2008 年 7.2 巻 1 号 p. 20-24
To remediate the worldwide-spreading acid sulphate soil area and utilize it for human beings, acid tolerant leguminous plants are expected to be useful as crops and pioneer plants. The purpose of this study is to produce symbiotic nitrogen fixing systems tolerant to acid sulfate soils, through the identification of the genes that confer acid tolerance on plants and the isolation of acid-tolerant rhizobia. We identified acid tolerant genes by two approaches. One approach is functional screening of a soybean cDNA library and their characterization in planta. E. coli cells were transformed with a cDNA library of soybean and cultured on a LB medium adjusted to pH 4 or pH 5. Selected six tolerant clones were introduced into Arabidopsis thaliana using a plant expression vector. The overexpressors grew better than the wild type under the acid and aluminium stresses. The other one is molecular genetic analysis of the candidate genes identified by previous studies: a gene for a key enzyme of sulfur assimilation, cysteine synthase. The candidate gene was ectopically overexpressed in A. thaliana under the control of the cauliflower mosaic virus 35S promoter. All the genes tested were shown to confer acid tolerance on the model plants.