RESUMEN
Plant seeds do not contain differentiated chloroplasts. Upon germination, the seedlings thus need to gain photoautotrophy before storage energies are depleted. This requires the coordinated expression of photosynthesis genes encoded in nuclear and plastid genomes. Chloroplast biogenesis needs to be additionally coordinated with the light regulation network that controls seedling development. This coordination is achieved by nucleus to plastid signals called anterograde and plastid to nucleus signals termed retrograde. Retrograde signals sent from plastids during initial chloroplast biogenesis are also called biogenic signals. They have been recognized as highly important for proper chloroplast biogenesis and for seedling development. The molecular nature, transport, targets, and signalling function of biogenic signals are, however, under debate. Several studies disproved the involvement of a number of key components that were at the base of initial models of retrograde signalling. New models now propose major roles for a functional feedback between plastid and cytosolic protein homeostasis in signalling plastid dysfunction as well as the action of dually localized nucleo-plastidic proteins that coordinate chloroplast biogenesis with light-dependent control of seedling development. This review provides a survey of the developments in this research field, summarizes the unsolved questions, highlights several recent advances, and discusses potential new working modes.
Asunto(s)
Genoma de Plastidios , Plastidios , Cloroplastos , Proteínas de Cloroplastos , FotosíntesisRESUMEN
Chloroplast biogenesis depends on a complex transcriptional program involving coordinated expression of plastid and nuclear genes. In particular, photosynthesis-associated plastid genes are expressed by the plastid-encoded polymerase (PEP) that undergoes a structural rearrangement during chloroplast formation. The prokaryotic-type core enzyme is rebuilt into a larger complex by the addition of nuclear-encoded PEP-associated proteins (PAP1 to PAP12). Among the PAPs, some have been detected in the nucleus (PAP5 and PAP8), where they could serve a nuclear function required for efficient chloroplast biogenesis. Here, we detected PAP8 in a large nuclear subcomplex that may include other subunits of the plastid-encoded RNA polymerase. We have made use of PAP8 recombinant proteins in Arabidopsis thaliana to decouple its nucleus- and chloroplast-associated functions and found hypomorphic mutants pointing at essential amino acids. While the origin of the PAP8 gene remained elusive, we have found in its sequence a micro-homologous domain located within a large structural homology with a rhinoviral RNA-dependent RNA polymerase, highlighting potential RNA recognition motifs in PAP8. PAP8 in vitro RNA binding activity suggests that this domain is functional. Hence, we propose that the acquisition of PAPs may have occurred during evolution by different routes, including lateral gene transfer.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Cloroplastos/metabolismo , ARN Polimerasas Dirigidas por ADN/genética , ARN Polimerasas Dirigidas por ADN/metabolismo , Regulación de la Expresión Génica de las Plantas , Mutación , Proteínas Nucleares/genética , Plastidios/metabolismo , Motivo de Reconocimiento de ARNRESUMEN
The initial greening of angiosperms involves light activation of photoreceptors that trigger photomorphogenesis, followed by the development of chloroplasts. In these semi-autonomous organelles, construction of the photosynthetic apparatus depends on the coordination of nuclear and plastid gene expression. Here, we show that the expression of PAP8, an essential subunit of the plastid-encoded RNA polymerase (PEP) in Arabidopsis thaliana, is under the control of a regulatory element recognized by the photomorphogenic factor HY5. PAP8 protein is localized and active in both plastids and the nucleus, and particularly required for the formation of late photobodies. In the pap8 albino mutant, phytochrome-mediated signalling is altered, degradation of the chloroplast development repressors PIF1/PIF3 is disrupted, HY5 is not stabilized, and the expression of the photomorphogenesis regulator GLK1 is impaired. PAP8 translocates into plastids via its targeting pre-sequence, interacts with the PEP and eventually reaches the nucleus, where it can interact with another PEP subunit pTAC12/HMR/PAP5. Since PAP8 is required for the phytochrome B-mediated signalling cascade and the reshaping of the PEP activity, it may coordinate nuclear gene expression with PEP-driven chloroplastic gene expression during chloroplast biogenesis.
Asunto(s)
Fosfatasa Ácida/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Cloroplastos/metabolismo , Morfogénesis/fisiología , Plastidios/genética , Plastidios/metabolismo , Fosfatasa Ácida/genética , Proteínas de Arabidopsis/genética , Núcleo Celular/metabolismo , Cloroplastos/genética , ARN Polimerasas Dirigidas por ADN/metabolismo , Regulación de la Expresión Génica de las Plantas , Luz , Biogénesis de Organelos , Fitocromo/metabolismo , Plantas Modificadas Genéticamente , Transducción de Señal , Factores de Transcripción , Transcripción GenéticaRESUMEN
The expectations and role of families in the care of children with autism spectrum disorder are increasingly important. Nonetheless, no study has thus far explored the perspectives of siblings about the care received by a brother or sister with this disorder. The objective of this study was to fill this gap in the literature. This multicentre qualitative study took place in France, where we conducted semi-structured interviews with adolescents who were older siblings of children receiving care in a day hospital for an autism spectrum disorder. Data collection by purposive sampling continued until we reached 'theoretical sufficiency', and data analysis was thematic. The study included 20 participants: 13 sisters and 7 brothers. Four themes emerged in the data analysis: (1) the treatment targets, (2) the treatment's perceived effectiveness, (3) the complex questions it raises and (4) the role of intrafamily relationships. Our results allowed us to report original aspects of the experience of siblings, in particular, their confusion with regard to the treatment, their difficulty in separating themselves from their parents' discourse and their assertion of their role as caregivers for their younger brothers and sisters.