Abstract
Plant cell proliferation is regulated by nutrient availability, and expression of cyclin D is regulated by sugars by hexokinase-dependent pathway. Nucleolin is a global regulator of ribosome synthesis and its expression in yeast and animals is linked with cell proliferation. A large fraction of Arabidopsis mRNAs that increased significantly within 6 hr-treatment with sucrose was occupied by genes in "protein synthesis" including a gene for nucleolin (AtNucl.-1) and about 200 genes for ribosomal proteins (RPs). Glucose, but not 2-deoxyglucose, also caused increase in mRNAs of these genes, suggesting the hexokinase sensor-independent manner of regulation. A disruptant of AtNucl.-1 contained significantly higher levels of pre-rRNA sequences that are removed during processing, and showed phenotypes such as decreased growth, narrow leaves and increased number of stems. In addition, sugar-induced changes in mRNAs for RPs were lost in the disruptant, suggesting the involvement of AtNucl.-1 in the regulation of expression of RPs.
