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variability with regard to dehydrins into the cultivated sunflower. Giordani
et al. (2003) analyzed the PCR amplification products of the HaDhn1a gene
from 16 wild Helianthus species or subspecies on sequence level. All the
isolated sequences included the typical dehydrin domains (Y, S and K), a
portion of the 3'-UTR and an intron, inserted in the same position within
the S-domain-encoding region. Using these data for phylogenetic trees,
perennial and annual species formed a supported clade and H. annuus was
separated from this clade. Natali et al. (2007) observed light-induced
expression of HaDhn1 during de-etiolation of sunflower seedlings. However,
Western blot analyses suggest that transcription of the dehydrin gene is not
followed by translation or that the dehydrin production is too low to be
detectable.
Aquaporins are water channels, which can facilitate the passage of
water across biological membranes. In plants, aquaporins have been
localized to the tonoplast (TIP) and the plasma membrane (PIP); a third
subfamily, Nod-MIP, includes proteins homologous to Nod26, a protein
located in the peribacteriod membranes of symbiotic soybean root nodules
(reviewed in Maurel 1997). Five sunflower cDNAs belonging to the TIP
family were isolated by Sarda et al. (1999). Expression of the TIP-like genes
was studied in roots during 24 h water deprivation. Due to the changes in
their transcript levels, it is proposed that SunTIP aquaporins play a role in
the sunflower response to drought (Sarda et al. 1999).
The method of differential display reverse transcription PCR (DDRT-
PCR) was used to compare overall differences in gene expression between
drought- or salinity-stressed and unstressed (control) sunflower plants (Liu
and Baird 2003). Five drought-related cDNAs and 12 salinity-regulated
cDNAs were cloned and sequenced. Thirteen of these cDNAs were confirmed
to be expressed differentially in response to drought or salinity stress by
quantitative RT-PCR. Sequence analysis of these clones identified five of them
to show homology to known genes: guanylate kinase (signal transduction),
lytB (antibiotic/drug resistance), selenium-binding protein (heavy metal
stress), polyprotein (reverse transcriptase), and AC-like transposable element.
For one of the cDNA clones, HaABRC5, the full-length cDNA sequence was
obtained by completing the 5'-end by RACE (Liu and Baird 2004). The genomic
DNA sequence upstream of the transcription start site of HaABRC5 was cloned
by RAGE. The full-length cDNA contains an ORF of 423 nucleotides encoding
141 amino acids, including a “bipartite nuclear targeting sequence”. The
deduced amino acid sequence had no similarity to known genes in the
database. Quantitative RT-PCR showed that HaABRC5 is upregulated by
drought, high salinity, and exogenous application of abscisic acid (ABA).
Three ABRE (ABA responsive elements) were found within the HaABRC5
promoter region. Therefore, HaABRC5 is probably an ABA-responsive nuclear
protein playing a role in plant stress response (Liu and Baird 2004).
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