Evaluation of the role of genes encoding for Δ1-pyrroline-5-carboxylate synthetase (P5CS) during drought stress in arbuscular mycorrhizal Glycine max and Lactuca sativa plants

In this study, we have determined whether the arbuscular mycorrhizal, (AM) symbiosis is able to alter the pattern of Delta(1)-pyrroline-5-carboxylate synthetase (p5cs) gene expression under drought stress and whether such possible alteration functions in the protection of the host plants against drought. To achieve this, we cloned a P5CS-encoding gene from Glycine max (gmp5cs) and another from Lactuca sativa (lsp5cs) and analyzed their contribution to the response against drought in control and AM soybean and lettuce plants. The analysis of gmp5cs and lsp5cs gene expression showed that these genes were up-regulated by drought stress. The highest gene expression was found in non-inoculated plants subjected to drought. A contrasting result was obtained in soybean plants singly inoculated with Bradyrhizobium japonicum, where the gmp5cs gene showed little up-regulation in roots under drought stressed conditions. Moreover, both soybean and lettuce AM plants showed lower p5cs transcript accumulation under drought stress than non-inoculated plants. The present results indicate that the induction of p5cs gene is not a mechanism by which the AM symbiosis protects their host plant against drought. (c) 2005 Elsevier Ltd. All rights reserved.