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Plant Physiology Preview Published on February 15, 2008; 10.1104/pp.107.114645
OPEN ACCESS ARTICLE
Received December 6, 2007 Shoot calcium (Ca) and magnesium (Mg) concentrations differ between subtaxa, are highly heritable, and associate with potentially pleiotropic loci in Brassica oleracea
Plant Sciences Division, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire, LE12 5RD, UK; Warwick HRI, University of Warwick, Wellesbourne, Warwick CV35 9EF, UK; Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK; The Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, UK * Corresponding author; email: martin.broadley{at}nottingham.ac.uk.
Calcium and magnesium are the most abundant Group II elements in both plants and animals. Genetic variation in shoot Ca and shoot Mg concentration (shoot-Ca and Mg) in plants can be exploited to biofortify food crops and thereby increase dietary Ca and Mg intake for humans and livestock. We present a comprehensive analysis of within-species genetic variation for shoot-Ca and Mg, demonstrating that shoot mineral concentration differs significantly between subtaxa (varietas). We established a structured diversity foundation set (DFS) of 376 accessions to capture a high proportion of species-wide allelic diversity within domesticated Brassica oleracea L., including representation of wild relatives (C-genome, 1n=9) from natural populations. These accessions, and 74 modern F1 hybrid cultivars, were grown in glasshouse and field environments. Shoot-Ca and Mg varied 2-fold and 2.3-fold respectively, and was typically not inversely correlated with shoot biomass, within most subtaxa. The closely-related capitata (cabbage) and sabauda (Savoy cabbage) subtaxa consistently had the highest mean shoot-Ca and Mg. Shoot-Ca and Mg in glasshouse-grown plants was highly correlated with data from the field. To understand and dissect the genetic basis of variation in shoot-Ca and Mg, we studied homozygous lines from a segregating B. oleracea mapping population. Shoot-Ca and Mg was highly heritable (up to 40%). Quantitative trait loci (QTL) for shoot-Ca and Mg were detected on chromosomes C2, C6, C7, C8 and, in particular, C9 where QTL accounted for 14-55% of the total genetic variance. The presence of QTL on C9 was substantiated by scoring recurrent backcross substitution lines, derived from the same parents. This also greatly increased the map resolution, with strong evidence that a 4 cM region on C9 influences shoot-Ca. This region corresponds to a 0.41 Mb region on Arabidopsis Chromosome 5 that includes 106 genes. There is also evidence that pleiotropic loci on C8 and C9 affect shoot-Ca and Mg. Map-based cloning of these loci will reveal how shoot-level phenotypes relate to Ca2+ and Mg2+ uptake and homeostasis at the molecular level.
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