Nitrate-dependent control of root architecture and N nutrition are altered by a plant growth-promoting Phyllobacterium sp

Abstract

Both root architecture and plant N nutrition are altered by inoculation with the plant growth-promoting rhizobacteria (PGPR) Phyllobacterium strain STM196. It is known that NO3- and N metabolites can act as regulatory signals on root development and N transporters. In this study, we investigate the possible interrelated effects on root development and N transport. We show that the inhibition of Arabidopsis lateral root growth by high external NO3- is overridden by Phyllobacterium inoculation. However, the leaf NO3- pool remained unchanged in inoculated plants. By contrast, the Gln root pool was reduced in inoculated plants. Unexpectedly, NO3- influx and the expression levels of AtNRT1.1 and AtNRT2.1 genes coding for root NO3- transporters were also decreased after 8 days of Phyllobacterium inoculation. Although the mechanisms by which PGPR exert their positive effects remain unknown, our data show that they can optimize plant development independently from N supply, thus alleviating the regulatory mechanisms that operate in axenic conditions. In addition, we found that Phyllobacterium sp. elicited a very strong induction of AtNRT2.5 and AtNRT2.6, both genes preferentially expressed in the shoots whose functions are unknown.

Sugarcane growth promotion by Kosakonia sp. ICB117 an endophytic and diazotrophic bacterium

“…The positive effects of these bacteria on the plant are consistent with literature data (Dobbelaere et al, 2003;Mantelin et al, 2006) suggesting that the stimuli to plant growth are always correlated with remarkable changes in root morphology, such as increased length of lateral roots and number of hairs (Mantelin and Touraine, 2004;Vacheron et al, 2013). Several authors attribute the increase in root development in inoculated plants to the release of auxin by bacteria (Bhattacharjee et al, 2008;Dobbelaere et al, 2003;Mantelin and Touraine, 2004).…”

Earthworms influence the production of above- and belowground biomass and the expression of genes involved in cell proliferation and stress responses in Arabidopsis thaliana

“…Compared to those growing in the rich soil, the plants cultivated in the poor soil without earthworms showed phenotypic and developmental responses typical of mineral -particularly nitrogen (N)-deficiency: early reproductive switch, smaller shoot to root ratio, as a result of a higher allocation of assimilates to the roots and severely reduced seed yield (Eaton, 1935;Scheible et al, 1997;Hirai et al, 2004;Hermans et al, 2006;Mantelin et al, 2006;Remans et al, 2006). The almost complete depletion of the initial NO 3 À content in the poor soil by the end of the experiment support the hypothesis of N-starvation.…”

Emended description of the genus Phyllobacterium and description of four novel species associated with plant roots: Phyllobacterium bourgognense sp. nov., Phyllobacterium ifriqiyense sp. nov., Phyllobacterium leguminum sp. nov. and Phyllobacterium brassicacearum sp. nov.

“…Strain W3 stimulates initial root growth and de novo root development in Picea spp. (Chanway et al, 1994), strain STM 196 (a synonym of isolate 29-15) was recognized as a plant-growth-promoting bacterium in plant culture of oilseed rape (Brassica napus) (Bertrand et al, 2001;Larcher et al, 2003) and Arabidopsis thaliana (Mantelin et al, 2006) and strain BOG-1-98 promotes growth of black mangrove seedlings in artificial sea water when co-inoculated with Bacillus licheniformis (Rojas et al, 2001). Interestingly, some strains have been isolated from root nodules (Sturz et al, 1997;Rasolomampianina et al, 2005), although the capacity of the isolates to induce nodulation was not clearly demonstrated.…”