The Expression Pattern of the Gene for NPK1 Protein Kinase Related to Mitogen-Activated Protein Kinase Kinase Kinase (MAPKKK) in a Tobacco Plant: Correlation with Cell Proliferation

Abstract

Mitogen-activated protein kinase (MAPK) cascades consist of members of three families of protein kinases: the MAPK family, the MAPK kinase family, and the MAPK kinase kinase (MAPKKK) family. Some of these cascades have been shown to play central roles in the transmission of signals that control various cellular processes including cell proliferation. Protein kinase NPK1 is a structural and functional tobacco homologue of MAPKKK, but its physiological function is yet unknown. In the present study, we have investigated sites of expression of the NPK1 gene in a tobacco plant and developmental and physiological controls of this expression. After germination, expression of NPK1 was first detected in tips of a radicle and cotyledons, then in shoot and root apical meristems, surrounding tissues of the apical meristems, primordia of lateral roots, and young developing organs. No expression was, however, observed in mature organs. Incubation of discs from mature leaves of tobacco with both auxin and cytokinin induced NPK1 expression before the division of cells. It was also induced at early stages of the development of primordia of lateral roots and adventitious roots. Thus, NPK1 expression appears to be tightly correlated with cell division or division competence. Even when an inhibitor of DNA synthesis was added during the germination or the induction of lateral roots by auxin, NPK1 expression was detected. These results showed that the NPK1 expression precedes DNA replication. We propose that NPK1 participates in a process involving the division of plant cells.

The NPK1 mitogen-activated protein kinase kinase kinase is a regulator of cell-plate formation in plant cytokinesis

“…Tobacco plants, Nicotiana tabacum SR1, were grown on Murashige and Skoog medium plates at 26°C under cycles of 16 h of light and 8 h of dark (Nakashima et al 1998). Transgenic BY-2 cells and tobacco plants were generated by Agrobacterium-mediated transformation (Onouchi et al 1995;Nakashima et al 1998), in which LBA4404 strain was used.…”

“…NPK1 and its Arabidopsis orthologous genes, ANP1/2/3, are transcribed in proliferating and division-competent cells or in organs rich in these cells, an observation that suggests their role in cell division (Banno et al 1993;Nishihama et al 1997;Nakashima et al 1998). Recently, it was reported that overexpression of the kinase domain of NPK1 or ANP1 in maize or Arabidopsis cells results in suppression of auxin-induced gene expression and in activation of stress signaling (Kovtun et al 1998(Kovtun et al , 2000.…”

An Arabidopsis Mitogen-Activated Protein Kinase Kinase Kinase Gene Family Encodes Essential Positive Regulators of Cytokinesis

“…The Arabidopsis ANP genes were isolated originally as a result of their homology with the tobacco NPK1 gene (Banno et al, 1993;Nishihama et al, 1997;Machida et al, 1998;Nakashima et al, 1998). Work by Nishihama et al (2001) has demonstrated that the NPK1 gene is involved in the regulation of cytokinesis in tobacco.…”

The Arabidopsis NUCLEUS- AND PHRAGMOPLAST-LOCALIZED KINASE1-Related Protein Kinases Are Required for Elicitor-Induced Oxidative Burst and Immunity

“…NPK1 regulates cytokinesis (Nakashima et al, 1998) as well as the effector-triggered immunity and development in Nicotiana benthamiana (Jin et al, 2002). ANPs have also been reported to be involved in the inhibition of auxin-induced gene expression.…”