Comparative analysis of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) gene family between bryophytes and seed plants

SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) genes encode plant-specific transcription factors which have been found to be conserved in green plants lineage. SPL proteins are important regulators of diverse plant developmental processes in bryophytes and vascular plants. In our study, we took advantage of available genome sequences of representatives of each bryophyte clade to investigate the relationships of SPL genes between bryophytes and model angiosperm Arabidopsis thaliana. We have identified four SPL genes in each of the two hornworts species, Anthoceros agrestis and Anthoceros punctatus, what is similar to the set of SPL genes present in the liverwort Marchantia polymorpha. Thus, the analyzed hornworts and liverwort genomes encode a minimal set of SPL genes in comparison to other land plants that may resemble an archetype of SPL genes present in the ancestor of land plants. The phylogenetic analysis revealed the presence of four SPL groups. Comparative gene structure analysis showed that SPLs share similar exon-intron organization within the same phylogenetic group with some exceptions in hornworts. While we have identified conserved protein motifs between bryophytes and Arabidopsis in three out of four phylogenetic groups, the motif content differed explicitly in the fourth group. Since current understanding of SPL genes mostly arises from seed plants, the presented comparative and phylogenetic analysis will provide better understanding of SPL gene family from the representatives of the oldest living land plants.