Elsevier

Plant Science

Volume 174, Issue 6, June 2008, Pages 613-617
Plant Science

Genome size, base composition and karyotype of Jatropha curcas L., an important biofuel plant

https://doi.org/10.1016/j.plantsci.2008.03.010Get rights and content

Abstract

In this report, we present the genome size, the base composition and the karyotype of Jatropha curcas L., which is becoming an important oleaginous crop in tropical areas for biofuel production. The genome size and the base composition were obtained by flow cytometry of G0/G1 nuclei stained with propidium iodide (for genome size), DAPI (for AT) and chromomycin A3 (for GC), respectively. The karyotype was obtained by root-tip (i) incubation with amiprophos-methyl (microtubule inhibitor), (ii) digestion in enzymatic solution, (iii) squashing on glass slides, (iv) fixation and (v) coloration in Giemsa solution. We found that the genome of J. curcas is relatively small and in the same size range as that of rice. The flow cytometry indicates an average 2C value of 0.85 pg and an average base composition of 38.7% GC. The karyotype of J. curcas is made up of 22 relatively small metacentric and submetacentric chromosomes whose size range from 1.71 to 1.24 μm. The possibility of a polyploidization event in the evolutionary history of J. curcas is discussed.

Introduction

Jatropha curcas (Euphorbiaceae) or simply Jatropha (also known as Pinhão-Manso in Portuguese), is a tree thought to be native from Central America [1] and possibly from Brazil. It is now almost pantropical and has been listed as a weed in Australia, South Africa, India, Brazil, Fiji, Honduras, Panama, El Salvador, Jamaica, Puerto Rico, and other parts of Caribbean.

There is growing interest in the use of J. curcas oil to alleviate the energy crisis. J. curcas oil is relatively simple to convert to biodiesel by chemical [2] or biological transesterification [3]. In addition to the low production cost, J. curcas biofuel has been reported to be non-toxic, clean and eco-friendly [4].

This euphorbia is a “drought resistant” plant which grows on wasteland and could easily be cultivated by low income farmers. It is grown as a shrub and thought that it could benefit energy provision to remote areas. In this respect, J. curcas is considered a strategic crop for countries such as Brazil or India. After irrigation, fertilization and soil tillage, J. curcas may reach the flowering stage within 1 year of planting and produce an abundant crop. Although it may look promising, it lacks an improved germplasm. Consequently, several pests and diseases have already been observed at the industrial production level. (personal communication from Nagashi Tominaga, NNE Minas Agro Florestal ltda, Brazil). In addition, the J. curcas oilcake is not suitable for feeding livestock because of toxic compounds such as phorbol ester and curcin [5], [6], [7], [8], [9].

While J. curcas germplasm is being harvested all over the world with the purpose of crop improvement, little is known about its genome. In this study, we measured the genome size and base composition of J. curcas by flow cytometry and mounted its karyotype from root-tip chromosomes.

Section snippets

Plant material

J. curcas seeds from the progenitor ‘Gonçalo’ were kindly provided by Nagashi Tominaga (NNE Minas Agro Florestal Ltda, Janaúba, MG, Brazil). Seeds of Raphanus sativus ‘Saxa’ with 2C = 1.11 pg [10] and GC = 38.6% [11] were gently supplied by Jaroslav Doležel (Experimental Institute of Botany, Czech Republic). Seeds were germinated at 30 °C and plantlets were grown in a greenhouse at 25 °C.

Isolation of nuclei

Nuclei were extracted from young leaves of J. curcas (sample) and R. sativus (standard) according to Galbraith [12]

Flow cytometry

The fluorescence peaks of G0/G1 nuclei of J. curcas stained by PI, DAPI and CMA3 showed CVs varying between 3.8 and 4.6% (Fig. 1). Since the fluorescence peaks of G0/G1 nuclei from R. sativus (standard) were tuned to channel 100, we calculated the average GC level to be 38.7% ± 1.563, AT = 61.3% ± 0.159, and the mean 2C value equal to 0.85 pg ± 0.006, i.e. C = 0.416 × 109 bp (Fig. 1, Table 1).

The GC level that we calculated for the J. curcas genome is about the same as that found for Arabidopsis and is

Discussion

The low average value of CV associated to the fluorescence peaks of G0/G1 nuclei of this study indicates that the critical number of intact nuclei was reached during the extraction procedure with OTTO I and II buffers [13]. Distributions of fluorescence with high resolution and low CVs were also found by Doležel and Bartoš [31] and Loureiro et al. [14] using the OTTO I buffer. This buffer contains citric acid that may help to maintain the nucleus integrity.

The data also indicate that the genome

Acknowledgements

We thank Paulo Carvalho and Emilia Bolin for proofreading the manuscript. We thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Fundação Oswaldo Cruz (FIOCRUZ) for providing a research fellowship from the Centro de Desenvolvimento Tecnológico em Saúde (CDTS) to N. Carels. This work was financially supported by a grant from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil (no. 471214/2006-0).

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