Dipp Alvarez, M. | Search bioRxiv

bioRxiv2026

Subnuclear cofactor partitioning underlies auxin-dependent transcriptional regulation

Cellular and organismal function relies on the precise activation and repression of gene expression by DNA-binding transcription factors (TFs). Many TFs occur in large gene families, and a key question in biology is how divergent functions emerge in TF families during evolution. Here we discover the biochemical mechanism for transcriptional activation by the Marchantia polymorpha AUXIN RESPONSE FACTOR1 (MpARF1) TF, which relies on direct recruitment of the Mediator complex into subnuclear MpARF1 clusters. We find that the Mediator recruitment region was the evolutionary innovation that converted ARF repressors into activators, switching binding specificity from co-repressor to co-activator. We demonstrate that this evolutionary innovation can be recreated, thereby revealing a deeply conserved mechanism based on competition between ARF clusters at the heart of the transcriptional auxin response.

plant biology↗

bioRxiv2024

Analysis of auxin responses in the fern Ceratopteris richardii identifies tissue ontogeny as a major determinant for response properties

The auxin signalling molecule regulates a range of plant growth and developmental processes. The core transcriptional machinery responsible for auxin-mediated responses is conserved across all land plants. Genetic, physiological and molecular exploration in bryophyte and angiosperm model species have shown both qualitative and quantitative differences in auxin responses. Given the highly divergent ontogeny of the dominant gametophyte (bryophytes) and sporophyte (angiosperms) generations, however, it is unclear whether such differences derive from distinct phylogeny or ontogeny. Here, we address this question by comparing a range of physiological, developmental and molecular responses to auxin in both generations of the model fern Ceratopteris richardii. We find that auxin response in Ceratopteris gametophytes closely resembles that of a thalloid bryophyte, whereas the sporophyte mimics auxin response in flowering plants. This resemblance manifests both at phenotypic and transcriptional level. Furthermore, we show that disrupting auxin transport can lead to ectopic sporophyte induction on the gametophyte, suggesting a role for auxin in the alternation of generations. Our study thus identifies ontogeny, rather than phylogeny, as a major determinant of auxin response properties in land plants. Summary statementStudies in angiosperms and bryophytes have left unresolved the roles of tissue ontogeny and species phylogeny in auxin response. We address that problem by characterizing auxin response in a fern.

plant biology↗