Expansion of the Cell Plate in Plant Cytokinesis Requires a Kinesin-like Protein/MAPKKK Complex

Abstract

The tobacco mitogen-activated protein kinase kinase kinase NPK1 regulates lateral expansion of the cell plate at cytokinesis. Here, we show that the kinesin-like proteins NACK1 and NACK2 act as activators of NPK1. Biochemical analysis suggests that direct binding of NACK1 to NPK1 stimulates kinase activity. NACK1 is accumulated specifically in M phase and colocalized with NPK1 at the phragmoplast equator. Overexpression of a truncated NACK1 protein that lacks the motor domain disrupts NPK1 concentration at the phragmoplast equator and cell plate formation. Incomplete cytokinesis is also observed when expression of NACK1 and NACK2 is repressed by virus-induced gene silencing and in embryonic cells from Arabidopsis mutants in which a NACK1 ortholog is disrupted. Thus, we conclude that expansion of the cell plate requires NACK1/2 to regulate the activity and localization of NPK1.

Mitosis-specific kinesins in Arabidopsis

“…The kinesin NACK1 of tobacco (Nicotiana tabacum) contains two MSA sequences in the promoter region that are responsible for mitosisdependent expression [11]. Accordingly, the NACK1 protein accumulates during M-phase, which is consistent with its function in cell plate expansion [12]. The MSA element is absent in the immediate upstream region of kinesins At4g21270, At4g05190 and At5g27550, suggesting that either the MSA sequence has degenerated beyond computer-assisted recognition or another mitosisspecific element exists for the expression of these particular kinesins.…”

“…For several plant kinesins, protein levels have been investigated throughout the cell cycle in synchronized Bright Yellow-2 (BY-2) cells [12,[29][30][31]. The protein levels …”

“…NACK1 (also named HIK [77]) and NACK2 (also named STUD [78] or TES [79]) play a role in phragmoplast MT dynamics [80]. NACK1 is essential for the completion of somatic cytokinesis and functions in the reorganization of MTs during the lateral expansion of the cell plate [12,77]; NACK2 is the closest homolog of NACK1 and takes part in the assembly of the radial MT array in male meiotic cytokinesis [78,79]. Both NACK1 and NACK2 interact with NPK1, a MAPKKK that controls phragmoplast expansion and cytokinesis [12].…”

“…NACK1 is essential for the completion of somatic cytokinesis and functions in the reorganization of MTs during the lateral expansion of the cell plate [12,77]; NACK2 is the closest homolog of NACK1 and takes part in the assembly of the radial MT array in male meiotic cytokinesis [78,79]. Both NACK1 and NACK2 interact with NPK1, a MAPKKK that controls phragmoplast expansion and cytokinesis [12]. Four mitotic up-regulated plant-specific kinesins that do not belong to the classic kinesin subfamilies are as yet uncharacterized (At3g44050, At3g17360, At3g20150 At5g23910; Table 2).…”

Structure, function, and evolution of plant NIMA-related kinases: implication for phosphorylation-dependent microtubule regulation

“…A series of studies using tobacco BY-2 (Nicotiana tabacum cv. Bright Yellow 2) cell line revealed that the MAP kinase cascade (NACK-PQR pathway) is required for phragmoplast expansion and for cell plate formation (Nishihama et al 2001;Nishihama et al 2002;Soyano et al 2003;Sasabe et al 2006). NACK kinesins activate the MAP kinase cascade, which consists of NPK1 mitogen-activated kinase kinase kinase (MAPKKK), NQK1 MAP kinase kinase (MAPKK), and NRK1 MAP kinase (MAPK).…”