Cloning and sequencing of the cDNAs induced by aluminium treatment and P_i starvation in cultured tobacco cells

With the ultimate purpose of clarifying the mechanism for aluminium (Al) toxicity and for Al tolerance, we tried to isolate cDNAs whose expression is induced by Al treatment and phosphate (P_i) starvation. We performed P_i starvation and Al treatment (two‐step treatment) on suspension‐cultured cells of Nicotiana tabacum L. cv. Samsun and then constructed a cDNA library using poly(A)⁺‐RNA derived from the treated cells. Four independent cDNA clones (pAL 111, 139, 141 and 142) were isolated from the library by differential screening. Northern blot hybridization analysis indicated that the expression of these clones was induced by P_i starvation. Furthermore, we found that pAL 111 and pAL 142 are also induced by Al treatment. The complete cDNA sequencing of these 4 clones was determined. The results indicated that pAL111 is identical to the parA gene of N. tabacum, which is described as an auxin‐regulated gene and that pAL142 is highly homologous to the parB gene of N. tabacum whose product has glutathione S‐transferase (GST, EC 2.5.1.18) activity. Furthermore, we found a cysteine‐rich domain in the amino acid sequence of pAL139. No DNA and deduced amino acid sequences homologous to the pAL141 were found.