Properties of Astragalus sp. microsymbionts and their putative role in plant growth promotion
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ORIGINAL PAPER
Properties of Astragalus sp. microsymbionts and their putative role in plant growth promotion Sylwia Wdowiak‑Wróbel1 · Wanda Małek1
Received: 12 April 2016 / Revised: 6 May 2016 / Accepted: 11 May 2016 © The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract The plant growth-promoting rhizobacteria have developed many different (indirect and direct) mechanisms that have a positive effect on plant growth and development. Strains isolated from Astragalus cicer and Astragalus glycyphyllos root nodules were investigated for their plant growth-promoting properties such as production of indole3-acetic acid (IAA) and siderophores, phosphate solubilization, ACC deaminase activity, and tolerance to heavy metals. IAA production and P-solubilization were frequent features in the analysed strains, while siderophores were not produced by any of them. In this work, we investigated the presence of the acdS genes and ACC deaminase activities in Astragalaus cicer and A. glycyphyllos microsymbionts, classified within the genus Mesorhizobium. The results demonstrated that the acdS gene is widespread in the genome of Astragalus sp. microsymbionts; however, none of the tested strains showed ACC deaminase activity. The acdS gene sequence similarity of the analysed strains to each other was in the range from 84 to 99 %. On the phylogram of acdS gene sequences of milkvetch, the symbionts clustered tightly with the genus Mesorhizobium bacteria.
Communicated by Erko Stackebrandt. Electronic supplementary material The online version of this article (doi:10.1007/s00203-016-1243-3) contains supplementary material, which is available to authorized users. * Sylwia Wdowiak‑Wróbel [email protected] 1
Department of Genetics and Microbiology, Maria Curie Skłodowska University, Akademicka 19 St., 20‑033 Lublin, Poland
Keywords Astragalus sp. microsymbionts · acdS gene · PGPR
Introduction Ethylene affects plant growth and development. It is responsible for several processes in plants and, depending on the level, can e.g. promote root initiation, inhibit root elongation, activate plant hormone synthesis, and promote flower wilting. Ethylene is also involved in the response to both biotic and abiotic stresses. An increase in ethylene synthesis may accompany for example extreme temperatures, water flooding, drought, radiation, salinity, and presence of various pathogens. It has also been described that ethylene affects various stages of symbiosis (Vacheron et al. 2013; Glick 2014). Ethylene can inhibit nodule development in different fabacean plants, for example in Phaseolus vulgaris, Lotus japonicas, and Trifolium repens (Tamimi and Timko 2003). In the literature, there is a “stress ethylene” concept. The model of “stress ethylene” includes the synthesis of ethylene in two peaks. The first one is small and reflects ethylene that consumes the pool of ACC (1-aminocyclopropane1-carboxylate) existing in stressed plant tissues. Probably, this ethylene is responsible for initiation
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