The Cytogenetic Map of the Poncirus trifoliata (L.) Raf.—A Nomenclature System for Chromosomes of All Citric Species

Abstract

A cytogenetic map was established for the trifoliate orange, Poncirus trifoliata. Chromosome size, centromere position and CMA + heterochromatin content were determined for each chromosome pair, together with the position of BAC clones previously described as chromosome-specific markers. Although P. trifoliata is a true biological species, heteromorphisms for the size of the heterochromatic bands in two chromosome pairs were observed. A minimum set of four BACs was proposed for chromosome identification in P. trifoliata, as well as a chromosome nomenclature that can be applied to all citrus species. The Ctv locus was assigned to chromosome 9 and the remaining linkage groups can now be integrated to this physical map. This standard nomenclature for trifoliate orange will be valuable for genome-sequencing projects in all citrus species.

Chromosome homeologies and high variation in heterochromatin distribution between Citrus L. and Poncirus Raf. as evidenced by comparative cytogenetic mapping

“…1e and f): BAC 21L13, on chromosome 2, co-localized with the CMA + band; BACs 02C12 and 20C13, on chromosome 4, were located in the interstitial region of the short arm and adjacent to the CMA + band on the opposite arm, Silva et al (2011) b 0 represents the telomere of the short arm and 1 represents the telomere of the long arm respectively; the 5S rDNA, on chromosome 5; and BACs 24E07, 55B01, and 59C23 on chromosome 9, co-localized in the interstitial region of the long arm ( Fig. 1g and h).…”

“…Twenty-five BACs selected from the P. trifoliata genomic library (Yang et al 2001) and previously mapped on this species (Moares et al 2008;Silva et al 2011;A.P. Moraes, unpublished data), as well as the 5S rDNA clone (D2) of Lotus japonicus (Pedrosa et al 2002) were used as probes.…”

“…All probes were labeled by nick translation (Roche and Invitrogen) using Cy3-dUTP (GE). The procedure and conditions for FISH followed Jiang et al (1995) with minor modifications and stringency of 73%, as described by Silva et al (2011). When necessary, DNA blocker (C o t-1 fraction of P. trifoliata genomic DNA) was used and prepared according to Zwick et al (1997).…”

“…To establish the relative position of each BAC clone along the chromosome, BAC signals were measured relative to telomeres in 15 chromatids using Image Tool 3.0 software. The chromosomes were numbered according to the homeology to P. trifoliata chromosomes (Silva et al 2011) and were drawn in the same scale considering the total genome sizes of both species in Mbp.…”

“…The authors mapped 13 BACs from a genomic library of P. trifoliata, in addition to CMA/ DAPI staining and rDNA localization, allowing the identification of the nine chromosome pairs and the mapping of the citrus tristeza virus (CTV) resistance locus. This map has been recently improved by Silva et al (2011).…”