Abstract
1-Aminocyclopropane-1-carboxylate (ACC) deaminase is a plant growth promoting (PGP) trait found in beneficial bacteria including streptomycetes and responsible for stress modulation. The ACC deaminase gene, acdS, of S. venezuelae ATCC 10712 was cloned into an expression plasmid, pIJ86, to generate S. venezuelae/pIJ86-acdS. Expression of acdS and production of ACC deaminase of S. venezuelae/pIJ86-acdS were significantly higher than the unmodified strain. The ACC deaminase-overexpressing mutant and the wild type control were inoculated into Thai jasmine rice (Oryza sativa L. cv. KDML105) under salt stress conditions. S. venezuelae on its own augmented rice growth and significantly increased more tolerance to salinity by reduction of ethylene, reactive oxygen species (ROS) and Na+ contents, while accumulating more proline, total chlorophyll, relative water content (RWC), malondialdehyde (MDA), and K+ than those of uninoculated controls. The overproducer did not alter chlorophyll, RWC, or MDA further–while it did boost more shoot weight and elongation, and significantly regulated salt tolerance of rice by increasing proline and reducing ethylene and Na+ contents further than that of the wild type. This work is the first illustration of the beneficial roles of S. venezuelae to enhance plant fitness endophytically by promotion of growth and salt tolerance of rice.
Highlights
Streptomycetes have been recognized recently as plant growth promoting (PGP) bacteria that can protect plants from infectious diseases and enhance plant growth through several PGP-traits, such as siderophore production, plant hormone production, and phosphate solubilization[4,5,6]
ACC deaminase is a bacterial enzyme found in several PGP-bacteria including Bacillus, Enterobacter, Pseudomonas and Streptomyces
In this work ACC deaminase gene (acdS), encoding ACC deaminase located in the genome of S. venezuelae ATCC 10712, was cloned and expressed in this strain
Summary
Streptomycetes have been recognized recently as plant growth promoting (PGP) bacteria that can protect plants from infectious diseases and enhance plant growth through several PGP-traits, such as siderophore production, plant hormone production, and phosphate solubilization[4,5,6]. The genome sequence has never been inspected for a role of plant-beneficial functions; likewise, S. venezuelae has never been documented as a PGP-endophytic bacterium. Genes contributing to PGP-traits including acdS were present in genome sequences of PGP-rhizobacteria (PGPR) and found in those of non-PGPR20,21. On this basis, we examined genes related to PGP-function in all genome sequences of members of a genus Streptomyces available in the GenBank database, in particular acdS. AcdS was present in many genomes of non-PGP-endophytic Streptomyces, including S. venezuelae. The effects of overexpression of acdS within S. venezuelae towards rice growth and salt tolerance were investigated. The physiology of rice associated with S. venezuelae and its overexpressed mutant under salt stress condition are discussed
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