RESUMO
In angiosperms, the phase transition from vegetative to reproductive growth involves the de-repression of the squamosa promoter-binding-protein-like (SPL) class of transcription factors, which is negatively regulated by the specific microRNAs (miRNAs/miRs) miR156/529 [1]. Non-vascular land plants also undergo growth-phase transition to the reproductive state, but knowledge regarding the controlling mechanisms is limited. Here, we investigate the reproductive transition in the liverwort Marchantia polymorpha, focusing on the roles of miR529c [2-4] and MpSPL2. First, we established mir529c-null mutants using CRISPR/Cas9. Even in the absence of far-red light-supplemented long-day condition, which is usually needed to induce reproductive development [5, 6], the mutant thalli developed sexual reproductive organs (gametangia) and produced gametes. Transgenic plants expressing a miR529-resistant MpSPL2 transgene also showed a similar phenotype of reproductive transition in the absence of inductive far-red light signals. In these mutants and transgenic plants, the MpSPL2 mRNA abundance was elevated. Mpspl2ko mutant plants showed successful gamete development and fertilization, which suggests that MpSPL2 is involved in, but not essential for, sexual reproduction in M. polymorpha. Furthermore, analysis of Mpspl2ko mutant and its complemented lines suggests that MpSPL2 may have a role in promotion of reproductive transition. These findings support the notion that the transition to reproductive development in liverworts is controlled by a system similar to that in angiosperms, and the miR156/529-SPL module has common significance in the control of the vegetative-to-reproductive transition during development in many land plants, including liverworts.
Assuntos
Marchantia/fisiologia , MicroRNAs/genética , Proteínas de Plantas/genética , RNA de Plantas/genética , Fatores de Transcrição/genética , Sequência de Bases , Marchantia/genética , MicroRNAs/metabolismo , Proteínas de Plantas/metabolismo , RNA de Plantas/metabolismo , Reprodução , Fatores de Transcrição/metabolismoRESUMO
Evolutionary mechanisms underlying innovation of cell types have remained largely unclear. In multicellular eukaryotes, the evolutionary molecular origin of sperm differentiation is unknown in most lineages. Here, we report that in algal ancestors of land plants, changes in the DNA-binding domain of the ancestor of the MYB transcription factor DUO1 enabled the recognition of a new cis-regulatory element. This event led to the differentiation of motile sperm. After neo-functionalization, DUO1 acquired sperm lineage-specific expression in the common ancestor of land plants. Subsequently the downstream network of DUO1 was rewired leading to sperm with distinct morphologies. Conjugating green algae, a sister group of land plants, accumulated mutations in the DNA-binding domain of DUO1 and lost sperm differentiation. Our findings suggest that the emergence of DUO1 was the defining event in the evolution of sperm differentiation and the varied modes of sexual reproduction in the land plant lineage.