Down-regulation of S-adenosyl-L: -homocysteine hydrolase reveals a role of cytokinin in promoting transmethylation reactions.
S-adenosyl-L: -homocysteine hydrolase (SAHH) is a key enzyme for maintenance of cellular transmethylation potential. Although a cytokinin-binding activity had been hypothesized for SAHH, the relation between cytokinin and transmethylation reactions has not been elucidated. Here we show that, of the two Arabidopsis thaliana SAHH genes, AtSAHH1 has a much higher expression level than AtSAHH2. A T-DNA insertion mutant of AtSAHH1 (sahh1-1) and the RNA interference (RNAi) plants (dsAtSAHH2) accumulated a higher level of cytokinins, exhibited phenotypic changes similar to those of cytokinin-overproducers, and their global DNA methylation status was reduced. On the other hand, cytokinins positively regulate the transmethylation pathway genes, including AtSAHH1, AtADK1 (for adenosine kinase), and this regulation involves the cytokinin activity. Furthermore, expression of three cytosine DNA methyltransferase genes examined was inducible by cytokinin treatment. Unlike adenine and adenosine which are SAHH inhibitors, the adenine-type cytokinins have no effect on SAHH activity at protein level. Changing of endogenous cytokinin levels by transgene expression resulted in alterations of DNA methylation status in the sahh1-1 background, suggesting that cytokinins promote DNA methylation, at least under transmethylation stringent conditions. These data demonstrate that the phytohormone cytokinin plays a role in promoting transmethylation reactions, including DNA methylation.
Li
Chun-Hong
CH
National Key Laboratory of Plant Molecular Genetics, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 200032, Shanghai, People's Republic of China.
Yu
Nan
N
Jiang
Shi-Min
SM
Shangguan
Xiao-Xia
XX
Wang
Ling-Jian
LJ
Chen
Xiao-Ya
XY
D000248:Adenosine Kinase / Q000235:genetics / Q000378:metabolism; D043383:Adenosylhomocysteinase / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003583:Cytokinins / Q000378:metabolism / Q000494:pharmacology* / Q000502:physiology; D019175:DNA Methylation / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D010937:Plant Growth Regulators / Q000378:metabolism / Q000494:pharmacology; D030821:Plants, Genetically Modified; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction
D029681:Arabidopsis Proteins; D003583:Cytokinins; D010937:Plant Growth Regulators; D000248:Adenosine Kinase; D043383:Adenosylhomocysteinase