Evolutionary conservation and multilevel post-translational control of S-adenosyl-homocysteine-Hydrolase in land plants

Trans-methylation reactions are intrinsic to cellular metabolism in all living organisms. In land plants, a range of substrate-specific methyltransferases catalyze the methylation of DNA, RNA, proteins, cell wall components and numerous species-specific metabolites, thereby providing means for growth and acclimation in various terrestrial habitats. Trans-methylation reactions consume vast amounts of S-adenosyl-L-methionine (SAM) as a methyl donor in several cellular compartments. The inhibitory reaction by-product, S-adenosyl-L-homocysteine (SAH), is continuously removed by SAH hydrolase (SAHH) activity, and in doing so essentially maintains trans-methylation reactions in all living cells. Here we report on the evolutionary conservation and multilevel post-translational control of SAHH in land plants. We find that SAHH forms oligomeric protein complexes in phylogenetically divergent land plants, and provide evidence that the predominant enzyme is a tetramer. By analyzing light-stress-induced adjustments occurring on SAHH in Arabidopsis thaliana and Physcomitrella patens, we demonstrate that both angiosperms and bryophytes undergo regulatory adjustments in the levels of protein complex formation and post-translational modification of this metabolically central enzyme. Collectively, these data suggest that plant adaptation to terrestrial environments involved evolution of regulatory mechanisms that adjust the trans-methylation machinery in response to environmental cues.