Abstract
Background and aimsPlant and bacteria are able to synthesise proline, which acts as a compound to counteract the negative effects of osmotic stresses. Most methodologies rely on the extraction of compounds using destructive methods. This work describes a new proline biosensor that allows the monitoring of proline levels in a non-invasive manner in root exudates and nodules of legume plants.MethodsThe proline biosensor was constructed by cloning the promoter region of pRL120553, a gene with high levels of induction in the presence of proline, in front of the lux cassette in Rhizobium leguminosarum bv. viciae.ResultsFree-living assays show that the proline biosensor is sensitive and specific for proline. Proline was detected in both root exudates and nodules of pea plants. The luminescence detected in bacteroids did not show variations during osmotic stress treatments, but significantly increased during recovery.ConclusionsThis biosensor is a useful tool for the in vivo monitoring of proline levels in root exudates and bacteroids of symbiotic root nodules, and it contributes to our understanding of the metabolic exchange occurring in nodules under abiotic stress conditions.
Highlights
Drought and salinity stress are some of the environmental factors most affecting plant growth and crop yield worldwide
Proline catabolism is mediated by two enzymes; proline dehydrogenase (ProDH) producing pyrroline-5-carboxylate (P5C) from proline, and delta1-pyrroline-5-carboxylate dehydrogenase (P5CDH), which converts P5C to glutamate (Szabados and Savouré 2010)
The gene pRL120553 and pRL120554 was shown to be induced 16-fold and 2-fold respectively in R. leguminosarum bv. viciae 3841 when grown in the presence of proline (Ramachandran et al 2011)
Summary
Drought and salinity stress are some of the environmental factors most affecting plant growth and crop yield worldwide. In order to counteract the negative effects of osmotic stresses, plant and bacteria are able to synthesise osmoprotectant compounds to maintain cell viability. Proline catabolism is mediated by two enzymes; proline dehydrogenase (ProDH) producing pyrroline-5-carboxylate (P5C) from proline, and delta1-pyrroline-5-carboxylate dehydrogenase (P5CDH), which converts P5C to glutamate (Szabados and Savouré 2010). In bacteria, both steps are catalysed by a single polypeptide encoded by the gene putA, whose expression is regulated by putR and is induced in response to proline (Jimenez-Zurdo et al 1997; Keuntje et al 1995; Kohl et al 1988). This work describes a new proline biosensor that allows the monitoring of proline levels in a non-invasive manner in root exudates and nodules of legume plants
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