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Plant Physiol. 2018 Nov 7. pii: pp.01150.2018. doi: 10.1104/pp.18.01150. [Epub ahead of print]

ANGUSTIFOLIA Regulates Actin Filament Alignment for Nuclear Positioning in Leaves.

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Konan Univeristy CITY: Kobe Japan [JP].
Kyoto University CITY: Kyoto Japan [JP].
University of Shizuoka CITY: Shizuoka POSTAL_CODE: 4228526 Japan [JP].
Nara Institute of Science and Technology CITY: Ikoma STATE: Na POSTAL_CODE: 630-0192 Japan [JP].
University of Tokyo CITY: Tokyo Japan [JP].
Univ. Tokyo CITY: Tokyo POSTAL_CODE: 113-0033 Japan [JP].
Konan University CITY: Kobe POSTAL_CODE: 606-8502 Japan [JP]


During dark adaptation, plant nuclei move centripetally toward the mid-plane of the leaf blade; thus the nuclei in 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 (Arabidopsis thaliana) leaves. Two mutants defective in the positioning of nuclei in the dark were isolated and designated as unusual nuclear positioning 1 (unp1) and unp2. In the dark, nuclei of unp1 were positioned at the anticlinal walls of adaxial and abaxial mesophyll cells and abaxial pavement cells, whereas the nuclei of unp2 were positioned at the anticlinal walls of mesophyll and pavement cells in both the adaxial and abaxial sides. unp1 was caused by a dominant-negative mutation in ACTIN7, and unp2 resulted from a recessive mutation in AN. Actin filaments in unp1 were fragmented and reduced in number, which led to pleiotropic defects in nuclear morphology, cytoplasmic streaming, and plant growth. The mutation in AN caused aberrant positioning of nuclei-associated actin filaments at the anticlinal walls. AN was detected in the cytosol, where it physically interacted with plant-specific dual-specificity tyrosine phosphorylation-regulated kinases (DYRKPs) and itself. The DYRK inhibitor (1Z)-1-(3-ethyl-5-hydroxy-2(3H)-benzothiazolylidene)-2-propanone (INDY) 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.

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