Deciphering the EVOlution of biopolymers that shape plant apoplastic protective BARriers through the elucidation of underlying metabolic routes – EVOBAR

Land colonization by plants, about 500 million years ago, was one of the most formative evolutionary steps for terraformation. It paved the way for the development of complex terrestrial ecosystems and the emergence of new life forms. Upon transition from water to land, plants have been exposed to new constraints, such as high solar irradiation (UV), drought, and extreme and fluctuating temperatures. The formation of protective apoplastic barriers probably played a key role in this transition by isolating cells from external aggressions, acting as a UV-block and allowing the formation of specialized structures required for water management (e.g. cuticle). In flowering plants, these functions are mainly conferred by four hydrophobic extracellular biopolymers: cutin, suberin, sporopollenin and lignin. The understanding of the biosynthesis of these polymers in flowering plants has considerably progressed in the recent years, but their origin remains poorly understood. Recent data from the study of charophytes (freshwater algae) and bryophytes (earliest land plants) suggest that they have evolved from a common ancestral polymer. The EVOBAR project proposes to reveal the origins of the plant biopolymers shaping protective apoplastic barriers by elucidating the metabolic routes leading to the synthesis of their precursors in a selection of plants recapitulating plant land colonization: the charophytes Klebsormidium nitens and Mesotaenium caldariorum, and bryophytes Marchantia polymorpha and Physcomitrella patens. The project will mainly focus on enzymes of the cytochrome P450 family that are important drivers of plant metabolic diversity and key players in the synthesis of aliphatic and phenolic biopolymer subunits. The project will implement a transdisciplinary approach, based on CRISPR/Cas9-mediated production of mutants of the candidate genes identified by phylogenomics, biochemical characterization of recombinant proteins, extensive metabolic profiling and analysis of wild-type and mutant polymers, as well as on the phenotypic and physiological characterization of plants using the latest techniques of structural and molecular imaging (3D-SEM, MALDI-imaging). Data from the EVOBAR project will help elucidate the evolutionary patterns of the biopolymers forming plant apoplastic barriers and associated metabolic pathways. They will also highlight the properties of the first biopolymers and their impact on the development and environmental resilience of plants, potentially revealing essential adaptations to primordial terrestrial conditions. Since plant apoplastic barriers control important agronomic traits (e.g. cuticle/passive water loss; suberized endoderm/nutrient homeostasis), the project will open avenues for new, evolution-inspired strategies to improve plant resilience in the context of climate change and world population increase. It will also contribute to building a body of fundamental knowledge necessary for the sustainable use of bryophytes and freshwater algae biomass and their bioengineering in a green chemistry approach.