Adaptive methylation pattern of ribosomal DNA in wild barler from Israel

Abstract

Forty four accessions of wild barley, H. spontaneum were assayed to study the methylation status of ribosomal DNA repeat units. For this purpose, BamHI and HpaII, which are, methylation sensitive restriction enzymes and MspI, which is methyl insensitive enzyme, were used for restriction digestion. Southern blots were hybridized with pTa71 probe, which represented a complete ribosomal DNA repeat unit from bread wheat. Wild barley material studied belonged to two ecologically diverse climatic and edaphic microsites (the "Evolution Canyon" at Lower Nahal Oren, Mount Carmel, and Tabigha, Eastern Upper Galilee Mountains), from Israel, each having two different ecogeographcally contrasting microniches. HpaII did not cleave ribosomal DNA, while MspI gave a pattern typical of ribosomal DNA. In contrast, a total of 23 BamHI phenotypes were observed due to methylation. Same rDNA repeat length units exhibited different methylation status at different microsites and miocroniches, as inferred from RFLPs observed. Differential methylation status of same rDNA repeat unit seems to be associated with ecological conditions dominating at a particular microsite or microniche suggesting a role of natural selection in determining methylation patterns.