Identification of TCP13 as an Upstream Regulator of ATHB12 during Leaf Development

Abstract

Leaves grow by distinct phases controlled by gene regulatory networks including many transcription factors. <i>Arabidopsis thaliana homeobox 12</i> (<i>ATHB12</i>) promotes leaf growth especially during the cell expansion phase. In this study, we identify TCP13, a member of the TCP transcription factor family, as an upstream inhibitor of <i>ATHB12</i>. Yeast one-hybrid screening using a 1.2-kb upstream region of <i>ATHB12</i> resulted in the isolation of TCP13 as well as other transcription factors. Transgenic plants constitutively expressing <i>TCP13</i> displays a significant reduction in leaf cell size especially during the cell expansion period, while repression of <i>TCP13</i> and its paralogs (<i>TCP5</i> and <i>TCP17</i>) result in enlarged leaf cells, indicating that TCP13 and its paralogs inhibit leaf development, mainly at the cell expansion phase. Its expression pattern during leaf expansion phase is opposite to <i>ATHB12</i> expression. Consistently, the expression of <i>ATHB12</i> and its downstream genes decreases when <i>TCP13</i> was overexpressed, and increases when the expression of <i>TCP13</i> and its paralogs is repressed. In chromatin immunoprecipitation assays using <i>TCP13-GFP</i> plants, a fragment of the <i>ATHB12</i> upstream region that contains the consensus sequence for TCP binding is strongly enriched. Taken together, these findings indicate that TCP13 and its paralogs inhibit leaf growth by repressing <i>ATHB12</i> expression.