A cost-effective oligo-based barcode system for chromosome identification in longan and lychee

Oligonucleotide (Oligo)-based fluorescence <i>in situ</i> hybridization (FISH) represents a highly effective methodology for identifying plant chromosomes. Longan is a commercially significant fruit species, yet lacking basic chromosomal markers has hindered its cytogenetic research. In this study, we developed a cost-effective oligo-based system for distinguishing chromosomes of longan (<i>Dimocarpus longan</i> Lour., 2<i>n</i> = 2<i>x</i> = 30). For this system, each synthesized oligo contained two chromosome-specific sequences that spanned a distance of over 200 kb, and a PCR-based flexible amplification method coupled with nested primers was used for probe labeling. The use of these oligo-based barcodes enabled the marking of 36 chromosomal regions, which allowed for the unambiguous distinction of all 15 chromosomes in both longan and lychee (<i>Litchi chinensis</i> Sonn., 2<i>n</i> = 2<i>x</i> = 30) species. Based on the identification of individual chromosomes, we constructed karyotypes and detected genome assembly errors involving the 35S ribosomal RNA gene (35S rDNA) in longan and lychee. Developing oligo-based barcodes offers considerable promise for advancing cytogenetic research in longan, lychee, and their related species. Furthermore, this cost-effective synthesis system can be referred to the development of new oligo libraries among other species.