SUPERWOMAN1 and DROOPING LEAF genes control floral organ identity in rice.
2003
We analyzed recessive mutants of two homeotic genes in rice,
SUPERWOMAN1 ( SPW1 ) and DROOPING LEAF ( DL ).
The homeotic mutation spw1 transforms stamens and lodicules into
carpels and palea-like organs, respectively. Two spw1 alleles,
spw1-1 and spw1-2 , show the same floral phenotype and did
not affect vegetative development. We show that SPW1 is a rice
APETALA3 homolog, OsMADS16 . In contrast, two strong alleles
of the dl locus, drooping leaf-superman1 ( dl-sup1 )
and drooping leaf-superman2 ( dl-sup2 ), cause the complete
transformation of the gynoecium into stamens. In these strong mutants, many
ectopic stamens are formed in the region where the gynoecium is produced in
the wild-type flower and they are arranged in a non-whorled, alternate
pattern. The intermediate allele dl-1 ( T65 ), results in an
increase in the number of stamens and stigmas, and carpels occasionally show
staminoid characteristics. In the weakest mutant, dl-2 , most of the
flowers are normal. All four dl alleles cause midrib-less drooping
leaves. The flower of the double mutant, spw1 dl-sup , produces
incompletely differentiated organs indefinitely after palea-like organs are
produced in the position where lodicules are formed in the wild-type flower.
These incompletely differentiated organs are neither stamens nor carpels, but
have partial floral identity. Based on genetic and molecular results, we
postulate a model of stamen and carpel specification in rice, with DL
as a novel gene controlling carpel identity and acting mutually and
antagonistically to the class B gene, SPW1 .
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