Finding directionality – The liverwort, Marchantia polymorpha, tells us an evolutionarily conserved mechanism of polarized cell growth in land plants

March 21(Wed), 2018

The research group of Hiroyasu Motose, Associate Professor, Kento Otani, aformer graduate student, and Taku Takahashi, Professor at the Department of Biological Science, Graduate School of Natural Science and Technology, Okayama University, together with collaborative research groups ofKobe University and Kyoto University, discovered a mechanism of polarized growth of plant cells,using a basal land plant (liverwort), Marchantia polymorpha.They also showed that this mechanism is conserved through the evolution of land plants and may have contributed to the formation of the early rooting system,rhizoids (Fig. 1, 2).

 

Currently, there exists a wide variety of land plants. These land plants are considered to have evolved from freshwater algae through bryophyte-like plants to their current stage. The early land plants have had no roots, rather they adhered to the ground using rhizoid cells and obtained water and nutrients from the soil in order to adapt to terrestrial environments, as in the modern bryophytes. The ventral epidermis of liverworts that is touching the ground underwent tip growth to develop into hair-like filamentous cells, rhizoids (Fig. 1, 2).  However, the mechanism of directional growth of rhizoid cells remained unclear.

The research group of Hiroyasu Motose and his colleagues used the liverwort, Marchantia polymorpha, which diverged in the early stage of the land plant evolution and still maintains its original properties. They revealed that the NIMA-related protein kinase 1 (MpNEK1) directs tip growth in rhizoids (Fig. 3-5). MpNEK1 localizes to the apical dome of rhizoids and maintains the growth directionality of rhizoids (Fig. 4-5). In the absence of MpNEK1, rhizoids grow to the various directions, resulting in the crooked morphology rather than the straight filaments (Fig. 3).

These findings provide a novel, universal understanding of how cells determine and maintain their growth direction. The NEK family of protein kinases are conserved in most eukaryotes, including humans and fungi. They control cell division, neuron morphogenesis, and cilia, and a lack of NEK function can induce various diseases (cancer and polycystic kidney disease). This research may provide an important hint for understanding physiological and molecular basis of such biological phenomena.

 

These findings were published in the leading primary research journal of developmental biology “Development” at 12:30 a.m., March 2, 2018, British time (9:30 a.m. in Japan).

Article Information

DOI: 10.1242/dev.154617
Authors: Kento Otani, Kimitsune Ishizaki, Ryuichi Nishihama, Shogo Takatani, Takayuki Kohchi, Taku Takahashi, Hiroyasu Motose
Journal: Development
Title: An evolutionarily conserved NIMA-related kinase directs rhizoid tip growth in the basal land plant Marchantia polymorpha
Year of Publication: 2018

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