Karyotype variability in tropical maize sister inbred lines and hybrids compared with KYS standard line

Abstract

Maize karyotype variability has been extensively investigated. The identification of maize somatic and pachytene chromosomes has improved with the development of fluorescence in situ hybridization (FISH) using tandemly repeated DNA sequences as probes. We identified the somatic chromosomes of sister inbred lines that were derived from a tropical flint maize population (Jac Duro [JD]), and hybrids between them, using FISH probes for the 180-bp knob repeat, centromeric satellite (CentC), centromeric satellite 4 (Cent4), subtelomeric clone 4-12-1, 5S ribosomal DNA and nucleolus organizing region DNA sequences. The observations were integrated with data based on C-banded mitotic metaphases and conventional analysis of pachytene chromosomes. Heterochromatic knobs visible at pachynema were coincident with C-bands and 180-bp FISH signals on somatic chromosomes, and most of them were large. Variation in the presence of some knobs was observed among lines. Small 180-bp knob signals were invariant on the short arms of chromosomes 1, 6, and 9. The subtelomeric 4-12-1 signal was also invariant and useful for identifying some chromosomes. The centromere location of chromosomes 2 and 4 differed from previous reports on standard maize lines. Somatic chromosomes of a JD line and the commonly used KYS line were compared by FISH in a hybrid of these lines. The pairing behavior of chromosomes 2 and 4 at pachytene stage in this hybrid was investigated using FISH with chromosome-specific probes. The homologues were fully synapsed, including the 5S rDNA and CentC sites on chromosome 2, and Cent4 and subtelomeric 4-12-1 sites on chromosome 4. This suggests that homologous chromosomes could pair through differential degrees of chromatin packaging in homologous arms differing in size. The results contribute to current knowledge of maize global diversity and also raise questions concerning the meiotic pairing of homologous chromosomes possibly differing in their amounts of repetitive DNA.

Alterations in Heterochromatic Knobs in Maize Callus Culture by Breakage-Fusion-Bridge Cycle and Unequal Crossing Over

“…It is well known that maize races vary in the number and size of knobs [McClintock et al, 1981]. For example, in the 132331 line used in the present work, a large knob is present in the short arm of chromosome 9, while in the temperate line KYS, the same knob is very small [Mondin et al, 2014]. The objective of the present work is not to discuss the origin of knob variability, but it is interesting to emphasize here that unequal crossing over would be one of the mechanisms that would have given origin to the variability of knob sizes during the evolution of maize races.…”

“…K6L2, K6L3, K8L1, and K8L2 refer to different knob positions on chromosomes 6 and 8, according to the literature [McClintock et al, 1981]. The 13342/5 line was derived from the tropical variety Jac Duro (JD), and the karyotype of a S6 progeny (133425) of this line was characterized by Mondin et al [2014]. In a previous cytogenetic analysis of the 12-F culture, an amplification of K7L was detected in a cell line designated 1-MS2, and in plants regenerated from cell line 2-N6, chromosome 7 was not altered.…”

Maize Chromosome Abnormalities and Breakage-Fusion-Bridge Cycles in Callus Cultures

“…The callus culture was induced from a hybrid between two sister inbred lines derived from a tropical maize variety (Jac Duro [JD]). These JD lines possessed the same knob composition: K6 L2, K6 L3, K7S, K7L, K8 L1, K8 L2, and K9S [8,20]. K refers to knob, the number identifies the chromosome, and S refers to short arm and L to long arm.…”

“…The characterization of meiotic and somatic chromosomes was improved by fluorescence in situ hybridization (FISH) using as probes repeated DNA sequences and genes, thus allowing the study of the molecular structure of chromosome components, such as centromere, neocentromere, B chromosome heterochromatic knobs, and gene mapping [12][13][14][15][16][17][18][19][20].…”

Breakage–fusion–bridge cycles and de novo telomere formation on broken chromosomes in maize callus cultures

“…K6L2, K6L3, K8L1 and K8L2 refer to different knob positions on chromosomes 6 and 8, according to the literature (McClintock et al, 1981). These lines were derived from the tropical flint variety Jac Duro (JD lines), and their karyotypes were characterized by Mondin et al (2014). In this material, the chromosome 7 has a terminal knob on the short arm (K7S) and an interstitial knob on the long arm (K7L), but in several cells of the 3-57 culture, one altered chromosome 7 with two knobs on the short arm was observed (Fluminhan et al, 1996).…”