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Apr. 24, 2009 Research Highlight Biology

Networking for survival

A metabolic study reveals that plant-based compounds cooperate to overcome dehydration

Schematic of dehydration stress response in Arabidopsis Figure 1: Metabolic networking in response to dehydration stress in Arabidopsis. The metabolic network analysis revealed that dehydration-increased amino acids (red dots) contribute more significantly to the dehydration-stress response when they have a global correlation with each other (pink area), whereas sugars show a modest network that is independent of amino acids (blue area). (blue dots, dehydration-decreased metabolites; yellow dots, metabolites with no change, pairs show significantly correlated metabolites)

Japanese plant biologists have exposed dynamic networks of small molecules that respond to dehydration stress in plants. Worldwide, drought is a major limitation to crop productivity, which results in economic loss and food shortages.

The researchers, led by Kazuo Shinozaki of the RIKEN Plant Science Center in Tsukuba, analyzed the so-called dehydration metabolome, which includes the complete set of small molecules, or metabolites, in drought-stressed examples of the model plant Arabidopsis thaliana. Metabolomics is a powerful tool for understanding highly complex cellular processes. Using this approach, the researchers found that networks of metabolites interact in adaptation to dry conditions. Their results are published in The Plant Journal 1.

Abscisic acid (ABA) is a phytohormone that plays a prominent role in regulating the dehydration response. Shinozaki and colleagues investigated its effect on metabolic changes in response to drought by working with a genetic mutant of Arabidopsis, nc3-2 in which ABA accumulation is significantly reduced. They found that an increased rate of accumulation of metabolites such as amino acids in response to a lack of water is dependent on ABA, and depletion of this hormone alters metabolite concentrations.

The team found that dehydration-increased amino acids in wild-type plants correlated with each other, and that this interaction contributed significantly to the stress response. This suggests that metabolic engineering of amino acid biosynthesis is a promising approach for improving drought tolerance. Sugars showed no correlations with amino acid groups but did interact with each other, demonstrating for the first time that these two types of metabolite respond to dehydration stress through different metabolic networks (Fig. 1).

Shinozaki and colleagues showed that nc3-2 metabolites had to interact more widely than those in wild-type plants. Despite having lower dehydration-induced metabolite concentrations than wild-type plants, ABA-deficient mutants adapted somewhat to dry conditions through extensive correlation between certain sugars and other small molecules.

The study has revealed many more ABA-dependent metabolites and metabolic pathways than previously reported. “Soon, combining mathematics, computational biology and molecular biology should provide more insight into the complex metabolic networks that constitute the response to dehydration stress,” says team-member Kaoru Urano. Understanding the sophisticated interactions between metabolites in dehydrated plants will ultimately enable better management of crops in harsh environments.

References

  • 1. Urano, K., Maruyama, K., Ogata, Y., Morishita, Y., Takeda, M., Sakurai, N., Suzuki, H. Saito, K., Shibata, D., Kobayashi, M., et al. Characterization of the ABA-regulated global responses to dehydration in Arabidopsis by metabolomics. The Plant Journal 57, 1065–1078 (2009). doi: 10.1111/j.1365-313X.2008.03748.x

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