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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Shoot Calcium and Magnesium Concentrations Differ between Subtaxa, Are Highly Heritable, and Associate with Potentially Pleiotropic Loci in Brassica oleracea^1,[W],[OA]

Plant Sciences Division, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, United Kingdom (M.R.B., M.C.M.); Warwick HRI, University of Warwick, Wellesbourne, Warwick CV35 9EF, United Kingdom (J.P.H., D.A., H.C.B., A.M., D.A.C.P., G.R.T., R.M.H., W.P.S.); Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, United Kingdom (G.J.K.); and The Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, United Kingdom (P.J.W.)

Calcium (Ca) and magnesium (Mg) 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 of 376 accessions to capture a high proportion of species-wide allelic diversity within domesticated Brassica oleracea, 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- 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% to 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 (Arabidopsis thaliana) 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.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Martin R. Broadley (martin.broadley{at}nottingham.ac.uk).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.114645

^* Corresponding author; e-mail martin.broadley{at}nottingham.ac.uk.

Received December 6, 2007; accepted February 13, 2008; published February 15, 2008.