ZmNrat1 is a Novel Candidate Gene Differentially Induced by Al in Maize Contrasting Lines for Al Tolerance

Aluminum (Al) toxicity is an important limitation to food security in the tropics and subtropics. High Al saturation in acid soils limits root development and its ability to uptake water and nutrient. Al exclusion mechanism based on Al-activated organic acid release from root apices has been the major studied Al tolerance mechanisms in plants. However, in addition to prevent Al from entering the root, plants can neutralize internal Al once inside the cytosol. This physiological mechanism has recently been supported by the identification of other genes associated with Al tolerance, including Nramp aluminum transporter in rice (Nrat1). Nrat1 is an Al³⁺transporter located in the plasma membrane of root apical cells, suggesting its putative role in the internal Al detoxification mechanism. In maize, Al tolerance is known to be quantitatively inherited, and only the ZmMATE1 has been associated with Al tolerance in this species. Here we found a predicted maize homologue to Nrat1, sharing 83% amino acid sequence identity and localized within a genomic region highly associated with Al tolerance in a RIL population. ZmNrat1 was specifically expressed in maize roots, mainly in the first centimeter of the root apex after one hour of Al treatment. Additionally, the Al tolerant line (Cateto Al237) presented an early induction under Al treatment, compared with the Al sensitive line, which reached the highest expression peak after three hours of Al treatment. This expression pattern was highly compatible to the expression of the probe MZ00052211, representing this candidate gene, in a microarray experiment using root tips of two maize contrasting lines submitted to Al toxicity in nutrient solution. ZmNrat1 expression in maize also showed a same expression profile as Nrat1 in rice, suggesting that this candidate gene can be involved in maize Al tolerance. Financial support: FAPEMIG, CAPES, CNPq, Embrapa and GCP.