Gene Cloning and Characterization - Genetics, Genomics and Breeding of Crop Plants - page 192

5'-GCCMAYACMGGCCATCTRCTAGC-3' (reverse). First strand cDNA was
made with total RNA using a Superscript preamplification kit. The cDNA
was amplified with P-A and P-B primers. The PCR product of 750 bp was
cloned into the pCRII vector. The RACE approach was used to isolate the
5'- and 3'-ends of the Psy cDNA. The 1,598 bp long reconstructed full-length
cDNA sequence (GenBank accession number AJ304825) contained 1,242 bp
coding sequence, 172 nucleotides of 5'-untranslated region (UTR), and 170
nucleotides of 3'-UTR (Salvini et al. 2005). The predicted protein (46.8 kDa)
displayed a sequence of 414 amino acid residues with a putative transit
sequence for plastid targeting in the N-terminal region. The program CloroP
1.1 (Emanuelsson et al. 1999) predicts a transit peptide cleavage site between
residue 67 and 68. Organspecific expression of HaPsy was analyzed by
relative RT-PCR assays (Salvini et al. 2005). The expression of HaPsy is very
high in cotyledons, and young and mature leaves, but lower in stem and
nearly absent in roots. HaPsy is regulated during leaf development. The role
of the phytoene synthase gene HaPSy in controlling carotenoid biosynthesis
is demonstrated by the concurrent increase of HaPsy transcript levels with
the light-dependent, enhanced carotenoid production in green tissues of
sunflower (Salvini et al. 2005).
A homeobox (HD)-containing cDNA was isolated by Valle et al. (1997).
As template for PCR, a cDNA library prepared from H. annuus root mRNA
and cloned in lambda gt10 was used. A degenerate oligonucleotide derived
from the conserved peptide sequence WFQNRRA from helix 3 of the HD
and an oligonucleotide containing the sequence flanking the cloning site of
lambda gt10 were used as the primers. The corresponding gene was named
Hahr1 ( Helianthus annuus homeobox from roots) that encodes a 682 aa protein
with a M r 76,677. Hahr1 expression was primarily found in dry seeds,
hypocotyls and roots at stages associated with early developmental events
(Valle et al. 1997).

6.3.2.2 Non-dormancy

Seed dormancy and germination are regulated by a wide range of plant
hormones, including abscisic acid (ABA), ethylene, gibberellin (GA), and
brassinosteroids, of which ABA is the primary mediator of seed dormancy
(Koorneef et al. 2002). Major enzymes of the carotenoid biosynthesis pathway
like phytoene desaturase, ζ-carotene desaturase, carotenoid isomerase and
lycopene -cyclase, are also essential for the biosynthesis of carotenoid

precursors of ABA. Impairment of carotenoid biosynthesis causes photo-
oxidation and ABA-deficient phenotypes in rice, of which the latter is a
major factor controlling the pre-harvest sprouting (PHS) or vivipary trait
(Fang et al 2008). In addition, the ratio of ABA/GA is distinctly reduced in
phs4-1 mutant seeds in rice. The increased GA might result from a reduced