RESUMO
Chlorophyll is indispensable for life on Earth. Dynamic control of chlorophyll level, determined by the relative rates of chlorophyll anabolism and catabolism, ensures optimal photosynthesis and plant fitness. How plants post-translationally coordinate these two antagonistic pathways during their lifespan remains enigmatic. Here, we show that two Arabidopsis paralogs of BALANCE of CHLOROPHYLL METABOLISM (BCM) act as functionally conserved scaffold proteins to regulate the trade-off between chlorophyll synthesis and breakdown. During early leaf development, BCM1 interacts with GENOMES UNCOUPLED 4 to stimulate Mg-chelatase activity, thus optimizing chlorophyll synthesis. Meanwhile, BCM1's interaction with Mg-dechelatase promotes degradation of the latter, thereby preventing chlorophyll degradation. At the onset of leaf senescence, BCM2 is up-regulated relative to BCM1, and plays a conserved role in attenuating chlorophyll degradation. These results support a model in which post-translational regulators promote chlorophyll homeostasis by adjusting the balance between chlorophyll biosynthesis and breakdown during leaf development.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Clorofila/biossíntese , Cisteína Endopeptidases/metabolismo , Homeostase , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/metabolismo , Biossíntese de Proteínas , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/genética , Cloroplastos/metabolismo , Cloroplastos/ultraestrutura , Sequência Conservada , Cisteína Endopeptidases/genética , Enzimas/metabolismo , Epistasia Genética , Regulação da Expressão Gênica de Plantas , Peptídeos e Proteínas de Sinalização Intracelular/genética , Modelos Biológicos , Folhas de Planta/genética , Estabilidade Proteica , Plântula/genética , Plântula/crescimento & desenvolvimentoRESUMO
Phytochrome photoreceptors mediate adaptive responses of plants to red and far-red light. These responses generally entail light-regulated association between phytochromes and other proteins, among them the phytochrome-interacting factors (PIF). The interaction with Arabidopsis thaliana phytochrome B (AtPhyB) localizes to the bipartite APB motif of the A. thaliana PIFs (AtPIF). To address a dearth of quantitative interaction data, we construct and analyze numerous AtPIF3/6 variants. Red-light-activated binding is predominantly mediated by the APB N-terminus, whereas the C-terminus modulates binding and underlies the differential affinity of AtPIF3 and AtPIF6. We identify AtPIF variants of reduced size, monomeric or homodimeric state, and with AtPhyB affinities between 10 and 700 nM. Optogenetically deployed in mammalian cells, the AtPIF variants drive light-regulated gene expression and membrane recruitment, in certain cases reducing basal activity and enhancing regulatory response. Moreover, our results provide hitherto unavailable quantitative insight into the AtPhyB:AtPIF interaction underpinning vital light-dependent responses in plants.
RESUMO
[This corrects the article DOI: 10.1038/s42003-019-0687-9.].