The Suppression of WRKY44 by GIGANTEA-miR172 Pathway Is Involved in Drought Response of <i>Arabidopsis thaliana</i>

<div><p>Water availability is an important environmental factor that controls flowering time. Many plants accelerate flowering under drought conditions, a phenomenon called drought escape. Four pathways are involved in controlling flowering time, but which ones participate in drought escape is not yet known. In this study, plants with loss-of-function mutations of <i>GIGANTEA (GI</i>) and <i>CONSTANS</i> (CO) exhibited abnormal drought-escape phenotypes. The peak mRNA levels of <i>GI</i> and FKF1 (Flavin-binding Kelch domain F box protein 1) and the mRNA levels of <i>CO</i> and FT (Flowering locus T) changed under drought stress. The microRNA factor <i>miRNA172E</i> was up-regulated by drought stress, and its up-regulation was dependent on <i>GI</i>, while other <i>miRNA172s</i> were not. Water-loss analyses indicated that <i>gi</i> mutants were more sensitive while <i>miRNA172</i> over-expressing (<i>miRNA</i>172-OX) plants were less so to drought stress than wild-type plants. Digital gene expression and real-time PCR analyses showed that <i>WRKY44</i> was down-regulated by <i>GI</i> and <i>miRNA172</i>. The WRKY44 protein could interact with TOE1 (a target of <i>miRNA</i>172) in a yeast two-hybrid system. We proposed that <i>GI–miRNA172–WRKY44</i> may regulate drought escape and drought tolerance by affecting sugar signaling in <i>Arabidopsis</i>.</p>