Discrimination of genes expressed in response to the ionic or osmotic effect of salt stress in soybean with cDNA-AFLP

Abstract

'Ionic effects' and 'osmotic effects' are major components of salt stress in plants. In this study these two parameters were clearly discriminated in soybean (Glycine max (L.) Merr.) using a modified cDNA-amplified fragment length polymorphism (AFLP) technique. Soybean (cv. Lee) seedlings were exposed to iso-osmotic treatment consisting of 100 mM NaCl and 12% (w/v) polyethylene glycol 6000 for 24 h. The NaCl treatment fully activated salt tolerance as confirmed by the expression of the inositol-1-phosphate synthase gene. Then, gene expression in each sample was examined by cDNA-AFLP, and 140 differentially expressed cDNA fragments were obtained out of 13 000 amplicons. The percentage of transcripts dependent on ionic (NaCl-specific) and osmotic effects (common with NaCl and polyethylene glycol) could be evaluated for 44 and 40% of them, respectively. cDNA-AFLP also revealed the distribution of transcripts in shoots and roots. The ionic effect-dependent gene expression was more abundant in roots indicating that they showed a greater response to ionic stress than shoots. Several ion transporters, transcription factors and redox enzymes that were specific to the ionic effect may play important roles in the salt tolerance of soybean. The technical advantages of this modified cDNA-AFLP method are also discussed.