RESUMEN
The regulation of plant gene expression, necessary for development and adaptive responses, relies not only on RNA transcription but also on messenger RNA (mRNA) fate. To understand whether seed germination relies on the degradation of specific subsets of mRNA, we investigated whether the 5' to 3' RNA decay machinery participated in the regulation of this process. Arabidopsis (Arabidopsis thaliana) seeds of exoribonuclease4 (xrn4) and varicose (vcs) mutants displayed distinct dormancy phenotypes. Transcriptome analysis of xrn4-5 and vcs-8 mutant seeds allowed us to identify genes that are likely to play a role in the control of germination. Study of 5' untranslated region features of these transcripts revealed that specific motifs, secondary energy, and GC content could play a role in their degradation by XRN4 and VCS, and Gene Ontology clustering revealed novel actors of seed dormancy and germination. Several specific transcripts identified as being putative targets of XRN4 and VCS in seeds (PECTIN LYASE-LIKE, ASPARTYL PROTEASE, DWD-HYPERSENSITIVE-TO-ABA3, and YELLOW STRIPE-LIKE5) were further studied by reverse genetics, and their functional roles in the germination process were confirmed by mutant analysis. These findings suggest that completion of germination and its regulation by dormancy also depend on the degradation of specific subsets of mRNA.
Asunto(s)
Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas , Germinación/genética , Latencia en las Plantas/genética , ARN Mensajero/genética , Semillas/genética , Regiones no Traducidas 5'/genética , Ácido Abscísico/metabolismo , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Composición de Base/genética , Secuencia de Bases , Análisis por Conglomerados , Exorribonucleasas/genética , Exorribonucleasas/metabolismo , Perfilación de la Expresión Génica/métodos , Ontología de Genes , Mutación , Motivos de Nucleótidos/genética , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Estabilidad del ARN/genética , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Semillas/crecimiento & desarrolloRESUMEN
Dormancy is a complex evolutionary trait that temporally prevents seed germination, thus allowing seedling growth at a favorable season. High-throughput analyses of transcriptomes have led to significant progress in understanding the molecular regulation of this process, but the role of posttranscriptional mechanisms has received little attention. In this work, we have studied the dynamics of messenger RNA association with polysomes and compared the transcriptome with the translatome in dormant and nondormant seeds of Arabidopsis (Arabidopsis thaliana) during their imbibition at 25 °C in darkness, a temperature preventing germination of dormant seeds only. DNA microarray analysis revealed that 4,670 and 7,028 transcripts were differentially abundant in dormant and nondormant seeds in the transcriptome and the translatome, respectively. We show that there is no correlation between transcriptome and translatome and that germination regulation is also largely translational, implying a selective and dynamic recruitment of messenger RNAs to polysomes in both dormant and nondormant seeds. The study of 5' untranslated region features revealed that GC content and the number of upstream open reading frames could play a role in selective translation occurring during germination. Gene Ontology clustering showed that the functions of polysome-associated transcripts differed between dormant and nondormant seeds and revealed actors in seed dormancy and germination. In conclusion, our results demonstrate the essential role of selective polysome loading in this biological process.
Asunto(s)
Arabidopsis/embriología , Arabidopsis/genética , Germinación/genética , Polirribosomas/metabolismo , ARN Mensajero/metabolismo , Semillas/embriología , Regiones no Traducidas 5'/genética , Secuencia de Bases , Regulación de la Expresión Génica de las Plantas , Ontología de Genes , Modelos Biológicos , Datos de Secuencia Molecular , Sistemas de Lectura Abierta/genética , Latencia en las Plantas/genética , Biosíntesis de Proteínas/genética , ARN Mensajero/genética , Semillas/genética , Transcriptoma/genéticaRESUMEN
The changes in germination potential of freshly harvested seeds of Arabidopsis thaliana stored in various combinations of temperature and relative humidity were investigated over 63 weeks of storage. Seeds of the wild type Col-0 and of two mutants displaying low and high levels of dormancy, cat2-1 and mtr4-1, respectively, were stored at harvest in 24 different environments including a combination of eight relative humidities, from 1 to 85%, and four temperatures (10, 15, 20, and 25 °C). These mutations did not influence behaviour of seeds during storage. Primary dormant seeds did not germinate in darkness at 25 °C but acquired the potential to germinate at this temperature within 7 weeks when stored in relative humidities close to 50% across all temperatures. Sorption isotherms and Arrhenius plots demonstrated that the seed moisture content of 0.06 g H2O/g dry weight was a critical value below which dormancy release was associated with reactions of negative activation energy and above which dormancy release increased with temperature. Longer storage times when relative humidity did not exceed 75-85% led to decreased germination at 25 °C, corresponding to the induction of secondary dormancy. Dormancy release and induction of secondary dormancy in the dry state were associated with induction or repression of key genes related to abscisic acid and gibberellins biosynthesis and signalling pathways. In high relative humidity, prolonged storage of seeds induced ageing and progressive loss of viability, but this was not related to the initial level of dormancy.