RESUMO
A variety of plants in diverse taxa can reproduce asexually via vegetative propagation, in which clonal propagules with a new meristem(s) are generated directly from vegetative organs. A basal land plant, Marchantia polymorpha, develops clonal propagules, gemmae, on the gametophyte thallus from the basal epidermis of a specialized receptacle, the gemma cup. Here we report an R2R3-MYB transcription factor, designated GEMMA CUP-ASSOCIATED MYB1 (GCAM1), which is an essential regulator of gemma cup development in M. polymorpha. Targeted disruption of GCAM1 conferred a complete loss of gemma cup formation and gemma generation. Ectopic overexpression of GCAM1 resulted in formation of cell clumps, suggesting a function of GCAM1 in suppression of cell differentiation. Although gemma cups are a characteristic gametophyte organ for vegetative reproduction in a taxonomically restricted group of liverwort species, phylogenetic and interspecific complementation analyses support the orthologous relationship of GCAM1 to regulatory factors of axillary meristem formation, e.g., Arabidopsis REGULATOR OF AXILLARY MERISTEMS and tomato Blind, in angiosperm sporophytes. The present findings in M. polymorpha suggest an ancient acquisition of a transcriptional regulator for production of asexual propagules in the gametophyte and the use of the regulatory factor for diverse developmental programs, including axillary meristem formation, during land plant evolution.
Assuntos
Marchantia/fisiologia , Proteínas de Plantas/genética , Reprodução Assexuada , Fatores de Transcrição/genética , Perfilação da Expressão Gênica , Marchantia/genética , Meristema/metabolismo , Proteínas de Plantas/metabolismo , Fatores de Transcrição/metabolismo , Regulação para CimaRESUMO
The diffusion efficiency of oxygen in the atmosphere, like that of CO2, is approximately 104 times greater than that in aqueous environments. Consequently, terrestrial photosynthetic organisms need mechanisms to protect against potential oxidative damage. The liverwort Marchantia polymorpha, a basal land plant, has habitats where it is exposed to both water and the atmosphere. Furthermore, like cyanobacteria, M. polymorpha has genes encoding flavodiiron proteins (FLV). In cyanobacteria, FLVs mediate oxygen-dependent alternative electron flow (AEF) to suppress the production of reactive oxygen species. Here, we investigated whether FLVs are required for the protection of photosynthesis in M. polymorpha A mutant deficient in the FLV1 isozyme (ΔMpFlv1) sustained photooxidative damage to photosystem I (PSI) following repetitive short-saturation pulses of light. Compared with the wild type (Takaragaike-1), ΔMpFlv1 showed the same photosynthetic oxygen evolution rate but a lower electron transport rate during the induction phase of photosynthesis. Additionally, the reaction center chlorophyll in PSI, P700, was highly reduced in ΔMpFlv1 but not in Takaragaike-1. These results indicate that the gene product of MpFlv1 drives AEF to oxidize PSI, as in cyanobacteria. Furthermore, FLV-mediated AEF supports the production of a proton motive force to possibly induce the nonphotochemical quenching of chlorophyll fluorescence and suppress electron transport in the cytochrome b6/f complex. After submerging the thalli, a decrease in photosystem II operating efficiency was observed, particularly in ΔMpFlv1, which implies that species living in these sorts of habitats require FLV-mediated AEF.
Assuntos
Flavoproteínas/metabolismo , Marchantia/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Proteínas de Plantas/metabolismo , Clorofila/metabolismo , Complexo Citocromos b6f/genética , Complexo Citocromos b6f/metabolismo , Transporte de Elétrons/genética , Flavoproteínas/genética , Regulação da Expressão Gênica de Plantas , Luz , Marchantia/genética , Mutação , Oxigênio/metabolismo , Fotossíntese/genética , Fotossíntese/efeitos da radiação , Complexo de Proteína do Fotossistema I/genética , Complexo de Proteína do Fotossistema II/genética , Complexo de Proteína do Fotossistema II/metabolismo , Proteínas de Plantas/genética , Força Próton-Motriz/efeitos da radiação , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fatores de TempoRESUMO
The plant hormone auxin (indole-3-acetic acid [IAA]) has previously been suggested to regulate diverse forms of dormancy in both seed plants and liverworts. Here, we use loss- and gain-of-function alleles for auxin synthesis- and signaling-related genes, as well as pharmacological approaches, to study how auxin regulates development and dormancy in the gametophyte generation of the liverwort Marchantia polymorpha. We found that M. polymorpha possess the smallest known toolkit for the indole-3-pyruvic acid (IPyA) pathway in any land plant and that this auxin synthesis pathway mainly is active in meristematic regions of the thallus. Previously a Trp-independent auxin synthesis pathway has been suggested to produce a majority of IAA in bryophytes. Our results indicate that the Trp-dependent IPyA pathway produces IAA that is essential for proper development of the gametophyte thallus of M. polymorpha. Furthermore, we show that dormancy of gemmae is positively regulated by auxin synthesized by the IPyA pathway in the apex of the thallus. Our results indicate that auxin synthesis, transport, and signaling, in addition to its role in growth and development, have a critical role in regulation of gemmae dormancy in M. polymorpha.
