Genome composition and pollen viability of Jatropha (Euphorbiaceae) interspecific hybrids by Genomic In Situ Hybridization (GISH)

Differential amplification of the subtelomeric satellite DNA JcSAT1 in the genus Jatropha L. (Euphorbiaceae)

Satellite DNAs (satDNAs) are highly repetitive sequences that occur in virtually all eukaryotic genomes and can undergo rapid copy number and nucleotide sequence variation among relatives. After chromosomal mapping of the satDNA JcSAT1, it was found a large accumulation at subtelomeres of Jatropha curcas (subgenus Curcas), but an absence of these monomers in J. integerrima (subgenus Jatropha). This fact suggests a dynamic scenario for this satellite repeat in Jatropha genomes. Here, we used a multitasking approach (sequence analysis, DNA blotting and chromosomal mapping) to investigate the molecular organization and chromosomal abundance and distribution of JcSAT1 in a broader group of species from the subgenus Jatropha (J. gossypiifolia, J. mollissima, J. podagrica, and J. multifida) in addition to J. curcas, with the aiming of understanding the evolution of this satDNA. Based on the analysis of BAC clone sequences of J. curcas, a large array (~ 30 kb) of 80 homogeneous monomers of JcSAT1 was identified in BAC 23J11. The monomer size was conserved (~ 358 bp) and contained a telomeric motif at the 5' end. PCR amplification coupled with a Southern blot revealed the presence of JcSAT1-like sequences in all species examined. However, a large set of genome copies was identified only in J. curcas, where a ladder-like pattern with multimers of different sizes was observed. In situ hybridization of BAC 23J11 confirmed the subtelomeric pattern for J. curcas, but showed no signals on chromosomes of species from the subgenus Jatropha. Our data indicate that JcSAT1 is a highly homogeneous satDNA that originated from a region near the telomeres and spread throughout the chromosomal subtermini, possibly due to frequent ectopic recombination between these regions. The abundance of JcSAT1 in the genome of J. curcas suggests that an amplification event occurred either at the base of the subgenus Curcas or at least in this species, although the repeat is shared by all species of the genus studied so far.