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Unlocking the Secrets of the Rhizosphere

2016; Elsevier BV; Volume: 21; Issue: 3 Linguagem: Inglês

10.1016/j.tplants.2016.01.020

1878-4372

Susanne Brink,

Composting and Vermicomposting Techniques

This special issue offers an insightful and wide-ranging set of reviews on one of the fastest-growing areas of plant science today, the rhizosphere (Figure 1). The underground world of the rhizosphere, a narrow region of soil surrounding the plant roots, is a concept that was first coined by Lorenz Hiltner in 1904. Hiltner proposed that the rhizosphere is the site of unique interactions between beneficial and pathogenic microorganisms attracted by root exudates. He was a pioneer in microbial ecology with far-reaching views, such as the idea that plant product quality as well as pathogenesis resistance are dependent on the root microflora composition (for more details on Hiltner's life and work, see [1Hartmann A. et al.Lorenz Hiltner, a pioneer in rhizosphere microbial ecology and soil bacteriology research.Plant Soil. 2008; 312: 7-14Crossref Scopus (327) Google Scholar]). The centenary of Hiltner's proposal, which saw the launch of a new series of Rhizosphere conferences, was not simply a reminder of a historical event, but proof that the rhizosphere concept was still very much alive in 2004 and, in fact, has been gaining momentum since. In 2015, Rhizosphere 4 (http://www.rhizo4.org/) was going strong and continued to 'provide a multidisciplinary forum for exchanging innovative ideas and methods for studying the rhizosphere and understanding its complexity and its role in both natural and agricultural ecosystem processes'. This special issue is based on papers presented at Rhizosphere 4, but due to space constraints not all aspects of the rhizosphere could be covered. The emphasis here is on the technological advances (i.e., metagenomics) that have allowed us to gain a better understanding of the shaping of the rhizosphere microbiome (e.g., how the plant selects the rhizo-microbiome and, most importantly, the beneficial microbial partners) and how these insights might be exploited through engineering the rhizosphere with the aim of a sustainable and more ecofriendly agriculture. The importance of the rhizo-microbiome for the functioning of plants has been recognised for decades but, until recently, the tools for investigating many of the interactions were not available. However, increased affordability and power of DNA-sequencing technologies has led to an explosion of large-scale sequencing studies exploring environmental and host-associated microbiomes. For example, the recent characterisation of the Arabidopsis thaliana core microbiome has set the first milestone in providing a tool to unravel the role of the plant in the rhizo-microbiome [2Lundberg D.S. et al.Defining the core Arabidopsis thaliana root microbiome.Nature. 2012; 488: 86-90Crossref PubMed Scopus (1638) Google Scholar]. With it, the vision of the plant and its associated microbial cortege is changing fast; no longer are these two seen as separate entities, but rather as constituents of a superorganism, the holobiont. In these superorganisms, the rhizosphere (including the microbiome) is just one part of a vast, highly complex network of molecular interactions. A set of sophisticated modern technologies (metabolic and molecular genetic methods) have been instrumental in unravelling the various interactions both in these superorganisms and with their environment, and are reviewed in this issue. For 50 years following its inception in 1904, the rhizosphere concept lay dormant, and, although researchers began to appreciate its importance more in the following 50 years, it was not part of Norman Borlaug's green revolution of the late 1960s. However, the rhizosphere concept has now very much taken up a prime spot in plant science research and the future is bright. As discussed in this issue, beneficial microbes can induce plant growth by modifying root development, and understanding these complex cross-kingdom interactions increases our knowledge of root developmental biology and bacterial signalling. Ultimately, this knowledge will foster development of sustainable plant growth-promoting technologies that have the potential to dramatically increase crop yield and food security. In fact, the potential for application in the field has not passed by major industries in the agricultural sector, which are spending millions of dollars annually on the use of plant growth-promoting rhizobacteria (PGPR). Recent advances in metabolomics have made it possible to better understand the chemical dialogue between plants and soil biota, but some challenges remain, such as the sensitivity of the metabolomics platforms and the multivariate data analysis needed to identify causal relations. Therefore, designing measuring techniques capable of resolving processes on a range of scales to unlock the interlinked multicomponent complexity of the rhizosphere will be important. This could help with efforts to engineer components of the rhizosphere (plants and microbes) to promote plant health and growth. Ultimately, there is now a real possibility that the rhizo-microbiome will have an important role in the next green revolution and contribute towards a sustainable and more ecofriendly agriculture by helping to reduce, or even replace, excess pesticide use and the use of fossil-based nitrogen fertilisers. Finally, I would like to thank Rene Geurts for providing many of the article ideas; I am also grateful to all authors and reviewers who participated in this project and were instrumental for producing this exciting special issue. I hope that you will enjoy reading the content and I welcome your comments, ideas, or questions at [email protected]