Abstract
Hornworts, liverworts and mosses are three early diverging clades of land plants, and together comprise the bryophytes. Here, we report the draft genome sequence of the hornwort Anthoceros angustus. Phylogenomic inferences confirm 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. Although the Anthoceros genome is small and characterized by minimal redundancy, expansions are observed in gene families related to RNA editing, UV protection and desiccation tolerance. The genome of A. angustus bears the signatures of horizontally transferred genes from bacteria and fungi, in particular of genes operating in stress-response and metabolic pathways. Our study provides insight into the unique features of hornworts and their molecular adaptations to live on land.
Highlights
Land plants (Embryophyta) probably originated in the early Palaeozoic[1], initiating the colonization of the terrestrial habitat
In addition to protein-coding genes, we identified 30 known mature micro RNAs, 180 novel mature miRNAs, 347 transfer RNAs, 94 ribosomal RNAs and 83 small nuclear RNAs in the A. angustus genome (Supplementary Table 11)
The large number of A. angustus-specific monocupin genes are homologous to the P. patens PpGLP6 gene (XP_001782709.1) (Supplementary Fig. 57 and Supplementary Note 5.2), which encodes a protein with manganese-containing extracellular superoxide dismutase (SOD) activity to respond to oxidative stress in terrestrial environments[45]
Summary
To that of the other two bryophyte genomes (Supplementary Fig. 15, Supplementary Table 21 and Supplementary Note 4.1). In the bHLH family, the class I RSL gene that controls the development of rhizoids and root hairs, thought to have been important for the colonization of land[34], is present in the A. angustus genome, whereas the class II RSL genes responsible for regulating protonema differentiation in P. patens or root hair elongation in A. thaliana by auxin[35] are absent (Supplementary Fig. 27 and Supplementary Note 4.2). Our findings add further support to the hypothesis that an increase in the number of both RNA editing sites and PPR genes (especially the PLS-class PPR) occurred after the separation of land plants from green algae[41,42] (Supplementary Table 23). The large number of A. angustus-specific monocupin genes are homologous to the P. patens PpGLP6 gene (XP_001782709.1) (Supplementary Fig. 57 and Supplementary Note 5.2), which encodes a protein with manganese-containing extracellular superoxide dismutase (SOD) activity to respond to oxidative stress in terrestrial environments[45]. Hoyosella subflava WP_013806789.1 Williamsia muralis WP_062796745.1 Mycobacterium chelonae group WP_057967264.1
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