AUTHOR=Shinohara Naoki , Ohbayashi Iwai , Sugiyama Munetaka 

TITLE=Involvement of rRNA biosynthesis in the regulation of CUC1 gene expression and pre-meristematic cell mound formation during shoot regeneration

JOURNAL=Frontiers in Plant Science

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2014.00159

DOI=10.3389/fpls.2014.00159

ISSN=1664-462X

ABSTRACT=<p>At an early stage of shoot regeneration from calli of Arabidopsis, pre-meristematic cell mounds develop in association with localized strong expression of <italic>CUP-SHAPED COTYLEDON</italic> (<italic>CUC</italic>) genes. Previous characterization of <italic>root initiation-defective 3</italic> (<italic>rid3</italic>), an Arabidopsis mutant originally isolated as being temperature-sensitive for adventitious root formation, with respect to shoot regeneration implicated <italic>RID3</italic> in the negative regulation of <italic>CUC1</italic> expression and the restriction of cell division in pre-meristematic cell mounds. Positional cloning has identified <italic>RID3</italic> as a WD40 repeat protein gene whose molecular function was not investigated before. Here we performed <italic>in silico</italic> analysis of RID3 and found that RID3 is orthologous to IPI3, which mediates pre-rRNA processing in <italic>Saccharomyces cerevisiae</italic>. In the <italic>rid3</italic> mutant, rRNA precursors accumulated to a very high level in a temperature-dependent manner. This result indicates that RID3 is required for pre-rRNA processing as is IPI3. We compared <italic>rid3</italic> with <italic>rid2</italic>, a temperature-sensitive mutant that is mutated in a putative RNA methyltransferase gene and is impaired in pre-rRNA processing, for seedling morphology, shoot regeneration, and <italic>CUC1</italic> expression. The <italic>rid2</italic> and <italic>rid3</italic> seedlings shared various developmental alterations, such as a pointed-leaf phenotype, which is often observed in ribosome-related mutants. In tissue culture for the induction of shoot regeneration, both <italic>rid2</italic> and <italic>rid3</italic> mutations perturbed cell-mound formation and elevated <italic>CUC1</italic> expression. Together, our findings suggest that rRNA biosynthesis may be involved in the regulation of <italic>CUC1</italic> gene expression and pre-meristematic cell-mound formation during shoot regeneration.</p>