Rôles des strigolactones et évolution des compétences mycorhiziennes dans la lignée verte

La lignée verte comprend les algues vertes et les plantes terrestres. Grâce à une association symbiotique avec des champignons Gloméromycètes, la symbiose mycorhizienne à arbuscules, les plantes terrestres ont pu s'adapter plus facilement à leurs nouvelles conditions de vie. Cette symbiose se met en place grâce à des échanges de signaux entre les partenaires. Ainsi, dans les stades précoces une famille de petites molécules produites par les plantes, les strigolactones, stimulent de façon remarquable le développement du champignon. Ces molécules sont par ailleurs connues chez les Angiospermes comme régulateur hormonal de la ramification des tiges. Nous nous sommes posé la question de savoir quand les strigolactones étaient apparues au cours de l'évolution des plantes et quelles étaient alors leurs fonctions primitives. Nous avons pu montrer que les strigolactones étaient apparues avec les Charales et qu'elles étaient conservées chez les Hépatiques, les descendantes des premières plantes terrestres. Nous avons découvert qu'un apport exogène de strigolactones, pouvait stimuler la croissance des rhizoïdes d'une Hépatique et d'une Mousse. Nous avons également montré que les strigolactones participaient au contrôle de la formation des racines latérales et des poils absorbant chez Arabidopsis thaliana. Notre hypothèse est que les fonctions primitives des strigolactones étaient de stimuler le développement des rhizoïdes chez les premières plantes terrestres, puis de promouvoir la symbiose mycorhizienne à arbuscules, deux fonctions primordiales pour la conquête du monde terrestre. Plus tardivement, avec l'apparition des angiospermes, l'activité sur les rhizoïdes a pu être recrutée pour contrôler l'élongation des poils absorbants. Puis les strigolactones ont acquis de nouvelles fonctions comme celles de contrôler la ramification des racines et des tiges. Enfin, nous proposons un schéma plus global montrant l'évolution étape par étape des acteurs moléculaires de la régulation de l'établissement de la symbiose endomycorhizienne à arbuscule tout au long de la lignée verte.The green lineage comprises green algae and land plants. With the symbiotic association with fungi, the Glomeromycota, land plants have been more easily adapted to their new environment. The establishment of this arbuscular mycorrhizal (AM) symbiosis involved the exchange of signals between both partners. Thus, in early stage, a family of small secondary metabolites produce by plant roots, the strigolactones, strongly stimulate fungi development. In Angiosperms, these molecules act also as hormonal regulator of shoot branching. We asked the question of the appearance of the strigolactones during plants evolution and of their primitive role. We shown that strigolactones appeared with Charales, one of the closest green algae relative to land plants, and are conserved in liverworts, the most basal land plants. We discovered that GR24, an analogous of strigolactones, stimulate rhizoids growth of a liverwort and a moss. We also shown that strigolactones participate in the development of lateral roots and in the growth of root hairs in the model Angiosperm Arabidopsis thaliana. We hypothetised that the primitive function of strigolactones was to stimulate rhizoids development of the first land plants and to facilitate the interaction with AM fungi, two crucial functions for land conquest by plants. Latter, with Angiosperms appearance, the activity on rhizoids could have been recruited to control root hairs elongation, which are cells related to rhizoids. In Angiosperms, strigolactones acquired new functions like the control of root and shoot branching. To finish, we proposed a more complete scheme of the evolution of the AM symbiosis molecular regulators throughout the green lineage

10KP: A phylodiverse genome sequencing plan.

Understanding plant evolution and diversity in a phylogenomic context is an enormous challenge due, in part, to limited availability of genome-scale data across phylodiverse species. The 10KP (10,000 Plants) Genome Sequencing Project will sequence and characterize representative genomes from every major clade of embryophytes, green algae, and protists (excluding fungi) within the next 5 years. By implementing and continuously improving leading-edge sequencing technologies and bioinformatics tools, 10KP will catalogue the genome content of plant and protist diversity and make these data freely available as an enduring foundation for future scientific discoveries and applications. 10KP is structured as an international consortium, open to the global community, including botanical gardens, plant research institutes, universities, and private industry. Our immediate goal is to establish a policy framework for this endeavor, the principles of which are outlined here

Lipid transfer from plants to arbuscular mycorrhiza fungi

Arbuscular mycorrhiza (AM) symbioses contribute to global carbon cycles as plant hosts divert up to 20% of photosynthate to the obligate biotrophic fungi. Previous studies suggested carbohydrates as the only form of carbon transferred to the fungi. However, de novo fatty acid (FA) synthesis has not been observed in AM fungi in absence of the plant. In a forward genetic approach, we identified two Lotus japonicus mutants defective in AM-specific paralogs of lipid biosynthesis genes (KASI and GPAT6). These mutants perturb fungal development and accumulation of emblematic fungal 16:1 omega 5 FAs. Using isotopolog profiling we demonstrate that C-13 patterns of fungal FAs recapitulate those of wild-type hosts, indicating cross-kingdom lipid transfer from plants to fungi. This transfer of labelled FAs was not observed for the AM-specific lipid biosynthesis mutants. Thus, growth and development of beneficial AM fungi is not only fueled by sugars but depends on lipid transfer from plant hosts

Anthoceros genomes illuminate the origin of land plants and the unique biology of hornworts

