Agriculture Reference
In-Depth Information
reveals the existence of homologous QTL for traits involved in domestication, such
as plant height and maturity, as well as tolerance to abiotic stress, within the cereals
(Chardon et al. 2005 ; Hanocq et al. 2007 ; Li et al. 2013 ; Swamy et al. 2011 ). A
recent example of meta-QTL analysis of a nutrition use efficiency-related trait
comes from the dissection of an ortho-metaQTL in bread wheat by Quraishi
et al. ( 2011 ). The authors identified a major NUE ortho-metaQTL conserved at
orthologous positions in wheat, rice, sorghum and maize. Starting from three
independent studies reporting QTL detection for traits related to NUE components
in wheat, the authors proposed that a glutamate synthase (GoGAT) gene is con-
served structurally and functionally at orthologous positions in rice, sorghum and
maize genomes, and it that may contribute to NUE in wheat and other cereals.
Exploiting Genetic Variation in Wild Populations to Reveal
NUE Genes by Association Mapping
First Results Obtained on Arabidopsis to Reveal NUE Genes
Over the past 10 years, traditional QTL mapping has led to the identification of
sequence variants that modulate a range of physiological and developmental traits.
Prior knowledge of the biological function of the affected genes was often helpful
in identifying them, but increasingly the responsible locus is found to encode a
protein without known biochemical function (Lempe et al. 2005 ). Apart from
alleles that alter expression levels or protein function, a surprising number of drastic
mutations such as deletions and stop codons underlie phenotypic variation. Some of
these changes are found in many accessions (Weigel and Mott 2009 ) suggesting
that they are adaptive. Nevertheless, despite some success stories, the number of
known alleles responsible for phenotypic variation among accessions remains
limited, mostly because fine mapping and dissection of QTLs are time consuming.
Arabidopsis thaliana was the first plant species for which a genome sequence
became available (Arabidopsis Initiative 2000 ). This initial sequence was from a
single, high quality, inbred strain (accession) with each chromosome represented by
only two contigs, one for each arm. In addition to functional analyses, the 120 Mb
reference sequence of the Columbia (Col-0) accession proved to be a boon for
evolutionary and ecological researches. A particular advantage in this respect is that
the species is mostly self-fertilising, and most strains collected from the wild are
homozygous throughout the genome (Weigel and Mott 2009 ). This distinguishes
Arabidopsis from other model organisms such as the mouse or the fruit fly. In these
systems, inbred strains have been derived, but they do not represent any individual
actually found in nature. Numerous plants genomes have been completely
sequenced and released recently.
Natural Arabidopsis accessions show tremendous genetic and phenotypic diver-
sity. Thus far, significant natural variation has been reported for every phenotypic
Search WWH ::




Custom Search