Conditional effects of the epigenetic regulator JUMONJI 14 in <i>Arabidopsis</i> root growth

Abstract

Methylation of lysine 4 in histone 3 (H3K4) is a post-translational modification that promotes gene expression. H3K4 methylation can be reversed by specific demethylases with an enzymatic Jumonji C domain. In <i>Arabidopsis thaliana</i>, H3K4-specific JUMONJI (JMJ) proteins distinguish themselves by the association with an F/Y-rich (FYR) domain. Here, we report that <i>jmj14</i> mutations partially suppress reduced root meristem size and growth vigor of <i>brevis radix</i> (<i>brx</i>) mutants. Similar to its close homologs, <i>JMJ15</i>, <i>JMJ16</i> and <i>JMJ18</i>, the <i>JMJ14</i> promoter confers expression in mature root vasculature. Yet, unlike <i>jmj14</i>, neither <i>jmj16</i> nor <i>jmj18</i> mutation markedly suppresses <i>brx</i> phenotypes. Domain-swapping experiments suggest that the specificity of JMJ14 function resides in the FYR domain. Despite <i>JMJ14</i> promoter activity in the mature vasculature, <i>jmj14</i> mutation affects root meristem size. However, JMJ14 protein is observed throughout the meristem, suggesting that the <i>JMJ14</i> transcript region contributes substantially to the spatial aspect of <i>JMJ14</i> expression. In summary, our data reveal a role for JMJ14 in root growth in sensitized genetic backgrounds that depends on its FYR domain and regulatory input from the <i>JMJ14</i> cistron.