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Some soil bacteria can help plants to combat drought

Rhizobacteria play an important role in the life of plants.  A study carried out in Montpellier has shown how they exert a protective effect against drought, enabling a reduction of up to 50% in plant mortality in the event of extreme water stress.

An arm of the Phenopsis robot, at the plant phenotyping platform in Montpellier, which makes it possible to weigh, irrigate and acquire images of more than 500 plants in strictly controlled environmental conditions. © INRA
By Denis Vile - Pascale Mollier, translated by Vicky Hawken
Updated on 03/17/2014
Published on 03/05/2014

Bacteria in contact with plant roots

Rhizobacteria grouped under the term "plant growth-promoting rhizobacteria", or PGPR, are a subject of increasing interest in agronomy.  Indeed, these soil bacteria are able to interact with the root systems of plants and improve their productivity.  In some cases, they may also increase plant resistance to biotic and abiotic stresses such as water stress.  One of these organisms, Phyllobacterium brassicacearum, has been isolated in the rhizosphere of French rapeseed crops, and the STM196 strain proved to be the most effective in stimulating the growth of this cultivated species.

Protection against drought: coordinated mechanisms

An integrative biology technique developed by the Contract-based Research Unit for Tropical and Mediterranean Symbioses (USC LSTM) (1) using P. brassicacearum and A. thaliana has enabled the identification of original mechanisms and molecular actors involved in in vitro PGPR-plant interactions. Thanks to the Phenopsis phenotyping platform (2), a refined and detailed analysis of the effects of P. brassicacearum STM196 on the growth and physiology of A. thaliana was carried out under quantified and controlled conditions of water stress (3). This analysis showed that a delay in the reproductive development of plants inoculated with strain STM196 induced an increase in the production of plant biomass, independent of the irrigation conditions.  In addition, the inoculated plants displayed a better tolerance of moderate water stress, illustrated by a 50% gain in biomass.  Inoculation with STM196 induced a coordinated modification of physiological mechanisms which all tended towards an optimisation of soil water uptake and a reduction in water loss from the leaves.  Indeed, the presence of this bacterium was associated with an increase in the root system, thus permitting greater exploration of the soil.  STM196 also caused a reduction in water losses by transpiration, probably following the closure of stomata because of a rise in the abscissic acid content of the leaves (4). Findings that are currently being evaluated have also shown that in the context of more severe water stress causing high plant mortality rates (60%), inoculation with strain STM196 enabled a remarkable improvement in survival (30% of mortality) through a better tolerance of dehydration (5).

Inoculation with STM196 thus represents an added value in strategies for stress resistance and the management of intrinsic resources by plants.  These results highlight the importance of plant-bacteria interactions to the responses of plants to drought, and offer new research pathways to improve the drought tolerance of crops.

Bibliography:

(1) Kechid M. et al. 2013. The NRT2.5 and NRT2.6 genes are involved in growth promotion of Arabidopsis by the plant growth-promoting rhizobacterium (PGPR) strain Phyllobacterium brassicacearum STM196.New Phytol.,198(2): 514-524.

(2) Granier C. et al. 2006. PHENOPSIS, an automated platform for reproducible phenotyping of plant responses to soil water deficit in Arabidopsis thaliana permitted the identification of an accession with low sensitivity to soil water deficit. New Phytol,169(3): 623-635.

(3) Bresson J. et al. 2013. The PGPR strain Phyllobacterium brassicacearum STM196 induces a reproductive delay and physiological changes that result in improved drought tolerance in Arabidopsis. New Phytol.,200(2): 558-569.

(4) Pantin F. et al. 2013. Developmental riming of stomatal sensitivity to abscisic acid by leaf microclimate. Curr. Biol.,23(18): 1805–1811.

(5) Bresson J. 2013. Plant-microorganisms interactions : Implication of the rhizobacteria Phyllobacterium brassicacearum in Arabidopsis thaliana responses to water deficit. PhD thesis, Université Montpellier II.

Contact(s)
Scientific contact(s):

  • Denis Vile Joint Research Unit for Ecophysiology of Plants under Environmental Stress (INRA-Montpellier Supagro)
Associated Division(s):
Environment and Agronomy
Associated Centre(s):
Montpellier

Reference

Bresson J, Varoquaux F, Bontpart T, Touraine B, Vile D. 2013. The PGPR strain Phyllobacterium brassicacearum STM196 induces a reproductive delay and physiological changes that result in improved drought tolerance in Arabidopsis. New Phytologist,200(2): 558-569. Published online on 4 July 2013.

Rhizobacteria-plants: reciprocal benefits

Rhizobacteria are symbiotic or non-symbiotic bacteria which display an ability to intensively colonise the roots of plants.  Development of these bacteria in the root environment (rhizosphere) is favoured by the root exsudates released by the plant: organic carbon and nitrogen substances such as polysaccharides, organic acids and proteins, which serve as nutrients for the bacteria.  In return, the rhizobacteria influence soil-plant exchanges, which increase in line with their density and activity.

Platforms for the high-throughput study of plant behaviour

The Joint Research Unit for the Ecophysiology of Plants under Environmental Stress in Montpellier (which is one of the three units which form the Institute for Integrative Plant Biology) manages three high-throughput phenotyping platforms, grouped under the name of M3P:

  • Phenodyn, which enables the simultaneous monitoring of leaf extension and transpiration in 450 plants under controlled climatic conditions;
  • Phenopsis, which can monitor the growth of more than 3x500 plants of Arabidopsis thaliana under individually-programmed soil water levels;
  • Phenoarch, which enables simultaneous monitoring of the leaf growth and architecture of 1650 plants at a rate compatible with genomic selection (which consists in establishing statistical correlations between the nucleotide sequences and the phenotypic traits of plants).

These facilities provide access to, and the study of, the expression of genes and their functions at different organisational levels - from the cell to the whole plant - under controlled environmental conditions.