Aluminum Alleviation of Iron Deficiency Chlorosis Is Conserved in Wild Rice Relative Oryza rufipogon and in Maize

Aluminum (Al), an element that has no biological function described in plants, is commonly found in acidic soils, reducing plant growth, despite some beneficial effects reported in the literature. Iron (Fe) is an essential nutrient for plants, and Fe deficiency causes leaf interveinal chlorosis. Remarkably, rice (Oryza sativa), a C₃ crop considered tolerant to Al, shows alleviation of Fe deficiency chlorosis when exposed to Al, suggesting that Al can positively impact Fe homeostasis. However, whether this effect is observed only in rice or is common to other plant species is unknown. The rice wild progenitor Oryza rufipogon is closely related to the domesticated species, sharing several traits such as a semi-aquatic habit and use of the combined strategy for Fe uptake. Maize (Zea mays), on the other hand, is a C₄ plant, adapted to well-aerated soils, and uses a classic chelation-based strategy for Fe uptake. Here we used these two Poaceae representatives to determine whether Al excess could alleviate Fe deficiency chlorosis in species other than rice. Although Al caused toxicity irrespective of Fe levels, its addition essentially abolished chlorosis in Fe-deficient plants. The expression of Fe deficiency-induced marker genes was reduced to control levels in both species, suggesting that the Al alleviation effect leads to systemic signaling and down-regulation of Fe uptake mechanisms. Al alleviation partially rescued photosynthetic machinery inhibited by Fe deficiency, suggesting that leaves are maintaining photosynthetic activity when Al is present even under low Fe conditions. Taken together, our data show that the Al alleviation effect is shared by two other Poaceae species in addition to O. sativa and suggest that it might not be directly linked to domestication, changes in C₃/C₄ metabolism, or Al tolerance levels found in different species.