Carpenter R et al. 1990
- Authors:
Carpenter R. Coen ES.
- Title:
Floral homeotic mutations produced by transposon-mutagenesis in
Antirrhinum majus.
- Reference location:
Genes & Development. 4(9):1483-93, 1990 Sep.
- Abstract:
To isolate and study genes controlling floral development, we have carried
out a large-scale transposon-mutagenesis experiment in Antirrhinum majus.
Ten independent floral homeotic mutations were obtained that could be
divided into three classes, depending on whether they affect (1) the
identity of organs within the same whorl; (2) the identity and sometimes
also the number of whorls; and (3) the fate of the axillary meristem that
normally gives rise to the flower. The classes of floral phenotypes
suggest a model for the genetic control of primordium fate in which class
2 genes are proposed to act in overlapping pairs of adjacent whorls so
that their combinations at different positions along the radius of the
flower can specify the fate and number of whorls. These could interact
with class 1 genes, which vary in their action along the vertical axis of
the flower to generate bilateral symmetry. Both of these classes may be
ultimately regulated by class 3 genes required for flower initiation. The
similarity between some of the homeotic phenotypes with those of other
species suggests that the mechanisms controlling whorl identity and number
have been highly conserved in plant evolution. Many of the mutations
obtained show somatic and germinal instability characteristic of
transposon insertions, allowing the cell-autonomy of floral homeotic genes
to be tested for the first time. In addition, we show that the deficiens
(def) gene (class 2) acts throughout organ development, but its action may
be different at various developmental stages, accounting for the
intermediate phenotypes conferred by certain def alleles. Expression of
def early in development is not necessary for its later expression,
indicating that other genes act throughout the development of specific
organs to maintain def expression. Direct evidence that the mutations
obtained were caused by transposons came from molecular analysis of leaf
or flower pigmentation mutants, indicating that isolation of the homeotic
genes should now be possible.
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