cDNA clones encoding 1,3-beta-glucanase and a fimbrin-like cytoskeletal protein are induced by Al toxicity in wheat roots

A cDNA library made from mRNA of Al-treated roots of an Al-sensitive wheat (Triticum aestivum cv Victory) cultivar was screened with a degenerate oligonucleotide probe derived from the partial amino acid sequence of the Al-induced protein TAl-18. Of seven clones that initially hybridized with the probe, one encoded a novel 1,3-beta-glucanase having a calculated molecular weight of 46.3 and an isoelectric point of 6.0. Like the A6 1,3-beta-glucanase gene products from Brassica napus and Arabidopsis thaliana, the predicted wheat protein had a C-terminal extension with three potential glycosylation sites. Northern analysis revealed that wheat 1,3-beta-glucanase mRNA was up-regulated in Al-intoxicated roots, with highest expression after 12 h. The antibody to A6 1,3-beta-glucanase from B. napus cross-reacted with a 56-kD protein that was induced after 24 h. A second partial cDNA clone showed similarity to genes encoding cytoskeletal fimbrin-like (actin-bundling) proteins. Although well studied in animals and fungi, fimbrins have not previously been described in plants. Fimbrin-like transcripts were up-regulated after 24 h of Al treatment in the Al-sensitive wheat cv Victory. In the Al-tolerant cv Atlas 66, fimbrin-like mRNA was up-regulated within 12 h by Al concentrations that did not inhibit root growth. Cellular stress associated with Al toxicity therefore causes up-regulation of a defense-related gene and a gene involved in the maintenance of cytoskeletal function.