Agriculture Reference
In-Depth Information
Natural Variation in Model Plants as a Tool to Improve
Crop Quality
Restrictive regulations for commercial breeding of genetically modified plants have
persuaded breeders and scientists to look for alternative methods to improve crop
yield and quality. The result is a growing interest in naturally occurring genotypic
variation. The enhancement of crop productivity is fundamental for human society.
Therefore, exploring natural variation is of rapidly increasing importance to
improve quality aspects that are associated with the chemical composition of
agricultural products. The potential of wild species in the analysis of the molecular
genetic basis of plant nutrition for crop improvement was recognised a century ago
(Bessey
1906
), however this area of research started to expand only recently (Fernie
et al.
2006
; McCouch
2004
; Zamir
2001
).
To investigate natural variation in model plants and in crops two main
approaches are used. The first, the more traditional and still most popular way, is
quantitative trait loci (QTL) analysis (Koornneef et al.
2004
). It is based on the
mapping of segregating populations such as a RILs derived from the crosses
between two or more parental accessions. This leads to the localisation in the
genome of loci exerting a control of a complex phenotypic trait in a given envi-
ronment. A second approach is to use
Arabidopsis
natural accessions to identify
polymorphisms associated with adaptation by exploiting a genome-wide associa-
tion mapping (GWAS) also called linkage disequilibrium (LD) (Atwell et al.
2010
).
In contrast to QTL, in GWAS there are no crosses or pedigrees required, which
makes it easier to collect the data. It also has advantages over QTL analysis because
there are usually more alleles in the mixed population than in the two parents of the
cross (Myles et al.
2009
).
Mineral use efficiency, root uptake, translocation of nutrients from the roots to
the shoots, and their accumulation in the seeds are the traits that, with many others,
undergo a substantial natural variation. To date the QTL studies in crops have been
focused mainly on seed or leaf mineral concentration in rice, wheat, barley,
soybean, and
Brassica
species (Alonso-Blanco et al.
2009
). Natural variation pro-
vides a complementary resource to discover novel gene functions as well as the
variants of alleles that interact specifically with the genetic background or environ-
mental changes, which is of great interest for the study focused on plant adaptation
(Benfey and Mitchell-Olds
2008
). This approach also allows creation of correlation
networks between different nutrients that provide an overview of plant demands in
various environments (Buescher et al.
2010
). For example, a recent QTL study has
identified a group of six genes which are involved in complex control of the mineral
homeostasis in
Arabidopsis thaliana
(Ghandilyan et al.
2009
). These results illus-
trate that the study of natural variation has significantly expanded our understanding
of plant mineral nutrition, its regulation, and plant adaptation to environmental
changes. The wide genetic variation allows the modification of quantitative traits
that often could not be achieved through mutagenesis or transgenic approaches.
They should therefore be of major interest for commercial agriculture. More detailed
descriptions of natural variation approaches can be found in Chap.
2
of this topic.
