Because of omission of the second meiotic division,
Arabidopsis osd1 produces diploid male and female
gametes and its self-fertilization generates tetraploid
progeny. To address the function of Os02g37850, we
used flow cytometry to determine the ploidy of the progeny that are homozygous for the AMBA12, AMQF10
and ALJA10 mutations. This revealed the presence of
100% (n = 82), 37% (n = 27) and 5% (n = 20) of tetraploid plants in the respective progeny, the rest being
diploid. This suggests that mutations of Os02g37850
can provoke the production of male and female diploid
gametes. AMBA12 appears to be a null mutant, while
AMQF10 and ALJA10 appear partially affected. Consistently, RT-PCR experiments showed that the OSD1
spliced mRNA is barely detectable in AMBA12 homozygotes, and is only reduced in abundance in AMQF10
(Supplementary information, Figure S3). We then compared meiosis in wild type and AMBA12. First, observation of male meiotic products revealed the presence
of 100% dyads (n = 500) in AMBA12 homozygotes,
instead of tetrads in wild type (Figure 3), showing that a
single meiotic division occurs in AMBA12. In AMQF10,
a mixture of dyads (29%) and tetrads were observed (n =
130), in accordance with the mixed ploidy in offspring of
this mutant. Chromosome spreads showed that the first
meiotic division in AMBA12 was indistinguishable from
wild type (Figure 4), suggesting that crossover formation
and homologous chromosome segregation were unaffected, but no second division took place. Thus, a single
first meiotic division occurred in AMBA12. In summary,
disruption of Os02g37850 recapitulated the Arabidopsis
osd1 meiotic defect: the omission of the second meiotic
division which leads to the production of functional diploid gametes. We therefore named Os02g37850 OsOSD1
and AMBA12 Ososd1-1.