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, 10 (12), e0143861
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The Molecular Cytogenetic Characterization of Pistachio (Pistacia Vera L.) Suggests the Arrest of Recombination in the Largest Heteropycnotic Pair HC1

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The Molecular Cytogenetic Characterization of Pistachio (Pistacia Vera L.) Suggests the Arrest of Recombination in the Largest Heteropycnotic Pair HC1

Pedro J Sola-Campoy et al. PLoS One.

Abstract

This paper represents the first molecular cytogenetic characterization of the strictly dioecious pistachio tree (Pistacia vera L.). The karyotype was characterized by fluorescent in situ hybridization (FISH) with probes for 5S and 45S rDNAs, and the pistachio specific satellite DNAs PIVE-40, and PIVE-180, together with DAPI-staining. PIVE-180 has a monomeric unit of 176-178 bp and high sequence homology between family members; PIVE-40 has a 43 bp consensus monomeric unit, and is most likely arranged in higher order repeats (HORs) of two units. The P. vera genome is highly heterochromatic, and prominent DAPI positive blocks are detected in most chromosomes. Despite the difficulty in classifying chromosomes according to morphology, 10 out of 15 pairs (2n = 30) could be distinguished by their unique banding patterns using a combination of FISH probes. Significantly, the largest pair, designated HC1, is strongly heteropycnotic, shows differential condensation, and has massive enrichment in PIVE-40 repeats. There are two types of HC1 chromosomes (type-I and type-II) with differing PIVE-40 hybridization signal. Only type-I/II heterozygotes and type-I homozygotes individuals were found. We speculate that the differentiation between the two HC1 chromosomes is due to suppression of homologous recombination at meiosis, reinforced by the presence of PIVE-40 HORs and differences in PIVE-40 abundance. This would be compatible with a ZW sex-determination system in the pistachio tree.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Consensus sequence of monomeric units.
Consensus of PIVE-180 (A) and PIVE-40 (B), showing direct repeats (green), inverted repeats (blue), and short repeats (yellow).
Fig 2
Fig 2. Cells showing differential condensation of HC1 pair.
Root tip interphase (top left) and pro-metaphase (middle) of P. vera, (2n = 30) after DAPI staining. The differential condensation of HC1 pair is evidenced by large DAPI positive signal at interphase and bright, relatively short and compact chromosomes at pro-metaphase (arrow heads) while the smaller DAPI positive chromocentres at interphase are from the centromeres of the other chromosomes that are considerably longer at pro-metaphase. Bar represents 2.5 μm.
Fig 3
Fig 3. Karyotype of P. vera.
Karyotype root-tip metaphase chromosomes of P. vera (n = 15) stained with DAPI (A) showing two larger chromosomes (designated HC1) that are strongly heterochromatic. In situ hybridization using ribosomal DNA probes (red, 45S rDNA, pink, 5S rDNA), PIVE-180 (green) (B), and PIVE-40 (yellow, C). Bar represents 2.5 μm.
Fig 4
Fig 4. Idiogram of haploid chromosome complement of P. vera.
PIVE-40, PIVE-180, and 5S and 45S rDNA sites are shown. DAPI + regions and satellite chromosomes are also indicated. Chromosome types and sizes were constructed from the estimation of the centromere position.
Fig 5
Fig 5. Two types of HC1 chromosomes attending to PIVE-40 distribution.
Differential distribution of PIVE-40 repeats in the mitotic HC1 pair of P. vera. Bar represents 1 μm.

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Grant support

This work was supported by the project AGL2009-09094. P.J.S.-C. is an FPI scholar and R.N.-P. a Ramón y Cajal senior postdoctoral researcher (RYC-2011-08653), all funded by Ministerio de Ciencia e Innovación of Spain (http://www.idi.mineco.gob.es/portal/site/MICINN/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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