Telomeric localization of the Arabidopsis-type heptamer repeat, (TTTAGGG)n , at the chromosome ends in Saccharina japonica (Phaeophyta).

Abstract

Telomeres generally consist of short repeats of minisatellite DNA sequences and are useful in chromosome identification and karyotype analysis. To date, telomeres have not been characterized in the economically important brown seaweed Saccharina japonica, thus its full cytogenetic research and genetic breeding potential has not been realized. Herein, the tentative sequence of telomeres in S.japonica was identified by PCR amplification with primers designed based on the Arabidopsis-type telomere sequence (TTTAGGG)n , which was chosen out of three possible telomeric repeat DNA sequences typically present in plants and algae. After PCR optimization and cloning, sequence analysis of the amplified products from S.japonica genomic DNA showed that they were composed of repeat units, (TTTAGGG)n , in which the repeat number ranged from 15 to 63 (n=46). This type of repeat sequence was verified by a Southern blot assay with the Arabidopsis-type telomere sequence as a probe. The digestion of S.japonica genomic DNA with the exonuclease Bal31 illustrated that the target sequence corresponding to the Arabidopsis-type telomere sequence was susceptible to Bal31 digestion, suggesting that the repeat sequence was likely located at the outermost ends of the kelp chromosomes. Fluorescence insitu hybridizations with the aforementioned probe provided the initial cytogenetic evidence that the hybridization signals were principally localized at both ends of S.japonica chromosomes. This study indicates that the telomeric repeat of the kelp chromosomes is (TTTAGGG)n which differs from the previously reported (TTAGGG)n sequence in Ectocarpus siliculosus through genome sequencing, thereby suggesting distinct telomeres in brown seaweeds.