Light Differentially Regulates Cell Division and the mRNA Abundance of Pea Nucleolin during De-Etiolation

Abstract

The abundance of plant nucleolin mRNA is regulated during de-etiolation by phytochrome. A close correlation between the mRNA abundance of nucleolin and mitosis has also been previously reported. These results raised the question of whether the effects of light on nucleolin mRNA expression were a consequence of light effects on mitosis. To test this we compared the kinetics of light-mediated increases in cell proliferation with that of light-mediated changes in the abundance of nucleolin mRNA using plumules of dark-grown pea (Pisum sativum) seedlings. These experiments show that S-phase increases 9 h after a red light pulse, followed by M-phase increases in the plumule leaves at 12 h post-irradiation, a time course consistent with separately measured kinetics of red light-induced increases in the expression of cell cycle-regulated genes. These increases in cell cycle-regulated genes are photoreversible, implying that the light-induced increases in cell proliferation are, like nucleolin mRNA expression, regulated via phytochrome. Red light stimulates increases in the mRNA for nucleolin at 6 h post-irradiation, prior to any cell proliferation changes and concurrent with the reported timing of phytochromemediated increases of rRNA abundance. After a green light pulse, nucleolin mRNA levels increase without increasing S-phase or M-phase. Studies in animals and yeast indicate that nucleolin plays a significant role in ribosome biosynthesis. Consistent with this function, pea nucleolin can rescue nucleolin deletion mutants of yeast that are defective in rRNA synthesis. Our data show that during de-etiolation, the increased expression of nucleolin mRNA is more directly regulated by light than by mitosis.

Arabidopsis Nucleolin Affects Plant Development and Patterning

“…Supporting this idea, alfalfa nucleolin is absent in stationary cells, but highly expressed before the onset of DNA replication at both the transcriptional and protein levels in logarithmically dividing cells (Bö gre et al, 1996). Furthermore, red light treatment induces pea nucleolin transcription 1 h prior to rRNA synthesis and coincides with increased cell division rates in pea apical internodes as well as increased nuclear number/ weight of pea plumules (Reichler et al, 2001). These data support a link between nucleolin and cell division in plants that may explain the growth defects and reduction in higher order venation characteristic of Arabidopsis parl1.…”

“…All transformed yeast were grown at For liquid growth complementation experiments, three samples each of both Dnsr1 mutant haploid strains containing either pEGH alone or pEGH containing the full-length Arabidopsis PARL1 cDNA, as well as three samples of the wild-type haploid strain transformed with pEGH alone were transferred from noninducing plates and grown in 5 mL noninducing media overnight. As described by Reichler et al (2001), equal amounts of each culture were then transferred to another 5 mL of noninducing media and grown to early log phase. Equal amounts of these cultures were then transferred to inducing media and grown to saturation while growth rate was monitored hourly by OD 600 readings.…”

“…However, nucleolin has been shown to be light regulated and to have DNA helicase and ATPase activity in pea (Pisum sativum; Tong et al, 1997;Reichler et al, 2001;Nasirudin et al, 2005), to be cell-cycle regulated in alfalfa (Medicago sativa;Bö gre et al, 1996), and to be part of a complex responsible for rRNA binding and in vitro pre-rRNA processing in Arabidopsis (Arabidopsis thaliana; Sáez-Vasquez et al, 2004). While the phenotypic consequences of mutations in nucleolin proteins have not been described, those of ribosomal proteins have been reported in Arabidopsis.…”

The nucleolar structure and the activity of NopA100, a nucleolin-like protein, during the cell cycle in proliferating plant cells

“…Apart from this, the expression of nucleolin is restricted to proliferating tissues of the plant (Bo¨gre et al 1996). In peas, the expression of nucleolin is regulated by light, following a close correlation with the effects of light in increasing cell proliferation and mitotic activity (Reichler et al 2001).…”

Light spectra affect the morphoanatomical and chemical features of clonal Phyllanthus tenellus Roxb. grown in vitro

“…Changes in morphogenesis by the effects of spectral green light showed that it is an important factor affecting plant development, contrary to some studies that reported green light to be innocuous to growth (Reichler et al, 2001). According to Folta and Maruhnich (2007), phytochromes and cryptochromes are responsible for the absorption of green light.…”