In a new study published on Feb 10th in Nature Plants, a research group led by Prof. CHEN Zhiduan from the Institute of Botany of the Chinese Academy of Sciences, in collaboration with scientists from Fairy Lake Botanical Garden, Fujian Agriculture and Forestry University and Ghent University, have made a great progress in understanding the strategy of plant colonization through analyzing the first high-quality hornwort genome.
Hornwort is a member of the bryophytes family, which are often referred to as the early land plants marking the transition from freshwater to a terrestrial ecosystem. The origin of land plants and the timing of the conquest of land have been contentious for a long time.
In this context, hornworts have been the focus of much attention, since they exhibit traits linking them to algae, have unique associations with cyanobacteria and may be reminiscent of some early and now extinct lineages of early land plants.
Until now, hornworts are the only lineage of land plants without a high-quality reference genome among all important lineages (bryophytes and streptophyte algae) for the point of plant colonization.
The hornwort-genome sequencing project started since 2008. Following more than 10 years of unremitting efforts involving international collaborations, they completed the assembly and annotation of the genome of the hornwort Anthoceros angustus.
The Anthoceros genome is estimated to be composed of 119 Mb, and hence may be among the smallest among land plants.
According to the scientists, phylogenomic inferences confirms the monophyly of bryophytes, with hornworts sister to liverworts and mosses. The simple morphology of hornworts correlates with low genetic redundancy in plant body plan while the basic transcriptional regulation toolkit for plant development has already been established in this early land plant lineage.
In contrast to the ‘light-load’ plant body plan, the Anthoceros genome is characterized by tandem duplication mediated expansion of various gene families, including those related to RNA editing, UV protection and desiccation tolerance, and by acquisition via horizontal gene transfers from soil bacteria and fungi of genes operating in stress response and metabolic pathways.
The latter strategy of 'stolen genes from soil bacteria and fungi' would be common for early land plants, and even streptophyte algae. Before then, hornworts are the only bryophyte clade without high quality reference genome, this study fills the gap, and provides insight into the unique features of hornworts and their molecular adaptations to live on land.
The research was supported by the Chinese Academy of Sciences, the National Natural Science Foundation of China, the Shenzhen Fairy Lake Botanical Garden and Fujian Agriculture and Forestry University.
Comparative genomic analysis of Anthoceros angustus and other 18 plant species. (Image by IBCAS)
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