Abstract
Jatropha (Jatropha curcas) is an oil-bearing plant used for biodiesel production. Construction of its standard karyotype and identification of the euchromatin/heterochromatin distribution associated with gene expression and meiotic recombination are essential to fully characterize its genome. Here, we developed a J. curcas karyotype based on meiotic pachytene chromosomes. In addition, a karyotype of J. integerrima, a useful species for jatropha breeding, was also constructed. Five out of eleven J. curcas chromosomes were metacentric, but only two were metacentric in J. integerrima. Almost all of the heterochromatin was distributed around the pericentric regions. The interstitial and distal regions were euchromatic without heterochromatic knobs, except for small heterochromatin regions associated with the subtelomeric repeat sequence JcSat1. These pericentric heterochromatin distribution patterns, together with chromosome structure data and the results of FISH probing with rDNA and JcSat1, allowed us to classify all chromosomes of both species. The two species had two 35S rDNA loci and one 5S rDNA locus; one 35S rDNA locus in J. integerrima was located on the interstitial region of the short arms. In addition, JcSat1 was found at only the heterochromatic ends of the J. curcas chromosome, not the J. integerrima chromosome. Despite the same chromosome number, the two pachytene chromosome-based karyotypes suggest variation in chromosome structure and distribution of repetitive DNAs in these two species.
Highlights
Jatropha curcas is known as physic nut or jatropha (Euphorbiaceae) and has become one of the most important oilseed crops in the world
To analyze the cytological features of two Jatropha species, we observed well-spread meiotic pachytene chromosomes stained by DAPI and fluorescence in situ hybridization (FISH) signals of repetitive DNAs
The vertical lengths of the buds were 2–2.5 mm in J. curcas and 2.5–3 mm in J. integerrima, and pachytene chromosomes with a length of 40–70 μm were suitable for observing the chromatin patterns
Summary
Jatropha curcas is known as physic nut or jatropha (Euphorbiaceae) and has become one of the most important oilseed crops in the world. To analyze the cytological features of two Jatropha species, we observed well-spread meiotic pachytene chromosomes stained by DAPI and FISH signals of repetitive DNAs. Our observations revealed an overconcentration of heterochromatin at the centric region and a variation in the locations of 35S rDNA and JcSat1. FISH and GISH were performed using root tip samples of the F1 plant to observe the presence of rDNA and JcSat1 repeats on the chromosomes of each parental species.
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