Gene Cloning and Characterization - Genetics, Genomics and Breeding of Crop Plants - page 196

this can be uncoupled from its regulation during embryogenesis (Coca et al.
1996). Chimeric constructs containing the promoter and upstream sequences
of Ha hsp17.6 G1 in tobacco reproduced its unique seed-specific expression
previously reported in sunflower (Carranco et al. 1999). The expression of
sHSP genes is regulated mainly by cis -elements, described as heat shock
elements (HSEs) present in their promoters. The HSEs are arranged in
clusters of three or more inverted repeats of the sequence 5'-nGAAn-3', to
which, heat shock factors (HSFs) bind and control transcription (Carranco
et al. 1997; Nover et al. 2001).
6.3.3.2 Drought Related Genes
To identify genes regulated by water stress and abscisic acid in drought
tolerant sunflower transcript profiles of a drought tolerant and a drought
sensitive genotype were compared under field conditions (Ouvrard et al.
1996). By subtractive hybridization, six different cDNA clones (originally
designated sdi for s unflower d rought i nduced), corresponding to transcripts
accumulated in the leaves of the drought tolerant line during adaptive
response, were identified. Sequence analysis of the six cDNA clones revealed
homology to a non-specific lipid transfer protein (nsLTP), early light induced
proteins (ELIP), 1-aminocyclopropane-1-carboxylate oxidase (ACC oxidase)
and dehydrins (Ouvrard et al. 1996). Dehydrins are proteins produced
during late stages of plant embryo development and following any
environmental stimulus involving dehydration. Dehydrins represent an
immunologically distinct family of proteins, also known as Lea D11 subgroup
of late embryogenesis abundant (Lea) proteins (Dure et al. 1989), which
have been described in many plant species (Close 1997). The drought induced
genes identified in the drought tolerant sunflower line were named HaDhn1 ,
HaDhn2 and HaELip1 according to their homology to the dehydrin family
and to the early light induced protein (ELIP). In leaves of the drought tolerant
plants, the accumulation of HaDhn1 and HaDhn2 transcripts, but not HaELip1 ,
was correlated with the drought adaptive response (Cellier et al. 1998).
HaDhn2 transcription was upregulated in the tolerant genotype compared
to the sensitive after ABA treatment, whereas the transcript level of HaDhn1
was similar in tolerant and sensitive genotype. A sequence allelic to HaDhn1 ,
named HaDhn1a , was found to be expressed in the later stages of
embryogenesis in sunflower, depending on abscisic acid accumulation
(Giordani et al. 1999). Natali et al. (2003) investigated the variability of this
dehydrin encoding gene HaDhn1a in cultivated and wild sunflower
accessions. With respect to the overall sequence, variation in both the coding
and non-coding (intron and 3'-UTR) sequences was much larger among the
wild accessions than among cultivars. Inclusion of wild populations of H.
annuus into breeding programs might be a way to introduce a broader