RESUMO
Arabidopsis thaliana L. yellow variegated (var2) mutant is defective in a chloroplast FtsH family metalloprotease, AtFtsH2/VAR2, and displays an intriguing green and white leaf variegation. This unique var2-mediated leaf variegation offers a simple yet powerful tool for dissecting the genetic regulation of chloroplast development. Here, we report the isolation and characterization of a new var2 suppressor gene, SUPPRESSOR OF VARIEGATION8 (SVR8), which encodes a putative chloroplast ribosomal large subunit protein, L24. Mutations in SVR8 suppress var2 leaf variegation at ambient temperature and partially suppress the cold-induced chlorosis phenotype of var2. Loss of SVR8 causes unique chloroplast rRNA processing defects, particularly the 23S-4.5S dicistronic precursor. The recovery of the major abnormal processing site in svr8 23S-4.5S precursor indicate that it does not lie in the same position where SVR8/L24 binds on the ribosome. Surprisingly, we found that the loss of a chloroplast ribosomal small subunit protein, S21, results in aberrant chloroplast rRNA processing but not suppression of var2 variegation. These findings suggest that the disruption of specific aspects of chloroplast translation, rather than a general impairment in chloroplast translation, suppress var2 variegation and the existence of complex genetic interactions in chloroplast development.
Assuntos
Proteases Dependentes de ATP/metabolismo , Proteínas de Arabidopsis/metabolismo , Cloroplastos/genética , Proteínas de Membrana/metabolismo , Folhas de Planta/genética , Biossíntese de Proteínas/genética , Supressão Genética , Alelos , Sequência de Aminoácidos , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Sequência de Bases , Clonagem Molecular , Simulação por Computador , Genes de Plantas , Genes Supressores , Dados de Sequência Molecular , Mutação/genética , Fenótipo , Processamento Pós-Transcricional do RNA/genética , RNA Ribossômico/química , RNA Ribossômico/genética , Alinhamento de SequênciaRESUMO
High phytate content in staple food crops is a major barrier to successful iron biofortification. We have exploited the low phytic acid 1-1 (lpa1-1) mutant of maize to generate transgenic plants with up-to 70 µg/g seed iron through the endosperm-specific overexpression of soybean ferritin, resulting in more than 2-fold improvement in iron bioavailability. The levels of bioavailable seed iron achieved in this study greatly exceed any achieved thus far and closely approach values estimated to have a nutritional impact on target populations. Gene expression studies reveal a large induction of the YS1 transporter in leaves and severe repression of an iron acquisition gene DMAS1 in roots, suggesting significant alterations in the iron homeostatic mechanisms in transgenic lpa1-1. Furthermore, preliminary tests show that the high-iron lpa1-1 seeds have higher germination rates and seedling vigor when compared to those of the nontransgenic seeds, which may help improve their value to plant breeders.
Assuntos
Ferro/análise , Ferro/farmacocinética , Ácido Fítico/análise , Plantas Geneticamente Modificadas/metabolismo , Zea mays/metabolismo , Disponibilidade Biológica , Alimentos Fortificados , Plantas Geneticamente Modificadas/química , Sementes/química , Sementes/metabolismo , Zea mays/químicaRESUMO
BACKGROUND: The Arabidopsis var2 mutant displays a unique green and white/yellow leaf variegation phenotype and lacks VAR2, a chloroplast FtsH metalloprotease. We are characterizing second-site var2 genetic suppressors as means to better understand VAR2 function and to study the regulation of chloroplast biogenesis. RESULTS: In this report, we show that the suppression of var2 variegation in suppressor line TAG-11 is due to the disruption of the SUPPRESSOR OF VARIEGATION3 (SVR3) gene, encoding a putative TypA-like translation elongation factor. SVR3 is targeted to the chloroplast and svr3 single mutants have uniformly pale green leaves at 22°C. Consistent with this phenotype, most chloroplast proteins and rRNA species in svr3 have close to normal accumulation profiles, with the notable exception of the Photosystem II reaction center D1 protein, which is present at greatly reduced levels. When svr3 is challenged with chilling temperature (8°C), it develops a pronounced chlorosis that is accompanied by abnormal chloroplast rRNA processing and chloroplast protein accumulation. Double mutant analysis indicates a possible synergistic interaction between svr3 and svr7, which is defective in a chloroplast pentatricopeptide repeat (PPR) protein. CONCLUSIONS: Our findings, on one hand, reinforce the strong genetic link between VAR2 and chloroplast translation, and on the other hand, point to a critical role of SVR3, and possibly some aspects of chloroplast translation, in the response of plants to chilling stress.