Abstract
Stenotrophomonas rhizophila has great potential for applications in biotechnology and biological control due to its ability to both promote plant growth and protect roots against biotic and a-biotic stresses, yet little is known about the mode of interactions in the root-environment system. We studied mechanisms associated with osmotic stress using transcriptomic and microscopic approaches. In response to salt or root extracts, the transcriptome of S. rhizophila DSM14405T changed drastically. We found a notably similar response for several functional gene groups responsible for general stress protection, energy production, and cell motility. However, unique changes in the transcriptome were also observed: the negative regulation of flagella-coding genes together with the up-regulation of the genes responsible for biofilm formation and alginate biosynthesis were identified as a single mechanism of S. rhizophila DSM14405T against salt shock. However, production and excretion of glucosylglycerol (GG) were found as a remarkable mechanism for the stress protection of this Stenotrophomonas strain. For S. rhizophila treated with root exudates, the shift from the planktonic lifestyle to a sessile one was measured as expressed in the down-regulation of flagellar-driven motility. These findings fit well with the observed positive regulation of host colonization genes and microscopic images that show different colonization patterns of oilseed rape roots. Spermidine, described as a plant growth regulator, was also newly identified as a protector against stress. Overall, we identified mechanisms of Stenotrophomonas to protect roots against osmotic stress in the environment. In addition to both the changes in life style and energy metabolism, phytohormons, and osmoprotectants were also found to play a key role in stress protection.
Highlights
Crop cultivation in salinated soils is one of the major challenges facing agriculture today
While the species S. maltophilia has become important as a nosocomial human pathogen, no pathogenic potential for humans has ever been observed in the related species S. rhizophila (Wolf et al, 2002)
Root exudates were collected from oilseed rape cultivar Californium (Kwizda, Austria) and grown for 14 days in gnotobiotic systems of 50 ml of sterilized vermiculite packaged in pots and covered with lids (Metro, Austria)
Summary
Crop cultivation in salinated soils is one of the major challenges facing agriculture today. While the species S. maltophilia has become important as a nosocomial human pathogen, no pathogenic potential for humans has ever been observed in the related species S. rhizophila (Wolf et al, 2002) Both species can be distinguished by the production of the osmoprotective substance glucosylglycerol (GG) (only present in S. rhizophila) and the occurrence of specific multidrug-efflux pumps (only present in S. maltophilia) (Ribbeck-Busch et al, 2005). Use of classical physiological and biochemical methods unveiled the mechanisms of plant growth promotion and biocontrol against soil-borne pathogens (Berg and Ballin, 1994; Kobayashi et al, 1995; Jacobi et al, 1996; Dunne et al, 2000; Suckstorff and Berg, 2003) as well as the production of high amounts of osmolytes trehalose and GG in response to salt stress (Roder et al, 2005).
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