Telomeres and Subtelomeres Dynamics in the Context of Early Chromosome Interactions During Meiosis and Their Implications in Plant Breeding

Genomic architecture facilitates chromosome recognition, pairing, and recombination. Telomeres and subtelomeres play an important role at the beginning of meiosis in specific chromosome recognition and pairing, which are critical processes that allow chromosome recombination between homologs (equivalent chromosomes in the same genome) in later stages. In plant polyploids, these terminal regions are even more important in terms of homologous chromosome recognition, due to the presence of homoeologs (equivalent chromosomes from related genomes). Although telomeres interaction seems to assist homologous pairing and consequently, the progression of meiosis, other chromosome regions, such as subtelomeres, need to be considered, because the DNA sequence of telomeres is not chromosome-specific. In addition, recombination operates at subtelomeres and, as it happens in rye and wheat, homologous recognition and pairing is more often correlated with recombining regions than with crossover-poor regions. In a plant breeding context, the knowledge of how homologous chromosomes initiate pairing at the beginning of meiosis can contribute to chromosome manipulation in hybrids or interspecific genetic crosses. Thus, recombination in interspecific chromosome associations could be promoted with the aim of transferring desirable agronomic traits from related genetic donor species into crops. In this review, we summarize the importance of telomeres and subtelomeres on chromatin dynamics during early meiosis stages and their implications in recombination in a plant breeding framework.

Chromosome Manipulation for Plant Breeding Purposes

The transfer of genetic variability from related species into crops has been a main objective for decades in breeding programs. Breeders have used interspecific genetic crosses and alien introgression lines to achieve this goal, but the success is always dependent on the interspecific chromosome associations between the alien chromosomes and those from the crop during early meiosis. In this Special Issue, the strength of chromosome manipulation in a breeding framework is revealed through research and review papers that combine molecular markers, cytogenetics tools and other traditional breeding techniques. The papers and reviews included in this Special Issue “Chromosome manipulation for plant breeding purposes” describe the development and/or characterization of new plant material carrying desirable traits and the study of chromosome associations and recombination during meiosis. New tools to facilitate the transfer of desired traits from a donor species into a crop can be developed by expanding the knowledge of chromosome associations during meiosis.

Pengaruh Kejutan Suhu Panas Dan Lama Waktu Setelah Pembuahan Terhadap Daya Tetas Dan Abnormalitas Larva Ikan Nila (Oreochromis niloticus) [The Thermal Temperature Shock And Time After Fertilization In Hatching Rate And Abnormality Of Nile Fish (Oreochromis niloticus) ]

The chromosome manipulation in fish is one of the strategy that will be used to produce of the high generation and good quality in its genetics, as follow fast to grow, disease resistant, high survival, tolerate with environment exchange and easy to be cultured. One of manipulation chromosome the method in fish used thermal temperature shock. The aim of the study was to know the thermal temperature shock and the time after fertilization forward hatching rate and abnormality of nile fish larvae and also to know the thermal temperature shock and the time after fertilization that resulted the best hatching rate and abnormality in nile fish larvae. The method was Factorial Completed Randomized Design as experimental design. The treatment used temperatures shock were 40ºC, 41ºC and 42ºC as long as 2,5 minutes, with the time of 80, 85 and 90 minutes after fertilization, each treatment was four replications. The primary parameter was hatching rate and abnormality of nile fish larvae and the secondary parameter were fertilization and water quality. The result showed that the thermal temperature shock was significantly influenced to hatch rate and abnormality, but the time of shocking after fertilization and the interaction between them showed were not significantly influenced to hatch rate and abnormality. The highest of hatching rate and abnormality percentage was showed by the treatment with shocking 40°C was 90,77 percent and 2,60 percent.