Hornworts comprise a bryophyte lineage that diverged from other extant land plants >400 million years ago and bears unique biological features, including a distinct sporophyte architecture, cyanobacterial symbiosis and a pyrenoid-based carbon-concentrating mechanism (CCM). Here, we provide three high-quality genomes of Anthoceros hornworts. Phylogenomic analyses place hornworts as a sister clade to liverworts plus mosses with high support. The Anthoceros genomes lack repeat-dense centromeres as well as whole-genome duplication, and contain a limited transcription factor repertoire. Several genes involved in angiosperm meristem and stomatal function are conserved in Anthoceros and upregulated during sporophyte development, suggesting possible homologies at the genetic level. We identified candidate genes involved in cyanobacterial symbiosis and found that LCIB, a Chlamydomonas CCM gene, is present in hornworts but absent in other plant lineages, implying a possible conserved role in CCM function. We anticipate that these hornwort genomes will serve as essential references for future hornwort research and comparative studies across land plants.</p

Genomes of multicellular algal sisters to land plants illuminate signaling network evolution

Zygnematophyceae are the algal sisters of land plants. Here we sequenced four genomes of filamentous Zygnematophyceae, including chromosome-scale assemblies for three strains of Zygnema circumcarinatum. We inferred traits in the ancestor of Zygnematophyceae and land plants that might have ushered in the conquest of land by plants: expanded genes for signaling cascades, environmental response, and multicellular growth. Zygnematophyceae and land plants share all the major enzymes for cell wall synthesis and remodifications, and gene gains shaped this toolkit. Co-expression network analyses uncover gene cohorts that unite environmental signaling with multicellular developmental programs. Our data shed light on a molecular chassis that balances environmental response and growth modulation across more than 600 million years of streptophyte evolution

Anthoceros genomes illuminate the origin of land plants and the unique biology of hornworts.

Funder: National Institute for Basic Biology (NIBB) Collaborative Research Program (13-710)Funder: The Forschungskredit of the University of Zurich The University Research Priority Program “Evolution in Action” of the University of Zurich The Georges and Antoine Claraz Foundation (Switzerland)Funder: Spanish Ministry of Science, Innovation and Universities (BFU2016-80621-P)Funder: The Georges and Antoine Claraz Foundation (Switzerland) The Research Priority Program “Evolution in Action” of the University of ZurichFunder: Foundation of German Business (sdw), Georges and Antoine Claraz Foundation, URPP Evolution in Action of the University of ZurichFunder: Special Grant for Innovation in Research Program of the Technical University of Dresden (Germany).Hornworts comprise a bryophyte lineage that diverged from other extant land plants >400 million years ago and bears unique biological features, including a distinct sporophyte architecture, cyanobacterial symbiosis and a pyrenoid-based carbon-concentrating mechanism (CCM). Here, we provide three high-quality genomes of Anthoceros hornworts. Phylogenomic analyses place hornworts as a sister clade to liverworts plus mosses with high support. The Anthoceros genomes lack repeat-dense centromeres as well as whole-genome duplication, and contain a limited transcription factor repertoire. Several genes involved in angiosperm meristem and stomatal function are conserved in Anthoceros and upregulated during sporophyte development, suggesting possible homologies at the genetic level. We identified candidate genes involved in cyanobacterial symbiosis and found that LCIB, a Chlamydomonas CCM gene, is present in hornworts but absent in other plant lineages, implying a possible conserved role in CCM function. We anticipate that these hornwort genomes will serve as essential references for future hornwort research and comparative studies across land plants

Fern genomes elucidate land plant evolution and cyanobacterial symbioses

Li F-W, Brouwer P, Carretero-Paulet L, et al. Fern genomes elucidate land plant evolution and cyanobacterial symbioses. NATURE PLANTS. 2018;4(7):460-472

Standards for plant synthetic biology: a common syntax for exchange of DNA parts.

Inventors in the field of mechanical and electronic engineering can access multitudes of components and, thanks to standardization, parts from different manufacturers can be used in combination with each other. The introduction of BioBrick standards for the assembly of characterized DNA sequences was a landmark in microbial engineering, shaping the field of synthetic biology. Here, we describe a standard for Type IIS restriction endonuclease-mediated assembly, defining a common syntax of 12 fusion sites to enable the facile assembly of eukaryotic transcriptional units. This standard has been developed and agreed by representatives and leaders of the international plant science and synthetic biology communities, including inventors, developers and adopters of Type IIS cloning methods. Our vision is of an extensive catalogue of standardized, characterized DNA parts that will accelerate plant bioengineering.Biotechnological and Biological Sciences Research Council (BBSRC). Grant Numbers: BB/K005952/1, BB/L02182X/1 Synthetic Biology Research Centre ‘OpenPlant’ award. Grant Number: BB/L014130/1 Spanish MINECO. Grant Number: BIO2013‐42193‐R Engineering Nitrogen Symbiosis for Africa (ENSA) The Bill & Melinda Gates Foundation US Department of Energy, Office of Biological and Environmental. Grant Number: DE‐AC02‐05CH1123 COST Action. Grant Number: FA100

Comparative phylogenomics of symbiotic associations

International audienceUnderstanding the genetic bases of complex traits has been a main challenge in biology for decades. Comparative phylogenomics offers an opportunity to identify candidate genes associated with these complex traits. This approach initially developed in prokaryotes consists in looking at shared coevolution between genes and traits. It thus requires a precise reconstruction of the trait evolution, a large genomic sampling in the clades of interest and an accurate definition of orthogroups. Recently, with the growing body of sequenced plant genomes, comparative genomics has been successfully applied to plants to study the widespread arbuscular mycorrhizal symbiosis. Here I will use these findings to illustrate the main principles of comparative phylogenomic approaches and propose directions to improve our understanding of symbiotic associations