Isolation and characterization of wheat aluminum-regulated genes: possible involvement of aluminum as a pathogenesis response elicitor.

Using differential screening of a root tip cDNA library prepared from an Al-tolerant wheat cultivar (Triticum aestivum L. cv. Atlas-66) exposed to Al, we have isolated and characterized several wheat aluminum-regulated (War) cDNAs. Sequence comparison revealed that genes up-regulated by Al correspond to peroxidase (war4.2), cysteine proteinase (war5.2), phenylalanine-ammonia lyase (war7.2), and oxalate oxidase (war13.2). Two wheat cultivars that differ in their level of tolerance (cv. Atlas-66: tolerant, and cv. Fredrick: sensitive) were used to evaluate the relationship between the accumulation of War mRNAs and Al toxicity, as measured by root growth inhibition (RGI). The mRNA accumulation was modulated to similar levels in both cultivars compared at equivalent RGIs. This indicates that War mRNA accumulation is associated with the toxicity of Al rather than with the cultivar's tolerance. It appears that most of the genes found to be up-regulated by Al share homologies with genes induced by pathogens. This suggests that Al may act as an elicitor of a pathogenesis-related transduction pathway. The potential functions of the up-regulated war genes in cell wall strengthening and Al trapping are discussed.