The symbiosis phenotype and expression patterns of five nodule-specific genes of Astragalus sinicus under ammonium and salt stress conditions.

In previous works, we isolated 14 nodule-specific or nodule-enhanced genes from Astragalus sinicus by suppressive subtractive hybridization. In this study, we have further identified the expression patterns of five nodule-specific genes of A. sinicus under salt and ammonium stress. Transcription levels of genes tested were quantified by quantitative fluorescence real-time RT-PCR. Results showed that: (1) About 80 mM NaCl and all stress treatments containing (NH(4))(2)SO(4) significantly inhibited nitrogen-fixing capacity of inoculated plants. About 40 mM NaCl showed relative lighter inhibition. (2) Compare with positive control at normal conditions, the expressions of all genes were significantly reduced by all ammonium stress. (3) Under salt stress without exogenous nitrogen, transcription levels of AsIIA255 and AsE246 were significantly increased after treatment for 3 days. But expressions of AsG2411, AsIIC2512, and AsB2510 were suppressed by 80 mM NaCl and not significantly affected by 40 mM NaCl. (4) Under salt stress with exogenous nitrogen, expressions of AsG2411, AsIIC2512, AsB2510, and AsIIA255 were significantly suppressed. While, the transcription level of AsE246 under 80 mM NaCl containing 1 mM (NH(4))(2)SO(4) was still higher than that of positive control. The correlation of the expression profiles of three cysteine cluster protein (CCP) genes (AsG2411, AsIIC2512, AsIIA255) and one lipid transfer protein (LTP) gene (AsE246) with the nitrogen-fixing capacities of nodules in each treatments may explain the molecular mechanisms of their supposed functions in symbiosis and nitrogen-fixing process. Our results also implied that AsIIA255 and AsE246 might play a role in the response of A. sinicus to salt stress to facilitate the nitrogen-fixation process.