We. Hable et al., VIVIPAROUS-5 ENCODES PHYTOENE DESATURASE, AN ENZYME ESSENTIAL FOR ABSCISIC-ACID (ABA) ACCUMULATION AND SEED DEVELOPMENT IN MAIZE, MGG. Molecular & general genetics, 257(2), 1998, pp. 167-176
The role of synthesis in the regulation of abscisic acid accumulation
was investigated in the developing maize seed. To do this, expression
and regulation of the abscisic acid biosynthetic enzyme phytoene desat
urase were examined. Comparison of the gene sequence encoding phytoene
desaturase and its transcript in the wild-type and viviparous-5 mutan
t showed that the mutant gene contains multiple insertions and deletio
ns, resulting in the synthesis of a larger transcript. In addition, th
e 55-kDa phytoene desaturase protein was not detectable in the vivipar
ous-5 mutant, indicating that this phenotype results from a mutation a
t the phytoene desaturase locus. Levels of phytoene desaturase transcr
ipt and protein were compared to abscisic acid levels during developme
nt to determine whether phytoene desaturase might regulate abscisic ac
id accumulation. In the endosperm, transcript levels were initially hi
gh and declined during late maturation and dormancy, while protein lev
els remained high throughout development. In the embryo, transcript le
vels were low and constant, while protein levels declined. Both tempor
al and tissue-specific expression of phytoene desaturase were unrelate
d to abscisic acid levels. An abscisic acid mutant (viviparous-2) defi
cient in phytoene desaturation was used to determine whether the wild-
type protein encoded by Viviparous-2 regulates phytoene desaturase. Ph
ytoene desaturase transcript and protein levels were compared in wild-
type and viviparous-2 mutant embryos and endosperm. Normalized levels
of phytoene desaturase were similar in wild-type and mutant tissues, s
uggesting that the wild-type Viviparous-2 protein does not regulate ph
ytoene desaturase transcript or protein levels.