Laboratoire de Recherche en Sciences Végétales (LRSV), Université de Toulouse, CNRS, UPS, INP, Toulouse, 31320, Castanet-Tolosan, France.
Senckenberg Biodiversity and Climate Research Centre (SBiK-F), Senckenberganlage 25, 60325, Frankfurt am Main, Germany.
Nat Commun. 2024 May 24;15(1):4452. doi: 10.1038/s41467-024-48787-z.
Mutualistic symbioses have contributed to major transitions in the evolution of life. Here, we investigate the evolutionary history and the molecular innovations at the origin of lichens, which are a symbiosis established between fungi and green algae or cyanobacteria. We de novo sequence the genomes or transcriptomes of 12 lichen algal symbiont (LAS) and closely related non-symbiotic algae (NSA) to improve the genomic coverage of Chlorophyte algae. We then perform ancestral state reconstruction and comparative phylogenomics. We identify at least three independent gains of the ability to engage in the lichen symbiosis, one in Trebouxiophyceae and two in Ulvophyceae, confirming the convergent evolution of the lichen symbioses. A carbohydrate-active enzyme from the glycoside hydrolase 8 (GH8) family was identified as a top candidate for the molecular-mechanism underlying lichen symbiosis in Trebouxiophyceae. This GH8 was acquired in lichenizing Trebouxiophyceae by horizontal gene transfer, concomitantly with the ability to associate with lichens fungal symbionts (LFS) and is able to degrade polysaccharides found in the cell wall of LFS. These findings indicate that a combination of gene family expansion and horizontal gene transfer provided the basis for lichenization to evolve in chlorophyte algae.
互利共生关系促进了生命进化的重大转变。在这里，我们研究了地衣的进化历史和起源的分子创新，地衣是真菌和绿藻或蓝藻之间建立的共生关系。我们从头测序了 12 种地衣藻类共生体（LAS）和密切相关的非共生藻类（NSA）的基因组或转录组，以提高绿藻的基因组覆盖率。然后，我们进行了祖先状态重建和比较系统发生基因组学分析。我们确定了至少有三种独立获得参与地衣共生关系的能力，一种在绿藻门中，两种在绿藻门中，证实了地衣共生关系的趋同进化。从糖苷水解酶 8（GH8）家族中鉴定出一种碳水化合物活性酶，它是绿藻门地衣共生关系的分子机制的最佳候选酶。这种 GH8 通过水平基因转移在与地衣共生的绿藻门中获得，同时具有与地衣真菌共生体（LFS）相关联的能力，并能够降解 LFS 细胞壁中发现的多糖。这些发现表明，基因家族扩张和水平基因转移的结合为绿藻门中地衣化的进化提供了基础。
