RESUMO
Pentatricopeptide repeat (PPR) proteins constitute the largest family of proteins in angiosperms, and most members are predicted to play roles in the maturation of organellar RNAs. Here we describe the novel mitochondrial editing factor 31 (MEF31), an E-PPR protein involved in editing at two close sites in the same transcript encoding subunit C of the twin-arginine translocation (tat) pathway. MEF31 is essential for editing at site tatC-581 and application of the recently proposed amino acid code for RNA recognition by PPR proteins supports the view that MEF31 directly targets this site by recognizing its cis sequence. In contrast, editing at site tatC-586 five nucleotides downstream is only partially affected in plants lacking MEF31, being restored to wild-type levels in complemented plants. Application of the amino acid code and analysis of individual RNA molecules for editing at sites 581 and 586 suggest that MEF31 does not directly target site tatC-586, and only indirectly influences editing at this site. It is likely that editing at site tatC-581 improves recognition of the site tatC-586 cis sequence by a second unknown PPR protein.
Assuntos
Proteínas de Arabidopsis/genética , Proteínas de Cloroplastos/genética , Mitocôndrias/metabolismo , Proteínas Mitocondriais/genética , Edição de RNA/genética , Proteínas de Ligação a RNA/genética , Sequência de Aminoácidos , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/metabolismo , Sequência de Bases , Proteínas de Cloroplastos/química , Proteínas de Cloroplastos/metabolismo , Sequência Conservada/genética , Proteínas de Fluorescência Verde/metabolismo , Proteínas Mitocondriais/química , Proteínas Mitocondriais/metabolismo , Modelos Biológicos , Mutação , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas de Ligação a RNA/química , Proteínas de Ligação a RNA/metabolismo , Plântula/genéticaRESUMO
The limited development of photoprotective mechanisms, specifically heat dissipation capacity, found in micropropagated plants may be the result of low xanthophyll cycle pigment content and reduced de-epoxidation capacity making them highly susceptible to photodamage. The effects of gradual or sudden increase of light on Castanea sativa in vitro cultured and during their ex vitro transference was evaluated. The results were compared with those determined in nursery-grown plants. In vitro plants responded poorly to gradual increase in irradiance, exhibiting a low electron transport rate (ETR) agreeing with low non-photochemical quenching (NPQ) and a limited de-epoxidation capacity, not synthesizing detectable amounts of zeaxanthin (Z). Regarding a sudden increase in light (photoinhibition treatment, PhT); post-PhT as in vitro as well nursery plants showed a significant decrease in their maximal efficiency of PSII (F(v)/F(m)), but in vitro the decrease was very drastic (around 0.2) different from that observed in nursery (around 0.69). In vitro, NPQ was mainly determined by the slow relaxing component, NPQ(s) (80.8%), concomitant with a pronounced decrease of D1 protein post-PhT, and a lack of de-epoxidation capacity. During ex vitro transfer, PhT lead to death of some plants, specifically during root induction. The photoprotective mechanisms were activated over time in ex vitro conditions, indicating that micropropagated Castanea sativa display a potential for light acclimation, adjusting their photosynthetic apparatus to the ambient growth irradiance. Understanding the mechanisms that micropropagated plants deployed and how they face high light intensity events, will allow us to search for strategies to improve performance to possible light fluctuations that normally occur in ex vitro conditions during plant acclimation.