Abstract
Shoot zinc (Zn) concentration in Brassica oleracea is affected by soil Zn and phosphorus (P) supply. Most problematic is the negative impact of P fertilizers on Zn concentrations in crops, which makes balancing yield and mineral quality challenging. To evaluate early molecular mechanisms involved in the accumulation of large shoot Zn concentrations regardless of the P supply, two B. oleracea accessions differing in root architecture and root exudates were grown hydroponically for two weeks with different combinations of P and Zn supply. Ionome profiling and deep RNA sequencing of roots revealed interactions of P and Zn in planta, without apparent phenotypic effects. In addition, increasing P supply did not reduce tissue Zn concentration. Substantial changes in gene expression in response to different P and/or Zn supplies in roots of both accessions ensured nutritionally sufficient P and Zn uptake. Numerous genes were differentially expressed after changing Zn or P supply and most of them were unique to only one accession, highlighting their different strategies in achieving nutrient sufficiency. Thus, different gene networks responded to the changing P and Zn supply in the two accessions. Additionally, enrichment analysis of gene ontology classes revealed that genes involved in lipid metabolism, response to starvation, and anion transport mechanisms were most responsive to differences in P and Zn supply in both accessions. The results agreed with previously studies demonstrating alterations in P and Zn transport and phospholipid metabolism in response to reduced P and Zn supply. It is anticipated that improved knowledge of genes responsive to P or Zn supply will help illuminate the roles in uptake and accumulation of P and Zn and might identify candidate genes for breeding high-yield-high-Zn brassicas.
Highlights
Plants have an extraordinary ability to survive in a fluctuating environment
Responses to insufficient P and Zn supply were assessed by analyzing gene expression in roots of young B. oleracea plants, not yet exhibiting visible deficiency symptoms
A number of Zn and P-responsive genes were detected. Their expression changes were related to acclimation to low-nutrient environments and contributed to maintaining balanced nutrition
Summary
Plants have an extraordinary ability to survive in a fluctuating environment. When facing scarcity in essential mineral elements (nutrients) plants employ a plethora of morphological, physiological and metabolic acclimatory mechanisms to enhance nutrient acquisition and/or their within-plant utilisation (White and Brown, 2010; White et al, 2013b). In the case of zinc (Zn) deficiency, increased Zn uptake is achieved mainly by increasing Zn uptake capacity through a tightly regulated network of molecular interactions in which the coordinated expression of Zn transporters plays a major role in Zn acquisition from soil, in movement between organs and tissues and in intracellular sequestration of Zn (Assunção et al, 2010), chemical modification of the rhizosphere to increase Zn phytoavailability and greater exploration of the root volume are beneficial (White et al, 2013a). The requirements for P and Zn differ by orders of magnitude, i.e. 2,000–5,000 μg P g-1 dry weight (DW) and 15–30 μg Zn g-1 DW in most crops (White and Brown, 2010) and their roles in the plants are contrasting, they are both poorly mobile in soil and as such, traits involved in the increased acquisition of one can improve the acquisition of the other
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