RESUMO
The timing of seed germination is controlled by the combination of internal dormancy and external factors. Temperature is a major environmental factor for seed germination. The permissive temperature range for germination is narrow in dormant seeds and expands during after-ripening (AR) (dormancy release). Quantitative trait loci analyses of preharvest sprouting in cereals have revealed that MKK3, a mitogen-activated protein kinase (MAPK) cascade protein, is a negative regulator of grain dormancy. Here, we show that the MAPKKK19/20-MKK3-MPK1/2/7/14 cascade modulates the germination temperature range in Arabidopsis seeds by elevating the germinability of the seeds at sub- and supraoptimal temperatures. The expression of MAPKKK19 and MAPKKK20 is induced around optimal temperature for germination in after-ripened seeds but repressed in dormant seeds. MPK7 activation depends on the expression levels of MAPKKK19/20, with expression occurring under conditions permissive for germination. Abscisic acid (ABA) and gibberellin (GA) are two major phytohormones which are involved in germination control. Activation of the MKK3 cascade represses ABA biosynthesis enzyme gene expression and induces expression of ABA catabolic enzyme and GA biosynthesis enzyme genes, resulting in expansion of the germinable temperature range. Our data demonstrate that the MKK3 cascade integrates temperature and AR signals to phytohormone metabolism and seed germination.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Regulação da Expressão Gênica de Plantas , Germinação , Sementes , Temperatura , Germinação/fisiologia , Germinação/genética , Arabidopsis/genética , Arabidopsis/metabolismo , Arabidopsis/crescimento & desenvolvimento , Sementes/crescimento & desenvolvimento , Sementes/metabolismo , Sementes/genética , Proteínas de Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , MAP Quinase Quinase 3/metabolismo , MAP Quinase Quinase 3/genética , Sistema de Sinalização das MAP Quinases/fisiologia , Dormência de Plantas/genética , Dormência de Plantas/fisiologia , Transdução de Sinais , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Proteínas Quinases Ativadas por Mitógeno/genéticaRESUMO
Abscisic acid (ABA) is a phytohormone that promotes leaf senescence in response to environmental stress. We previously identified methyl CpG-binding domain 10 (MBD10) as a phosphoprotein that becomes differentially phosphorylated after ABA treatment in Arabidopsis. ABA-induced leaf senescence was delayed in mbd10 knockout plants but accelerated in MBD10-overexpressing plants, suggesting that MBD10 positively regulates ABA-induced leaf senescence. ABA-induced phosphorylation of MBD10 occurs in planta on Thr-89, and our results demonstrated that Thr-89 phosphorylation is essential for MBD10's function in leaf senescence. The in vivo phosphorylation of Thr-89 in MBD10 was significantly downregulated in a quadruple mutant of group C MAPKs (mpk1/2/7/14), and group C MAPKs directly phosphorylated MBD10 in vitro. Furthermore, mpk1/2/7/14 showed a similar phenotype as seen in mbd10 for ABA-induced leaf senescence, suggesting that group C MAPKs are the cognate kinases of MBD10 for Thr-89. Because group C MAPKs have been reported to function downstream of SnRK2s, our results indicate that group C MAPKs and MBD10 constitute a regulatory pathway for ABA-induced leaf senescence.
Assuntos
Ácido Abscísico , Proteínas de Arabidopsis , Arabidopsis , Proteínas Quinases Ativadas por Mitógeno , Folhas de Planta , Senescência Vegetal , Ácido Abscísico/metabolismo , Ácido Abscísico/farmacologia , Arabidopsis/genética , Arabidopsis/fisiologia , Proteínas de Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Folhas de Planta/genética , Folhas de Planta/fisiologia , Folhas de Planta/metabolismo , Fosforilação , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Proteínas Quinases Ativadas por Mitógeno/genética , Senescência Vegetal/genética , Reguladores de Crescimento de Plantas/metabolismo , Regulação da Expressão Gênica de Plantas , Plantas Geneticamente ModificadasRESUMO
Seed dormancy is an adaptive trait that enables plants to survive adverse conditions and restart growth in a season and location suitable for vegetative and reproductive growth. Control of seed dormancy is also important for crop production and food quality because it can help induce uniform germination and prevent preharvest sprouting. Rice preharvest sprouting quantitative trait locus analysis has identified Seed dormancy 4 (Sdr4) as a positive regulator of dormancy development. Here, we analyzed the loss-of-function mutant of the Arabidopsis ortholog, Sdr4 Like1 (SFL1), and found that the sfl1-1 seeds showed precocious germination at the mid- to late-maturation stage similar to rice sdr4 mutant, but converted to become more dormant than the wild type during maturation drying. Coordinated with the dormancy levels, expression levels of the seed maturation and dormancy master regulator genes, ABI3, FUS3, and DOG1 in sfl1-1 seeds were lower than in wild type at early- and mid-maturation stages, but higher at the late-maturation stage. In addition to the seed dormancy phenotype, sfl1-1 seedlings showed a growth arrest phenotype and heterochronic expression of LAFL (LEC1, ABI3, FUS3, LEC2) and DOG1 in the seedlings. These data suggest that SFL1 is a positive regulator of initiation and termination of the seed dormancy program. We also found genetic interaction between SFL1 and the SFL2, SFL3, and SFL4 paralogs of SFL1, which impacts on the timing of the phase transition from embryo maturation to seedling growth.
