Mistral Seminar

Campus Montpellier SupAgro/INRA de La Gaillarde (2, place P. Viala Montpellier)

Monday, July 8, 2024 at 3 p.m. – Amphi 208 (Cœur d’École)

Peng Yu
Emmy Noether Group Root Functional Biology, Institute of Crop Science and Resource Conservation (INRES), University of Bonn, 53113 Bonn, Germany

Establishment and function of root system and its associated microbiome in maize

The spread of crops and expansion of cultivation from their ancestral habitats were accompanied by substantial phenotypic changes driven by a combination of direct farmer selection and environmental adaptation. Root system function is instrumental in colonizing new habitats and acquiring resources, in particular water and nutrients in natural soils of different geographical origin. During domestication and diversification, the maize root system has become more complex by acquiring the capacity to form seminal roots, a feature largely absent in the maize progenitor teosinte. Nevertheless, the question of how the maize root system adapted its form and function during domestication and global expansion remains elusive. However, understanding the genetic basis, environmental drivers and the potential adaptive value of seminal root number variation to changing environments is essential to develop crops resilient to future climatic challenges.
In the first part of my talk, I will present an 8-year project that we characterized the root systems of >9,000 global maize accessions and its wild relatives, defining the geographical signature and genomic basis of variation in seminal root number. We demonstrated that seminal root number has increased during maize domestication followed by a decrease to limited water availability in locally adapted varieties. By combining environmental and phenotypic association analyses with linkage mapping, we identified genes linking environmental variation and seminal root number. Functional characterization of the transcription factor ZmHb77 and in silico root modelling provides evidence that reshaping root system architecture by reducing the number of seminal roots and promoting lateral root density is beneficial for the resilience of maize seedlings to drought.

However, roots are not alone in the soil but surrounded by a collection of microorganisms i.e. microbiome in a particular habitat. Beneficial interactions with microorganisms are pivotal for crop performance and resilience. Nevertheless, it remains unclear how heritable the microbiome is with respect to the host plant genotype and to what extent host genetic mechanisms can modulate plant-microbiota interactions in the face of environmental stresses.

In the second part of my talk, I will present a large-scale investigation of 3,168 root and rhizosphere microbiome samples from 129 accessions of locally adapted Zea, sourced from diverse habitats and grown under control and different stress conditions. We quantified stress treatment and host genotype effects on the microbiome. Plant genotype and source environment were predictive of microbiome abundance. Genome wide association analysis identified host genetic variants linked to both rhizosphere microbiome abundance and source environment. We identified transposon insertions in a candidate gene linked to both the abundance of a keystone bacterium Massilia in our controlled experiments and total soil nitrogen at source environment. Isolation and controlled inoculation of Massilia alone can contribute to root development, whole plant biomass production and adaptation to low nitrogen availability. We conclude that locally adapted maize varieties exert patterns of genetic control on their root and rhizosphere microbiomes that follow variation in their home environments, consistent with a role in tolerance to prevailing stress.