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domesticated germplasm, demonstrating that wild sunflowers represent a
rich source of untapped resistance genes.
Radwan et al. (2003) concentrated on the non-TIR-NBS-LRR RGAs to
test whether RGA markers of this subclass of plant resistance genes could
be linked to Pl loci, which segregate independently of Pl 6 . They used one
degenerate (Leister et al. 1996; Yu et al. 1996) and four specific primer pairs,
which were designed using the sunflower RGA sequences of the four non-
TIR-NBS-LRR on LG 13 (Gedil et al. 2001). The amplification products were
cloned, sequenced and used as RFLP probes to group RGAs with identical
RFLP profiles in the same class. A total of 16 RGAs were identified and
distinguished into six classes of RGA. Two of these classes correspond to
the TIR-NBS-LRR type while the remaining four classes correspond to the
non-TIR-NBS-LRR type of resistance genes. BSA was used to identify
polymorphic RGA fragments (Ha-NTIR7, Ha-NTIR11, Ha-NTIR2, Ha-
NTIR3) and those were scored on 150 F 2 plants of each cross. All the non-
TIR-LRR RGAs were found to be linked to Pl 5 and Pl 8 . Thus, Gentzbittel et
al. (1998), Gedil et al. (2001), Bouzidi et al. (2002) and Radwan et al. (2003)
provided evidence that TIR-NBS-LRR sequences as well as non-TIR-NBS-
LRR sequences exist in the sunflower genome.
In order to develop markers for MAS, Radwan et al. (2004) used the
partial sequence of two RGAs, Ha-NTIR11 and Na-NTIR3 (Radwan et al.
2003), to clone and map two full-length RGAs. The two sequences were
used to develop 14 STS markers, which are clustered within a genetic distance
of about 13.6 cM and 16.7 cM, for the Pl 5 and Pl 8 loci, respectively.
Furthermore, Radwan et al. (2005) investigated the transcriptional regulation
of the full-length RGA Ha-NTIR11g (Radwan et al. 2004). They compared
the expression level of Ha-NTIR11g at different times in resistant (QIR, Pl 8 )
and susceptible (CAY) lines without infection, after infection with P. halstedii ,
after treatment with signaling molecules such as salicylic acid, methyl-
jasmonic acid, hydrogen peroxide, and after wounding. The results show
that HaNTI11g is constitutively expressed at a low level in the healthy
hypocotyls and cotyledons of the resistant genotype, but not in the
susceptible genotype. The expression level of Ha-NTIR11g increased in the
resistant genotype only after infection with P. halstedii , but not after
wounding or treatment with signaling molecules. Thus, a relation between
infections with P. halstedii and the expression of Ha-NTIR1g1 seems to exist.
Recently, Radwan et al. (2008) identified 630 NBS-LRR homologs in
sunflower by database analysis and sequencing of DNA fragments spanning
conserved NBS sequences, which were isolated from common and wild
sunflower species. They developed DNA markers from 196 unique NBS-
LRR sequences and mapped 167 NBS-LRR loci. NBS-LRR loci were
distributed in cluster or singleton throughout the sunflower genome. On
LG 8, in the region of the downy mildew resistance loci Pl 1 , Pl 2 , Pl 6 , the
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