David M Johnston-Monje: Studying maize microbiomes to discover beneficial endophytic bacteria, elucidate the provenance of microbial populations and develop products for the agricultural industry

Special Seminar

  • Datum: 27.09.2018
  • Uhrzeit: 11:15 - 12:15
  • Vortragende(r): David M Johnston-Monje
  • Max Planck Tandem Group Leader in Plant Architecture and Microbial Ecology, Universidad del Valle, Colombia
  • Ort: MPIPZ
  • Raum: Lecture hall
  • Gastgeber: Paul Schulze-Lefert
David M Johnston-Monje: Studying maize microbiomes to discover beneficial endophytic bacteria, elucidate the provenance of microbial populations and develop products for the agricultural industry
Endophytes are organisms that live inside plants without causing disease and include microbes that benefit their hosts by aiding in nutrient acquisition, growth promotion and disease control. Over millions of years, these microbes have coevolved with their plant hosts, until human domestication, breeding and dispersal to new environments may have altered these relationships. My studies have focused on endophytes in plants of the genus Zea, including modern maize (Zea mays L.), which beginning 9,000 years ago, was domesticated from wild grasses in Mexico, bred into diverse landraces by native peoples and moved to new soils around the world. In an attempt to discover whether domestication and breeding has altered the plant’s microbiome, I surveyed the bacterial endophytes that inhabit seeds of 14 diverse wild, ancient and modern Zea genotypes. To understand whether dispersal to different environments had altered the microbiome, I conducted 2 experiments: in the first, three extreme Zea genotypes, ancestral, intermediate and modern, were grown side by side on two different soils that span the tropical-to-temperate migration route of maize and surveyed their resulting endophytic populations, while in the second experiment, intermediate and modern varieties of Brazilian maize were grown on different soils to study the effects on rhizosphere populations of bacteria. Microbial populations from seeds, roots, shoots and rhizospheres were DNA fingerprinted using next generation sequencing (rhizosphere only) and terminal restriction length polymorphism (TRFLP) of 16S rDNA. To understand microbial functions, bacteria were cultured and tested for >13 in vitro traits including nitrogen fixation, phosphate solubilization, plant hormone production and antibiosis. The results show that different plant tissues and genotypes contain distinct endophytic communities. The community composition of seed endophytes correlated with host phylogeny suggesting that as humans bred maize, they have also inadvertently impacted its microbial inhabitants. Soil swapping and growth on sterile sand confirmed that both root and rhizosphere populations of bacteria in juvenile Zea plants are primarily inherited from the seed, rather than from the soil, and because some bacterial groups were conserved across all plant genotypes and soils, it appears that Zea plants possess a core population of endophytic microbiota. If maize is indeed able to carry most of its microbiota inside/on its seed, this suggests that Zea plants are significantly buffered against microbiome loss during migration. A few strains of isolated bacteria also possessed potentially useful traits such as the ability to enhance plant growth or control plant pathogens, which suggests a target for positive selection that may have encouraged this form of microbial transmission to evolve. My discovery that seed transmission is important for the maize microbiome and that some of these bacteria have the potential for aiding in plant growth was turned into 9 patents and the founding idea behind the world’s most financially successful agricultural startup company. Some challenges and observations on the translation of this microbial technology into products for improving plant agriculture will be discussed.
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