Chromosome aberrations induced by zebularine in triticale

Chromosome engineering is an important approach for generating wheat germplasm. Efficient development of chromosome aberrations will facilitate the introgression and application of alien genes in wheat. In this study, zebularine, a DNA methylation transferase inhibitor, was successfully used to induce chromosome aberrations in the octoploid triticale cultivar Jinghui#1. Dry seeds were soaked in zebularine solutions (250, 500, and 750 μmol/L) for 24 h, and the 500 μmol/L treatment was tested in three additional treatment times, i.e., 12, 36, and 48 h. All treatments induced aberrations involving wheat and rye chromosomes. Of the 920 cells observed in 67 M1 plants, 340 (37.0%) carried 817 aberrations with an average of 0.89 aberrations per cell (range: 0–12). The aberrations included probable deletions, telosomes and acentric fragments (49.0%), large segmental translocations (28.9%), small segmental translocations (17.1%), intercalary translocations (2.6%), long chromosomes that could carry more than one centromere (2.0%), and ring chromosomes (0.5%). Of 510 M2 plants analyzed, 110 (21.6%) were found to carry stable aberrations. Such aberrations included 79 with varied rye chromosome numbers, 7 with wheat and rye chromosome translocations, 15 with possible rye telosomes/deletions, and 9 with complex aberrations involving variation in rye chromosome number and wheat–rye translocations. These indicated that aberrations induced by zebularine can be steadily transmitted, suggesting that zebularine is a new efficient agent for chromosome manipulation.

1 REPLICATION OF SOMATIC MICRONUCLEI IN BOVINE OOCYTES

Microcell-mediated chromosome transfer was developed to introduce a low number of chromosomes into a host cell (Fournier and Ruddle 1977 PNAS 74, 319–323). As a first approach to individual chromosome manipulation, we designed a new technique that consists of injecting a micronucleus into an enucleated oocyte to replicate a low number of chromosomes. Additionally, we studied the capability of such micronuclei to be marked with a transgene. To this aim, micronuclei from adult bovine fibroblasts were produced by incubation in 0.05 μg mL–1 of demecolcine for 48 h followed by 2 mg mL–1 of mitomycin for 2 h. Cells were finally treated with 10 μg mL–1 of cytochalasin B for 1 h. The cumulus-oocyte complexes aspirated from slaughtered cow ovaries were in vitro-matured under standard conditions for 21 h. MII oocytes were mechanically enucleated and injected with somatic micronucleus, which were previously exposed (Mi*) or not (Mi) to 50 ng μL–1 of pCX-EGFP in 10% PVP. Sham and parthenogenetic (PA*) controls were injected with 50 ng μL–1 of pCX-EGFP in 10% PVP. A PA control was also included. After 2 h, oocytes and reconstructed embryos were activated by incubation in 5 μM ionomycin for 4 min + 1.9 mM 6-DMAP for 3 h. Embryos were cultured in SOF. Cleavage stage and egfp expression were evaluated at Day 2 and 4 of IVC, respectively. At Day 2, some Mi and PA embryos were fixed and stained with DAPI. Nuclei were visualised under blue light (488 nm). Cleaved embryos with more than one nucleus were considered to have replicated their DNA. At Day 2, Mi and PA embryos were karyotyped. An IVF group was also included (Brackett and Oliphant protocol, 1975). Briefly, cleaved embryos were treated with 1.25 μg mL–1 of colchicine for 6 h. After Carnoy fixation, they were stained with Giemsa to determine the chromosomal complement of each blastomere. Embryos were classified as follows: less than 15 chromosomes, euploid (1n and 2n) and others (4n, mixoploid and aneuploid). Differences among treatments were determined by Fisher's exact test (P ≤ 0.05). The Mi*, PA* and PA groups showed higher cleavage rates than the Mi treatment [93/108 (86.1%), 111/136 (81.6%) and 160/186 (86%), respectively vs 89/131 (67.9%); P ≤ 0.05]. Cleavage rates of the Sham* group [78/105 (74.3%)] did not differ from Mi and PA* treatments (P ≤ 0.05). Interestingly, a low number of Mi* embryos showed egfp expression (2.2%). Expression levels were significantly lower than those of the PA* group (38.7%) and did not differ from the Sham control (0%; P ≤ 0.05). Although rates of Mi embryos with more than 1 nucleus (63.6%, n = 22) were lower than those for the PA group (100%, n = 28), DAPI staining confirmed replication of micronuclei. Karyotype analysis revealed that 100% of Mi evaluated embryos (n = 11) had less than 15 chromosomes per blastomere (varying from 1 to 13), whereas none of IVF and PA controls showed such results (P ≤ 0.05). Rates of euploid embryos were 75 (n = 20) and 45% (n = 20) for IVF and PA groups, respectively. In conclusion, we have developed a new method for somatic micronuclei, which could be a useful tool to transfer a small number of specific chromosomes and to target transgenesis to a reduced area of the genome.