Abstract
In yeast and animals, nucleolin functions as a global regulator of ribosome synthesis and their expression is tightly linked with cell proliferation. Between two Arabidopsis genes for nucleolin, expression of AtNucl.1 is inducible by sugars together with many genes for ribosomal proteins (RPs) and snoRNPs. Disruption of AtNucl.1 by T-DNA insertion caused not only reduced pre-rRNA processing but also reduced sugar-induced expression of RP genes. The AtNucl.1-disruptants grew poorly, yet lived longer, than the wild type and showed various phenotypes such as pointed leaves and short valve. Unlike AtNucl.1, expression of AtNucl.2 was hardly detected except in flower buds and AtNucl.2-disruptants grew normally. However, a genetic cross between AtNucl.1- and AtNucl.2-disruptants did not produce seeds homozygous for both mutations suggesting that double disruptants are lethal. Although nucleolin-null yeast mutants can grow even with severely reduced growth rate and increased cold-sensitivity, nucleolin seems to be essential for growth of Arabidopsis.
