Shoot Calcium and Magnesium Concentrations Differ between Subtaxa, Are Highly Heritable, and Associate with Potentially Pleiotropic Loci in Brassica oleracea      

Abstract

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 5 9) from natural populations. These accessions and 74 modern F 1 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 Ca 21 and Mg 21 uptake and homeostasis at the molecular level.

Mapping QTLs for mineral accumulation and shoot dry biomass under different Zn nutritional conditions in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

“…This could be due to a large number of QTLs involved in mineral accumulation but each with minor effect and therefore is difficult to be detected. Co-localization of QTLs involved in different minerals was reported previously for Arabidopsis seed mineral content with most of the co-localizations of K/Ca and K/Ca/Mn QTLs (Vreugdenhil et al 2004) and recently for Brassica oleracea shoot Ca/Mg concentrations (Broadley et al 2008). Although we found strong correlation between Mg, Ca and Sr concentrations, we only found QTLs for Mg and Sr, but these were the only mineral QTLs that co-localized in the studied population.…”

“…A two-fold genotypic variation was reported for Ca, Mg, K, Fe, Zn concentration among B. oleracea vegetables (Kopsell et al 2004;Broadley et al 2008) and for shoot dry biomass ratio-based Zn efficiency for B. napus and B. juncea (Grewal et al 1997). The observed natural variation for these traits in Brassica crops suggests the possibility to analyze these traits genetically.…”

“…These studies have demonstrated the presence of allelic variation affecting mineral accumulation, although the identity of the underlying genes remains unknown. However, very little is known about the genetics of mineral concentration in leafy vegetables, such as B. rapa vegetables, until recently QTLs were identified for shoot Ca and Mg concentrations in Brassica oleracea (Broadley et al 2008).…”

Eats roots and leaves. Can edible horticultural crops address dietary calcium, magnesium and potassium deficiencies?

“…While heritable natural genetic variation has been demonstrated, horticultural crops with greater mineral concentrations have apparently not yet been bred conventionally, yet a 50% increase appears a feasible breeding target (4) (Table 3). For example, leaf or shoot Ca and Mg concentration varies by > 50% among varieties and accessions of B. oleracea (27)(28)(29)(30) , Brassica rapa (31) , spinach (S. oleracea) (32) , onion (Allium cepa) (33) and chickpea (Cicer arietinum) (34) . (27,35) .…”

“…For example, leaf or shoot Ca and Mg concentration varies by > 50% among varieties and accessions of B. oleracea (27)(28)(29)(30) , Brassica rapa (31) , spinach (S. oleracea) (32) , onion (Allium cepa) (33) and chickpea (Cicer arietinum) (34) . (27,35) . In roots, up to 8-fold variation in Ca and 4 .…”