Actin represses stem cell maintenance in Arabidopsis under drought stress

Stem cells endow plant with the ability to grow continuously, and also provide plasticity for plant growth and development under adverse environmental conditions. WUSCHEL (WUS) and WUSCHEL-RELATED HOMEOBOX (WOX) family proteins play crucial roles in stem cell maintenance of Arabidopsis. Drought is one of the abiotic stresses that severely repress the growth of plant. However, the response of plant stem cell to drought stress remains unclear. Actin (ACT), the main component of the microfilament cytoskeleton, is also involved in plant cell responses to various abiotic stresses. In this study, we investigated the involvement of vegetative actins in stem cell maintenance of Arabidopsis under drought stress. The mutation of ACT7, rather than ACT8, enhances the drought tolerance of Arabidopsis. Specifically, drought stress and osmotic stress increase the expression of ACT7, but repress the expression of WUS/WOX genes in wild-type plants. However, the expression levels of WUS/WOX in the act7 mutant were higher than those in wild-type plants under drought stress and osmotic stress. Consistently, the overexpression of ACT7 represses WUS/WOX expression and the growth of Arabidopsis under normal growth condition. These results suggested that ACT7 can repress the expression of WUS/WOX genes under drought stress and osmotic stress. Furthermore, our results revealed that ACT7 interact with WUS/WOX protein to bind to the WUS/WOX promoter, thereby further inhibiting the expression of WUS/WOX genes. In summary, ACT7 represses stem cell maintenance of Arabidopsis under drought stress by inhibiting the expression of WUS/WOX genes.