained by crossing drought and heat resistant parents had the highest seed yield and water use efficiency.

Global 5-methylcytosine and physiological changes are triggers of indirect somatic embryogenesis in Coffea canephora.

Indirect somatic embryogenesis (ISE) establishment for Coffea species started in the 1970s. Since then, intraspecific variations in the morphogenic pathway have been reported, even in the common environmental condition in vitro. Several authors have suggested that these variations are the result of genetic, epigenetic, and/or physiological events, highlighting the need for investigations to know the causes. Along these lines, this study aimed to investigate and describe, for the first time, the global 5-methylcytosine and physiological changes that occur in the cells of the aggregate suspensions of Coffea canephora during proliferation and somatic embryo regeneration steps. The cell proliferation step was characterized by increase in cell mass in all subcultures; relatively low mean values of global 5-methylcytosine (5-mC%), abscisic acid (ABA), and indole-3-acetic acid (IAA); high mean value of 1-aminocyclopropane-1-carboxylic acid (ACC, an ethylene precursor); and increase followed by decrease in spermidine (Spd, a polyamine) level. Therefore, these epigenetic and physiologic aspects promoted the cell proliferation, which is fundamental for ISE. In turn, the somatic embryo regeneration was correlated with global 5-mC% and physiological changes. The competence acquisition, determination, and cell differentiation steps were marked by increases in mean values of 5-mC%, IAA and ABA, and decreases in ACC and Spd, evincing that these changes are the triggers for regeneration and maturation of somatic embryos. Therefore, dynamic and coordinated epigenetic and physiologic changes occur in the cells of the aggregate suspensions during the C. canephora ISE in liquid system.

A Heterochromatic Knob Reducing the Flowering Time in Maize.

Maize flowering time is an important agronomic trait, which has been associated with variations in the genome size and heterochromatic knobs content. We integrated three steps to show this association. Firstly, we selected inbred lines varying for heterochromatic knob composition at specific sites in the homozygous state. Then, we produced homozygous and heterozygous hybrids for knobs. Second, we measured the genome size and flowering time for all materials. Knob composition did not affect the genome size and flowering time. Finally, we developed an association study and identified a knob marker on chromosome 9 showing the strongest association with flowering time. Indeed, modelling allele substitution and dominance effects could offer only one heterochromatic knob locus that could affect flowering time, making it earlier rather than the knob composition.

Repetitive sequences and structural chromosome alterations promote intraspecific variations in Zea mays L. karyotype.

LTR-retrotransposons, knobs and structural chromosome alterations contribute to shape the structure and organization of the Zea mays karyotype. Our initial nuclear DNA content data of Z. mays accessions revealed an intraspecific variation (2 C = 2.00 pg to 2 C = 6.10 pg), suggesting differences in their karyotypes. We aimed to compare the karyotypes of three Z. mays accessions in search of the differences and similarities among them. Karyotype divergences were demonstrated among the accessions, despite their common chromosome number (2n = 20) and ancestral origin. Cytogenomic analyses showed that repetitive sequences and structural chromosome alterations play a significant role in promoting intraspecific nuclear DNA content variation. In addition, heterozygous terminal deletion in chromosome 3 was pointed out as a cause of lower nuclear 2 C value. Besides this, translocation was also observed in the short arm of chromosome 1. Differently, higher 2 C value was associated with the more abundant distribution of LTR-retrotransposons from the family Grande in the karyotype. Moreover, heteromorphism involving the number and position of the 180-bp knob sequence was found among the accessions. Taken together, we provide insights on the pivotal role played by repetitive sequences and structural chromosome alterations in shaping the karyotype of Z. mays.

Author Correction: Repetitive sequences and structural chromosome alterations promote intraspecific variations in Zea mays L. karyotype.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Plant Chromosome-Specific Probes by Microdissection of a Single Chromosome: Is That a Reality?

