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ORS686, and CRT162) and the phenotypic marker locus T cosegregated
and were tightly linked to Ms10 at a genetic distance of less than 1 cM
(Pérez-Vich et al. 2005). The availability of tightly linked PCR markers will
facilitate marker-assisted breeding programs and provide a basis for physical
mapping and map-based-cloning of theses genes. Chen et al. (2006)
identified DNA markers linked to the Ms9 gene in an F 2 population derived
from a cross between NMS360 and RHA271 and mapped the Ms9 gene
with SSR markers to LG 10 of the public sunflower map (Yu et al. 2003). The
target region amplified polymorphism (TRAP) marker technique, applied
by Chen et al. (2006), is a method that uses expressed sequence tag (EST)
sequences and bioinformatic tools to generate polymorphic markers around
targeted candidate gene sequences (Hu and Vick 2003). Four fixed primers
derived from published male sterility inducing genes from wheat (Chen et
al. 2005), Arabidopsis (Rubinelli et al. 1998; Stintzi and Browse 2000) and
maize (Albertsen et al. 1993) were combined with three arbitrary primers.
Six of the amplified TRAP markers were linked to the Ms9 gene, and two of
them, Ts4p03-202 and Tt3p09-529, cosegregated with the Ms9 gene. These
two markers will facilitate isolation of the Ms9 gene by map-based cloning.
CMS, a phenotype in higher plants in which plants are not able to
produce or shed any functional pollen, has been associated with chimeric
open-reading frames (ORFs) in the mitochondrial genomes (for review see
Horn 2006). These ORFs encode proteins that interfere with mitochondrial
functions during pollen development. In sunflower, commercial hybrid
breeding is based on a single source of male sterility, PET1. This male sterility
originated from an interspecific cross between Helianthus petiolaris Nutt and
Helianthus annuus L. (Leclercq 1969) . Alterations in the mitochondrial genome
of PET1 and fertile lines are limited to a 17-kb region and consist of two
mutations: a 12-kb inversion and a 5-kb insertion/deletion, which lead to
an altered transcription pattern of the atp A gene (Siculella and Palmer 1988).
CMS is associated with the expression of a novel ORF, orfH522 (Köhler et al.
1991) that encodes a 16 kDa polypeptide (Horn et al. 1991; Laver et al. 1991).
Nuclear genes known as restorer of fertility ( Rf ) genes have the function to
suppress the effect of CMS-associated mitochondrial abnormality on male
fertility e.g., reducing the anther-specific level of the cotranscript of atp A-
orfH522 in the male florets (Monéger et al. 1994). Several restorer lines are
available for PET1; most of them carry the genes Rf1 and Rf 2 restoring pollen
fertility. Rf 2 was described to be present in nearly all inbred lines, including
maintainers of PET1 (Miller and Fick 1997) and only Rf1 gene is introduced
by the restorer lines to produce fertile sunflower hybrids. Map-based cloning
efforts were started by several groups to isolate the restorer gene Rf1 . The
Rf1 gene was mapped to LG 6 in the RFLP map and the consensus map
(Gentzbittel et al. 1995, 1999) together with the Pl 5 locus conferring resistance
to downy mildew (Bert et al. 2001). Horn et al. (2003) developed PCR-based
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