MOLECULAR STABILITY ASSESSMENTS OF TREES REGENERATED FROM CRYOPRESERVED MAHOGANY (<em>SWIETENIA</em> <em>MACROPHYLLA</em>) SEED GERMPLASM USING NON-RADIOACTIVE TECHNIQUES TO EXAMINE THE CHROMATIN STRUCTURE AND DNA METHYLATION STATUS OF THE RIBOSOMAL RNA GENES

Abstract

The cryopreservation technique employing desiccation-slow cooling procedure was applied for the in vitro conservation of mahogany (Swietenia macrophylla). An examination of DNA from trees regenerating from cryopreserved embryos showed identical Restriction Fragment Length Polymorphisms (RFLPs) after Hpa II/Msp I digestion in genomic DNA sequences and Hpa II ribosomal RNA gene (rDNA) sequences as compared to the DNA of non-cryopreserved mahogany trees. DNA-DNA hybridisation analysis showed that the CCGG target site in rDNA was preferentially methylated (CmCGG) in trees regenerated from cryopreserved germplasm. An examination of the DNA methylation status between the mother tree and the trees regenerated from cryopreservation showed little evidence to support a correlation between methylation
status and changes in chromatin structure. There were some differences in chromatin structure throughout the nuclear genome and within the rDNA sequence between the mother tree and the trees regenerated from cryopreserved embryos. While RFLP profiles signify genetic stability in mahogany trees derived from cryopreserved seed germplasm, the chromatin and DNA methylation changes may have significance for patterns of gene expression.