Phytosiderophores determine thresholds for iron and zinc accumulation in biofortified rice endosperm while inhibiting the accumulation of cadmium

Abstract

We unravel the mechanisms that set upper limits for iron and zinc accumulation in rice endosperm while inhibiting the accumulation of cadmium.

Iron and Zinc in the Embryo and Endosperm of Rice (Oryza sativa L.) Seeds in Contrasting 2′-Deoxymugineic Acid/Nicotianamine Scenarios

“…There was no correlation between NA and metals, whereas several correlations between metals were found, including Mn vs. Zn ( r = 0.782; P ≤ 0.01), Mn vs. Cu ( r = 0.725; P ≤ 0.01) and Fe vs. Zn ( r = 0.566; P ≤ 0.05). Correlations between Fe and Zn have been found in previous studies ( Lombi et al, 2011 ; Anuradha et al, 2012 ; Banakar et al, 2017b ; Kampuang et al, 2017 ), and are expected due to the fact that both metals share mechanisms for uptake, short- and long-distance transport in the plant and intracellular trafficking.…”

“…Other rice transgenics complying with this DMA/NA scenario are those overexpressing OsNAS1-3 ( Lee et al, 2009b ) or HvNAS1 alone ( Masuda et al, 2009 ), as well as OsNAS2 in combination with SoyferH1 ( Trijatmiko et al, 2016 ), which showed concentration increases in polished seeds (endosperm) of 2- to 33-fold for DMA, 5- to 32-fold for NA, 2.0- to 7.5-fold for Fe and 2.2- to 3.8-fold for Zn. The same scenario occurs when overexpressing OsNAS1 in combination with HvNAATb ( Banakar et al, 2017b ), leading to increases in polished seeds of 33-, 160-, 4.0-, and 4.1-fold for DMA, NA, Fe, and Zn concentrations, respectively; that study also shows an increased abundance of NA and DMA in leaves and roots, which promotes Fe and Zn uptake, root-to-shoot translocation, and finally seed loading. Other transgenics also showed concomitant Fe and Zn concentration increases, but the DMA and/or NA concentrations were not determined ( Wirth et al, 2009 ; Boonyaves et al, 2017 ; Wu et al, 2018 ).…”

“…Rice plants ( Oryza sativa L. cv EYI 105) were transformed to obtain genotypes overexpressing OsNAS1 and/or HvNAATb genes and therefore with high levels of NA and/or DMA. The details of the cloning, expression and transformation were described in detail in Banakar et al (2017b) . The six lines used are two overexpressing OsNAS1 alone (N1 and N2), two expressing HvNAATb alone (D1 and D2) and two expressing OsNAS1 and HvNAATb together (ND1 and ND2).…”

“…The six lines used are two overexpressing OsNAS1 alone (N1 and N2), two expressing HvNAATb alone (D1 and D2) and two expressing OsNAS1 and HvNAATb together (ND1 and ND2). Lines ND1 and ND2 were also used, although in different growth conditions, in Banakar et al (2017b) .…”

“…The fact that mutations in the genes involved in NA and DMA synthesis and those of YSL transporters do not cause substantial decreases in the seed Fe concentrations (e.g., osnas3 , Lee et al, 2009b ) supports that metal transport systems in plants are redundant. On the other hand, the fact that the overexpression of genes involved in DMA/NA synthesis and those of YSL transporters only lead to limited increases in seed Fe concentrations ( Banakar et al, 2017a , b ) support the existence of regulatory feedback loops. Once in the rice grain, Fe may be stored in ferritins to avoid toxicity ( Briat et al, 2010 ), sequestered in vacuoles ( Kim et al, 2006 ) or bound to phytate, a P-rich molecule preferentially located in the aleurone layer ( Persson et al, 2009 ).…”