AUTHOR=Kim Joo Yong , Kwon Ye Jin , Kim Sung-Il , Kim Do Youn , Song Jong Tae , Seo Hak Soo 

TITLE=Ammonium Inhibits Chromomethylase 3-Mediated Methylation of the Arabidopsis Nitrate Reductase Gene NIA2

JOURNAL=Frontiers in Plant Science

VOLUME=6

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.01161

DOI=10.3389/fpls.2015.01161

ISSN=1664-462X

ABSTRACT=<p>Gene methylation is an important mechanism regulating gene expression and genome stability. Our previous work showed that methylation of the nitrate reductase (NR) gene <italic>NIA2</italic> was dependent on chromomethylase 3 (CMT3). Here, we show that CMT3-mediated <italic>NIA2</italic> methylation is regulated by ammonium in <italic>Arabidopsis thaliana</italic>. CHG sequences (where H can be A, T, or C) were methylated in <italic>NIA2</italic> but not in <italic>NIA1</italic>, and ammonium [(NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>] treatment completely blocked CHG methylation in <italic>NIA2</italic>. By contrast, ammonium had no effect on <italic>CMT3</italic> methylation, indicating that ammonium negatively regulates CMT3-mediated <italic>NIA2</italic> methylation without affecting <italic>CMT3</italic> methylation. Ammonium upregulated <italic>NIA2</italic> mRNA expression, which was consistent with the repression of <italic>NIA2</italic> methylation by ammonium. Ammonium treatment also reduced the overall genome methylation level of wild-type <italic>Arabidopsis</italic>. Moreover, CMT3 bound to specific promoter and intragenic regions of <italic>NIA2</italic>. These combined results indicate that ammonium inhibits CMT3-mediated methylation of <italic>NIA2</italic> and that of other target genes, and CMT3 selectively binds to target DNA sequences for methylation.</p>