Painting plant chromosomes through chromosomal in situ suppression (CISS) hybridization has long been considered impracticable. Seeking to build specific and complex probes from a single microdissected chromosome, we employed human chromosomes as models to standardize all the necessary steps for application in plants. Human metaphases were used to define the adequate conditions for microdissection, chromosome DNA amplification and labeling through degenerate oligonucleotide-primed PCR, and in situ hybridization stringency. Subsequently, these methodologies were applied in the plant species Zea mays (chromosome 1) and Capsicum annuum (chromosome 7 or 8). The high quality of human and plant cytogenetic preparations and the meticulous standardization of each step, especially the most critical ones - microdissection and first round of DNA amplification - were crucial to eliminate the signs of non-specific hybridization and for direct application in plants. By overcoming these challenges, we obtained chromosome-specific probes, which allowed to achieve a clear and uniform painting of the entire target chromosomes with little or no background, evidencing their complexity and specificity. Despite the high amount of ubiquitous repetitive sequences in plant genomes, the main drawback for chromosome painting, we successfully employed our methodology on two plant species. Both have more than 80% repetitive sequences, which is compared to the human genome (66-69%). This is the first time that plant chromosome-specific probes were successfully obtained from a single A mitotic or meiotic microdissected chromosome. Thereby, we assume that chromosome painting through microdissection and CISS hybridization can now be considered a reality in the field of plant cytogenetics.

Autotetraploid Coffea canephora and Auto-Alloctaploid Coffea arabica From In Vitro Chromosome Set Doubling: New Germplasms for Coffea.

Polyploidy is more than two chromosomal sets per nucleus, as the allotetraploid Coffea arabica. Due to allotetraploidy, C. arabica shows different phenotypes compare to diploid Coffea species, highlighting by beverage quality produced from its grains. Looking for the possibility of new phenotypes coupled with economic feature, considerable progress since 60's was reached for synthetic chromosome set doubling (CSD) in vitro, involving especially the antitubulin compounds, biological material, and used tissue culture pathway as the indirect somatic embryogenesis (ISE). Here, we aimed to regenerate autotetraploid and auto-alloctaploid plantlets of Coffea canephora and C. arabica, respectively, from a novel in vitro CSD procedure for Coffea. Exploring the ISE pathway, we treated the cellular aggregate suspensions (CAS) with 0.0 (control), 0.5, 1.5, or 2.5 mM of colchicine solution for 48, 72, or 96 h and maintained in liquid medium under constant orbital shaking. After transferring the CAS to semisolid media for somatic embryo regeneration, we considered it as cellular mass. Mature cotyledonary somatic embryos were only regenerated from cellular masses treated with 2.5 mM/48 h and 2.5 mM/72 h for C. canephora and with 0.5 mM/48 h for C. arabica. Evaluating the DNA ploidy level and the chromosome counting revealed that 36 (34.9%) plantlets of C. canephora were autotetraploids (4C = 2.86 pg, 2n = 4x = 44) and 61 (21.1%) of C. arabica were auto-alloctaploids (4C = 5.24 pg, 2n = 8x = 88). The CSD procedure, exploring the CAS proliferation and ISE pathway, promoted whole-genome duplication and resulted in a relatively high number of solid polyploids of both Coffea species. Due to distinct responses, DNA sequence fidelity (genetic) and global level of 5-methylcytosine (epigenetic) were evaluated. We observed that the increase of 5-methylcytosine levels was associated with somatic embryo regeneration from cells showing DNA sequence fidelity for the tested SSR primers. In conclusion, the adopted procedure for in vitro CSD is reproducible for induction, regeneration and propagation of Coffea polyploids and potentially other shrubbery and woody species. In view of the novelty of this procedure to generate new germplasm, we show the key issues and the steps of the CSD procedure.

Genetic diversity and karyotype of Pitcairnia azouryi: an endangered species of Bromeliaceae endemic to Atlantic Forest inselbergs.

Plant species of various families, such as those of Bromeliaceae, occur on inselbergs where they are subject to geographic isolation and environmental conditions that can lead to genetic erosion. This, in turn, can result in the loss of natural populations due to homozygosis, or changes in ploidy that may lead to reproductive isolation. The genetic diversity of five natural populations of Pitcairnia azouryi was measured using nine microsatellite markers transferred from P. albiflos and P. geyskesii. Chromosome numbers and nuclear DNA content were also evaluated. The results indicated moderate genetic differentiation among populations (FST = 0.188), and significant gene flow (Nm = 1.073) in four of the five populations. P. azouryi has, predominantly, 2n = 50 chromosomes and DNA content of 2C = 1.16 pg, but the tetraploid condition was found (2n = 100 and 2C = 2.32 pg) in seedlings of an individual of the most geographically isolated population. The moderate level of genetic structuring observed for P. azouryi seems to be related to its disjoint geographical distribution and the locally aggregated spatial structure of the populations, which are isolated from each other, hindering the inter and intrapopulational gene flow. This interpretation was also evidenced by the mantel test (r = 0.777, P < 0.05). The occurrence of diploid individuals with tetraploid seedlings is indicative of events of eupolyploidization, possibly due to the environmental conditions of this geographically isolated population.

