The combined strategy for iron uptake is not exclusive to domesticated rice

Abstract

Iron (Fe) is an essential micronutrient that is frequently inaccessible to plants. Rice (Oryza sativa L.) plants employ the Combined Strategy for Fe uptake, which is composed by all features of Strategy II, common to all Poaceae species, and some features of Strategy I, common to non-Poaceae species. To understand the evolution of Fe uptake mechanisms, we analyzed the root transcriptomic response to Fe defciency in O. sativa and its wild progenitor O. rufpogon. We identifed 622 and 2,017 diferentially expressed genes in O. sativa and O. rufpogon, respectively. Among the genes up-regulated in both species, we found Fe transporters associated with Strategy I, such as IRT1, IRT2 and NRAMP1; and genes associated with Strategy II, such as YSL15 and IRO2. In order to evaluate the conservation of these Strategies among other Poaceae, we identifed the orthologs of these genes in nine species from the Oryza genus, maize and sorghum, and evaluated their expression profle in response to low Fe condition. Our results indicate that the Combined Strategy is not specifc to O. sativa as previously proposed, but also present in species of the Oryza genus closely related to domesticated rice, and originated around the same time the AA genome lineage within Oryza diversifed. Therefore, adaptation to Fe2+ acquisition via IRT1 in fooded soils precedes O. sativa domestication.