Plastid Signals Remodel Light Signaling Networks and Are Essential for Efficient Chloroplast Biogenesis inArabidopsis

Abstract

Plastid signals are among the most potent regulators of genes that encode proteins active in photosynthesis. Plastid signals help coordinate the expression of the nuclear and chloroplast genomes and the expression of genes with the functional state of the chloroplast. Here, we report the isolation of new cryptochrome1 (cry1) alleles from a screen for Arabidopsis thaliana genomes uncoupled mutants, which have defects in plastid-to-nucleus signaling. We also report genetic experiments showing that a previously unidentified plastid signal converts multiple light signaling pathways that perceive distinct qualities of light from positive to negative regulators of some but not all photosynthesis-associated nuclear genes (PhANGs) and change the fluence rate response of PhANGs. At least part of this remodeling of light signaling networks involves converting HY5, a positive regulator of PhANGs, into a negative regulator of PhANGs. We also observed that mutants with defects in both plastid-to-nucleus and cry1 signaling exhibited severe chlorophyll deficiencies. These data show that the remodeling of light signaling networks by plastid signals is a mechanism that plants use to integrate signals describing the functional and developmental state of plastids with signals describing particular light environments when regulating PhANG expression and performing chloroplast biogenesis.

Influence of plastids on light signalling and development

“…These data indicate that gun mutant screens specifically disrupted a few distinct mechanisms that downregulate the expression of PhANGs when chloroplast biogenesis is blocked, not complex metabolic situations. The findings that these mechanisms appear conserved in all plants tested [17] and contribute to stress tolerance [4,5,11,14], the circadian rhythm [7,8] and development [38][39][40][41] provide evidence that they contribute plastid-to-nucleus signalling in natural environments.…”

“…Norflurazon specifically inhibits phytoene desaturase, which is required for carotenoid biosynthesis and chloroplast biogenesis [17]. gun alleles either attenuate negative regulators or promote positive regulators of PhANG expression [5,18,[20][21][22][23][24][25].…”

“…gun mutant screens use reporter genes to screen for Arabidopsis mutants that transcribe elevated levels of PhANGs when chloroplast biogenesis is blocked with norflurazon treatments [5,18,[20][21][22]. Norflurazon specifically inhibits phytoene desaturase, which is required for carotenoid biosynthesis and chloroplast biogenesis [17].…”

“…Extraplastidic signalling mechanisms, plastid-to-nucleus signalling mechanisms and the integration of these signalling mechanisms are major regulators of photosynthesis-associated nuclear genes (PhANGs) [1][2][3]. Plastidto-nucleus signalling affects numerous plastidic and extraplastidic processes, such as the biogenesis of chloroplasts and amyloplasts [3][4][5][6], the circadian rhythm [7,8], DNA replication [3], the transcription of genes that encode ribosomal RNA by RNA polymerase I [9], development [10] and the optimization of photosynthesis to various qualities of light [3]. Plastid-to-nucleus signalling also contributes to the response to wounding, biotic stress, abiotic stress and sugar [2,3,9,[11][12][13][14].…”

Teores de pigmentos fotossintéticos e estrutura de cloroplastos de Alfavaca-cravo cultivadas sob malhas coloridas

“…Esses resultados expressam que a biogênese dos cloroplastos em alfavaca-cravo pode ser controlada por alterações na intensidade e na qualidade espectral da radiação no ambiente de cultivo. JIAO et al (2007) e RUCKLE et al (2007 demonstraram que a rota de transdução de sinal para a biossíntese de cloroplasto envolve criptocromos sensíveis às variações no conteúdo de luz azul da radiação total.…”