Updating the maize karyotype by chromosome DNA sizing.

The karyotype is a basic concept regarding the genome, fundamentally described by the number and morphological features of all chromosomes. Chromosome class, centromeric index, intra- and interchromosomal asymmetry index, and constriction localization are important in clinical, systematic and evolutionary approaches. In spite of the advances in karyotype characterization made over the last years, new data about the chromosomes can be generated from quantitative methods, such as image cytometry. Therefore, using Zea mays L., this study aimed to update the species' karyotype by supplementing information on chromosome DNA sizing. After adjustment of the procedures, chromosome morphometry and class as well as knob localization enabled describing the Z. mays karyotype. In addition, applying image cytometry, DNA sizing was unprecedentedly measured for the arms and satellite of all chromosomes. This way, unambiguous identification of the chromosome pairs, and hence the assembly of 51 karyograms, were only possible after the DNA sizing of each chromosome, their arms and satellite portions. These accurate, quantitative and reproducible data also enabled determining the distribution and variation of DNA content in each chromosome. From this, a correlation between DNA amount and total chromosome length evidenced that the mean DNA content of chromosome 9 was higher than that of chromosome 8. The chromosomal DNA sizing updated the Z. mays karyotype, providing insights into its dynamic genome with regards to the organization of the ten chromosomes and their respective portions. Considering the results and the relevance of cytogenetics in the current scenario of comparative sequencing and genomics, chromosomal DNA sizing should be incorporated as an additional parameter for karyotype definition. Based on this study, it can be affirmed that cytogenetic approaches go beyond the simple morphological description of chromosomes.

First karyotype description and nuclear 2C value for Myrsine (Primulaceae): comparing three species.

Cytogenetic studies in Primulaceae are mostly available for herbaceous species, and are focused on the chromosome number determination. An accurate karyotype characterization represents a starting point to know the morphometry and class of the chromosomes. Comparison among species within Myrsine, associating these data with the nuclear 2C value, can show changes that led the karyotype evolution. Here, we studied three Myrsine species [Myrsine coriacea (Swartz, 1788) Brown ex Roemer et Schultes, 1819, Myrsine umbellata Martius, 1841 and Myrsine parvifolia Candolle, 1841] that show different abilities to occupy the varied types of vegetation within the Brazilian Atlantic Forest. Cytogenetic characterization showed some individuals with 2n = 45 chromosomes for Myrsine parvifolia and Myrsine coriacea, with most individuals of the three species having 2n = 46. The first karyograms for Myrsine were assembled and presented morphologically identical and distinct chromosome pairs. In addition, differences in the mean 2C nuclear value and chromosome morphometry were found. Therefore, the first description of the Myrsine karyotype has been presented, as well as the nuclear 2C value. The procedures can be applied to other Myrsine species for future investigations in order to better understand its effects on the differential spatial occupation abilities shown by the species in Brazilian Atlantic Forest.

Karyotype characterization and comparison of three hexaploid species of Bromus Linnaeus, 1753 (Poaceae).

Chromosome morphometry and nuclear DNA content are useful data for cytotaxonomy and to understand the evolutionary history of different taxa. For the genus Bromus Linnaeus, 1753, distinct ploidy levels have been reported, occurring from diploid to duodecaploid species. The geographic distribution of Bromus species has been correlated with chromosome number and ploidy level. In this study, the aims were to determine the nuclear genome size and characterize the karyotype of the South American Bromus species: Bromus auleticus Trinius ex Nees, 1829, Bromus brachyanthera Döll, 1878 and Bromus catharticus Vahl, 1791. The mean nuclear 2C value ranged from 2C = 12.64 pg for B. catharticus to 2C = 17.92 pg for B. auleticus, meaning a maximum variation of 2C = 5.28 pg, equivalent to 41.70%. Despite this significant difference in 2C value, the three species exhibit the same chromosome number, 2n = 6x = 42, which confirms their hexaploid origin. Corroborating the genome size, the chromosome morphometry (total, short- and long-arm length) and, consequently, the class differed among the karyotypes of the species. Based on the first karyograms for these Bromus species, some morphologically similar and several distinct chromosome pairs were found. Therefore, the karyotype characterization confirmed the hexaploid origin of the studied Bromus species, which differ in relation to the karyogram and the nuclear 2C value. Considering this, cytogenetics and flow cytometry can be used to discriminate Bromus species, contributing to taxonomy and systematic studies and providing information on the evolutionary history of this taxa.