- Integrative analysis of seedling heat stress acclimation
The aim of the ACCLIMHOT project (funded by RFI Objectif Végétal, 2015-2018) is to uncover the roles energy-transducing organelles play in acquired thermotolerance of young seedlings of Arabidopsis. We are using an integrative approach, taking advantage of a robust experimental system we have developed using seedlings grown in liquid medium, and combining physiology, cell biology, metabolomics and transcriptomics. We have already established that preserving the function of mitochondria and chloroplasts following heat stress is crucial for survival, and is thus an essential component of acclimation. The reactivation of mitochondrial dynamics during recovery appears also important. Omics data, which are currently under analysis, will provide a general scheme of how acclimation shape the response of seedlings to an otherwise lethal stress treatment.
- Exploring natural diversity for nitrogen use efficiency during seedling heterotrophic growth under low temperature and nitrogen supply
Our team has been studying for many years the genetic bases of seedling pre-emergence growth under unfavorable environmental conditions. At this stage of development, which usually occurs in the dark, seedlings are still heterotrophic and very sensitive to stress and environmental signals. Although seedling pre-emergence growth is crucial for successful crop establishment, it remains poorly studied in the agronomical context.
In the project MeDi-SENS (funded by RFI Objectif Végétal, 2016-2019), the natural diversity of the model legume Medicago truncatula is explored to highlight physiological adaptive behaviors for nitrogen use efficiency during seedling heterotrophic growth and to identify loci associated to the seedling performance under low temperature (chilling) and low nitrogen supply using a GWAS approach. For this purpose, a core collection of 192 accessions is characterized for elongation of hypocotyl and radicle, allocation of seed biomass to these organs and nitrate uptake. A small panel of genotypes selected to be representative of physiological behaviors is more thoroughly analyzed (e.g. respective contributions of endogenous-seed reserves and exogenous-nitrate source of nitrogen to seedling growth). The results should lead to the identification of physiological traits for ideotype(s) that can fit seedling establishment of crops under low temperature and/or nitrogen supply.
- Cellular bases of hypocotyl pre-emergence growth genotypic differences under cold stress
The study focuses on hypocotyl, the organ pushing epigean seedlings out of the soil. An integrative approach combining genetic and eco-physiology was developed in Medicago truncatula to analyze cellular changes affecting hypocotyl elongation in the dark due to genotype and/or environment (i.e. temperature, water potential). Combining transcriptome and cellular analyses on two contrasting genotypes for hypocotyl growth at low temperature highlighted that hypocotyl elongation only relies on cell elongation in M. truncatula and that epidermal cell number pre-established in the embryo differed between the genotypes (Pierre et al., 2014). Extending the study to a core-collection of 16 accessions showed that hypocotyl epidermal cell number in seeds displays a high genetic variability and is under strong genetic control. However, cell length instead of cell number becomes the predominant factor contributing to hypocotyl length genotypic differences under low temperature and water deficit (Youssef et al., 2016). QTLs controlling epidermal cell number and cell length affecting hypocotyl elongation at low temperature were revealed (Dias et al., 2011; Youssef et al., 2016). We are currently investigating molecular determinants of cell elongation responsible for hypocotyl length genotypic differences. Proteome, cell wall composition, soluble sugar and ROS content are compared between two genotypes sharing a similar cell number but contrasted cell elongation capacity.
- Phenotyping collections of accessions for seedling vigour traits in legumes
UMR IRHS via the Conserto, SMS and ImHorPhen teams, as well as SNES-GEVES, participate to the European project H2020 EUCLEG (2017-2020): Breeding and grain vegetables to increase EU's and China's self-sufficiency protein (http://www.angers-nantes.inra.fr/Toutes-les-actualites/projet-EUCLEG). By using diverse genetic resources and benefiting from advances in molecular tools, EUCLEG aims to identify and develop the best genetic resources, phenotypic methods and molecular tools for selecting forage (alfalfa and red clover) and seed legume (peas, faba beans and soya beans) varieties with improved performance under abiotic stress and in the main regions of Europe and China. Coordinated by the URP3F (INRA Nouvelle-Aquitaine Poitiers), this 4-year project brings together 38 public and private partners in France and in 12 other countries (Europe and China). The IRHS teams and SNES-GEVES are involved in the phenotyping of the establishment of young seedlings, from germination to emergence, in several forage and seed legumes. Thanks to the PHENOTIC platform, genetic variability related to germination, seedling growth (hypocotyl / root) and emergence will be evaluated in different environmental conditions in 400 populations of alfalfa and red clover and 400 pea and soy accessions. Phenotyping data will be used to identify marker-phenotype associations to improve crop establishment and yield in legumes using GWAS approaches.
- Impact of cyto-nuclear adaptation on energy metabolism and seed physiology
A large collaborative project dedicated to multi-scale phenotyping of Arabidopsis cytolines.
We have been involved in the ANR BIOADAPT 2012 Cytopheno project (Coordinated by Françoise Budar, INRA IJPB Versailles), which aims to explore the role of cyto-nuclear co-adaptation by taking advantage of a novel genetic resource consisting of 56 cytolines (lines combining the nuclear genome of one accession with the mitochondrial and plastid genomes of another) produced from a core-collection of eight parental lines. We have contributed in this large collaborative project to the phenotyping of seed germination, respiration and seedling energy transduction for the 64 lines. Disruption of cytonuclear co-adaptation had a strong impact on seed traits such as dormancy, longevity and seed vigor (manuscript submitted). We aim to further characterize the role of cytonuclear co-adaptation in the energy use efficiency of seedlings and leaves using this original genetic resource.