The ang3 mutation identified the ribosomal protein gene RPL5B with a role in cell expansion during organ growth

The role of translation in the regulation of higher plant growth and
development is not well understood. Mutational analysis is a powerful tool
to identify and study the function of genes related to a biological process,
such as growth. Here we analyzed functionally the angusta3 (ang3) narrow
leaf mutant. The ANG3 gene was cloned by fine mapping combined with
candidate gene sequencing and it corresponded to the ribosomal protein gene
RPL5B. Based on amino acid sequence homology, promoter DNA sequence
homology and in silico gene expression analysis, RPL5B was found to be
putatively functionally redundant with RPL5A. The morphological analysis of
ang3 mutants showed that the leaf lamina area was significantly reduced from
the third rosette leaf on, mainly because of decreased width. Cellular analysis
of the abaxial epidermal cell layer of the third leaf indicated that the cell
number in the mutant was similar to that of the wild type, but the cell size was
significantly reduced. We postulate that the reduced cell expansion in the
epidermis contributes to the narrow shape of ang3 leaves. Growth was also
significantly impaired in hypocotyls and primary roots, hinting at a general
role for RPL5B in organ growth, unrelated to dorsiventral axis formation.
Comparison of the transcriptome of the shoot apices of the mutant and the
wild type revealed a limited number of differentially expressed genes, such
as MYB23 and MYB5, of which the lower expression in the ang3 mutant
correlated with reduced trichome density. Our data suggest that translation is
an important level of control of growth and development in plants.