The rolA gene of Agrobacterium rhizogenes contains in
its untranslated leader region a
spliceosomal intron, which is spliced in Arabidopsis and in Nicotiana
tabacum. Expression under
the control of the 35S promoter from cauliflower mosaic virus of a rolA
gene derivative defective
in splicing still causes alterations of growth in transgenic tobacco plants.
Splicing of rolA mRNA is
required for efficient expression of the rolA phenotype in vivo.
Moreover, splicing is required for
efficient in vitro translation of the rolA mRNA. In contrast,
expression of a 35S-rolA gene
derivative with the ATG initiation codon replaced by ATA does not cause any
phenotypical
alteration. Mutations leading to amino acid substitutions at positions 37 and
40 of the rolA coding
region were isolated as null mutants in Arabidopsis plants transgenic
for the rolA gene. However,
when expressed in tobacco under the control of the 35S promoter, they cause a
rolA phenotype
reduced in the expressivity of its traits. The molecular characterization of
rolA mutants might be
useful for understanding the biochemical function of the rolA protein.