RESUMO
Light-dependent seed germination is a vital process for many seed plants. A decisive event in light-induced germination is degradation of the central repressor PHYTOCHROME INTERACTING FACTOR 1 (PIF1). The balance between gibberellic acid (GA) and abscisic acid (ABA) helps to control germination. However, the cellular mechanisms linking PIF1 turnover to hormonal balancing remain elusive. Here, employing far-red light-induced Arabidopsis thaliana seed germination as the experimental system, we identified PLANTACYANIN (PCY) as an inhibitor of germination. It is a blue copper protein associated with the vacuole that is both highly expressed in mature seeds and rapidly silenced during germination. Molecular analyses showed that PIF1 binds to the miR408 promoter and represses miR408 accumulation. This in turn posttranscriptionally modulates PCY abundance, forming the PIF1-miR408-PCY repression cascade for translating PIF1 turnover to PCY turnover during early germination. Genetic analysis, RNA-sequencing, and hormone quantification revealed that PCY is necessary and sufficient to maintain the PIF1-mediated seed transcriptome and the low-GA-high-ABA state. Furthermore, we found that PCY domain organization and regulation by miR408 are conserved features in seed plants. These results revealed a cellular mechanism whereby PIF1-relayed external light signals are converted through PCY turnover to internal hormonal profiles for controlling seed germination.
Assuntos
Proteínas de Arabidopsis/metabolismo , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Germinação , Luz , Metaloproteínas/metabolismo , MicroRNAs/metabolismo , Sementes/crescimento & desenvolvimento , Transdução de Sinais , Ácido Abscísico/metabolismo , Proteínas de Arabidopsis/genética , Sequência de Bases , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Sequência Conservada , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Inativação Gênica , Genes de Plantas , Germinação/genética , Giberelinas/metabolismo , MicroRNAs/genética , Modelos Biológicos , Filogenia , Regiões Promotoras Genéticas/genética , Ligação Proteica/genética , Ligação Proteica/efeitos da radiação , Plântula/efeitos da radiação , Sementes/genética , Transdução de Sinais/efeitos da radiação , Vacúolos/metabolismo , Vacúolos/efeitos da radiaçãoRESUMO
The Casparian strip (CS) is a tight junction-like structure formed by lignin impregnation on the walls of endodermal cells in plant roots. The CS membrane domain (CSDM), demarked by the CASP proteins, is important for orienting lignification enzymes. Here, we report that an endodermis-expressed multicopper oxidase, LACCASE3 (LAC3) in Arabidopsis, locates to the interface between lignin domains and the cell wall during early CS development prior to CASP1 localizing to CSDM and eventually flanks the mature CS. Pharmacological perturbation of LAC3 causes dispersed localization of CASP1 and compensatory ectopic lignification. These results support the existence of a LAC3-based CS wall domain which coordinates with CSDM to provide bidirectional positional information that guides precise CS lignification.
