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the other hand, MYB21 transcripts were still detectable in myb21-t1 although
its level was greatly reduced in the mutant, suggesting that myb21-t1 is likely a
leaky allele (Figure 3B). After two rounds of backcross, we found that myb24-t1
and myb57-t1 mutant plants were phenotypically indistinguishable from the WT
control plant (Figure 3C; Table 2). However, in myb21-t1 the early developed
flowers (~the first 10 flowers) bore short stamens with greatly reduced fertility and
only the late developed flowers yielded proper seed settings (Figure 3C; Table 2).
A close look at the matured early flowers in myb21-t1 showed that the stamens
did produce pollens (Figure 3D, panel d). Cross-pollinating the pollens onto the
myb21-t1 stigma yielded seeds that were homozygous for myb21-t1 and onto the
WT stigma yielded myb21-t1 heterozygous seeds (data not shown), demonstrat-
ing that the short stamen is responsible for the partial sterile phenotype. Although
myb21-t1 is likely a leaky allele, the short stamen phenotype conferred by the
myb21-t1 mutation is identical to a MYB21 null allele we obtained later from
Gabi-Kat stock (stock number N311167, data not shown).
Figure 3.
MYB21, MYB24, and MYB57 Function Redundantly in Regulating the Stamen Filament
Development.
(A) Schematic
diagram shows the respective T-DNA insertions in the three MYB genes. Black box: exon; black
line: intron; triangle: T-DNA insertion site. (B) RT-PCR analysis of MYB24 transcripts in myb24-t1 and
MYB57 transcripts in myb57-t1 and northern analysis of MYB21 transcripts in myb21-t1. Total RNA for RT-
PCR and northern analysis was extracted from the young flower buds. (C) Comparison of main shoots bearing
siliques among different mutant lines as indicated. (D) Comparison of the stamen phenotype among different
mutant lines as indicated. Genotypes for flowers a-h in (D) corresponds to that showed in (C).
