Possible existence of a system similar to bacterial restriction–modification in plants

Abstract

The bacterial restriction–modification (R-M) system has evolved as a defense mechanism against infectious phages and other types of integration of foreign DNA fragments into the host chromosome through recombination. In this study, we identified two endonucleases (wheat endonuclease 1-WEN1 and wheat endonuclease 2-WEN2) and the adenine-DNA methyltransferase WAD (involved in mitochondrial DNA methylation) in the vesicular fraction of coleoptiles of wheat Triticum aestivum. WEN1 and WEN2 have multidirectional sensitivity to DNA methylation and to the presence of S-adenosyl-L-methionine and Ca2+ ions, which suggests their participation in the protection of mitochondrial DNA, similar to bacterial DNA. WEN2 has a GAT recognition site, which is part of the methylation site of adenine DNA methyltransferase (WAD-TGATCA) and hydrolyzes the CG (GC) bond upstream of the recognition site only if it is not methylated. Based on the interrelations between the two enzymes, we propose that an R-M system similar to that of the type IV observed in bacteria may exist in plants.