Coauthored by Isabel Gerhardt*, Rafael Soares Correa de Souza* and Paula Drummond de Castro*

It was a sunny day in March 2017, when the dry season began on the mountain tops in the rupestrian grasslands (campos rupestres) in the Espinhaço Range, southeast of Brazil. We had been walking the whole day and carrying heavy samples of stones, soil, roots, plants and ten kilograms of ice! A long hike back to the car awaited us, and then we could finally rest. Across the unpeopled landscape covered by low vegetation, rocks, and isolated trees, tiny rolling, slippery stones challenged our progress. In our backpacks there were hammers and hoes, unconventional tools for a group of molecular geneticists. This scene would be repeated at least twice a year for two more years.

The motivation for this atypical situation was to understand one aspect of the campos rupestres that had never been explored before: its plant- and soil-associated microbiome.

The flora of the campos rupestres is highly adapted to this unique environment, which includes high sunlight exposure, an extended dry season that lasts almost five months, and additional extreme conditions caused by rocky, shallow soils, and low availability of nutrients, especially phosphorus. The campos rupestres have one of the most P-impoverished soils in the world. Plants in this environment display a range of mechanisms to cope with harsh conditions, which allow them to grow on nutrient-poor shallow soils or even directly on exposed rocks.

Despite the central role played by microorganisms in modulating plant response to stressful conditions, most studies in the campos rupestres have focused on the plant side, by mainly investigating the plant morpho-physiological traits involved in stresses resistance. The GCCRC (Genomics for Climate Change Research Center) – a joint initiative between University of Campinas, Unicamp, and the Brazilian Agricultural Research Corporation, Embrapa - has a great deal of interest in studying plant-associated microbiomes with an ultimately applied focus to identify microorganisms capable of contributing to mitigate the negative effects of abiotic stresses on plant yield. Together with the Laboratory of Plant Functional Ecology(Unicamp) we undertook the challenge of investigating the Velloziaceae-associated microbiome and how it could contribute to the understanding of plant survival in limited environments. The Joint Genome Institute was also a strategic partner who carried out the profiling of the microbial community and the metagenome sequencing.

We decided to investigate the Velloziaceae family since it figures among the ten most species-rich families in the campos rupestres, has its center of diversity in this ecoregion, and is expected to have developed efficient strategies to cope with harsh environmental conditions. Our target was the microbiome associated to Barbacenia macrantha and Vellozia epidendroides, species that grow in contrasting substrates such as exposed rocks and soil patches, respectively. In addition, they do not exhibit mycorrhizal association, which raises the question whether other microbial associations are beneficial to promote plant development.

We have also analyzed the microbiome of soils and rocks in which both species grow. We found the prevalence of a great amount of unknown fungi and bacteria. These results opened an avenue of new questions: Could the microbial community improve plant phosphorus uptake or increase plant growth under limited water availability? How? Which genes may be involved? Can we develop microbiome-based approaches to improve the growth of agricultural crop species under climate change threat?

Through the paper "Microbiomes of Velloziaceae from phosphorus-impoverished soils of the campos rupestres, a biodiversity hotspot" (Camargo et al, 2019) we brought an additional layer on the comprehension of the different levels of biological complexity that are involved and regulate plant responses to abiotic stresses, by investigating the functional and phylogenetic diversity of the plant- and soil-associated microbiome of the campos rupestres, a biodiversity hotspot.

With this study, we also expect to draw attention to a megadiverse, threatened environment that requires further conservation efforts.

(*) GCCRC - Genomics for Climate Change Research Center, Brazil