ANGUSTIFOLIA Regulates Actin Filament Alignment for Nuclear Positioning in Leaves

During dark adaptation, plant nuclei move centripetally toward the midplane of the leaf blade; thus, the nuclei on both the adaxial and abaxial sides become positioned at the inner periclinal walls of cells. This centripetal nuclear positioning implies that a characteristic cell polarity exists within a leaf, but little is known about the mechanism underlying this process. Here, we show that ANGUSTIFOLIA (AN) and ACTIN7 regulate centripetal nuclear positioning in Arabidopsis () leaves. Two mutants defective in the positioning of nuclei in the dark were isolated and designated as () and In the dark, nuclei of were positioned at the anticlinal walls of adaxial and abaxial mesophyll cells and abaxial pavement cells, whereas the nuclei of were positioned at the anticlinal walls of mesophyll and pavement cells on both the adaxial and abaxial sides. was caused by a dominant-negative mutation in , and resulted from a recessive mutation in Actin filaments in were fragmented and reduced in number, which led to pleiotropic defects in nuclear morphology, cytoplasmic streaming, and plant growth. The mutation in caused aberrant positioning of nuclei-associated actin filaments at the anticlinal walls. AN was detected in the cytosol, where it interacted physically with plant-specific dual-specificity tyrosine phosphorylation-regulated kinases (DYRKPs) and itself. The DYRK inhibitor (1)-1-(3-ethyl-5-hydroxy-2(3)-benzothiazolylidene)-2-propanone significantly inhibited dark-induced nuclear positioning. Collectively, these results suggest that the AN-DYRKP complex regulates the alignment of actin filaments during centripetal nuclear positioning in leaf cells.