RESUMO
The Arabidopsis thaliana floral homeotic gene AGAMOUS (AG) plays a central role in reproductive organ (stamen and carpel) development. AG RNA is expressed in the center of floral primordia from a time prior to the initiation of stamen and carpel primordia until late in flower development. While early AG expression acts in specification of stamens and carpels, the role, if any, of continued AG expression in later flower development is unknown. To examine the timing of AG action and its possible late-stage functions, we performed a series of time-course experiments using a transgenic line with inducible AG activity in an ag homozygous mutant background. We show that AG controls late-stage stamen development, including anther morphogenesis and dehiscence, as well as filament formation and elongation. We further show that AG coordinates late stamen maturation by controlling a biosynthetic gene of the lipid-derived phytohormone jasmonic acid (JA). Expression analysis and in vivo binding of AG indicate that AG directly regulates the transcription of a catalytic enzyme of JA, DEFECTIVE IN ANTHER DEHISCENCE1. Our results indicate that stamen identity and differentiation control by AG is achieved by the regulation of different transcriptional cascades in different floral stages, with organ specification induced early, followed by phytohormone biosynthesis to coordinate stamen maturation.
Assuntos
Proteína AGAMOUS de Arabidopsis/metabolismo , Arabidopsis/embriologia , Arabidopsis/genética , Ciclopentanos/metabolismo , Flores/embriologia , Flores/genética , Regulação da Expressão Gênica de Plantas , Oxilipinas/metabolismo , Acetatos/farmacologia , Arabidopsis/efeitos dos fármacos , Arabidopsis/enzimologia , Proteínas de Arabidopsis/genética , Catálise/efeitos dos fármacos , Núcleo Celular/efeitos dos fármacos , Núcleo Celular/metabolismo , Ciclopentanos/farmacologia , Dexametasona/farmacologia , Flores/enzimologia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes de Plantas , Ácido Linoleico/farmacologia , Oxilipinas/farmacologia , Fosfolipases A/genética , Fosfolipases A1/genética , Regiões Promotoras Genéticas/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Fatores de TempoRESUMO
Polyamines (PAs) are low molecular weight metabolites involved in various physiological and developmental processes in eukaryotic and prokaryotic cells. The cellular PA level is regulated in part by the action of amine oxidases (AOs) including copper diamine oxidases (DAOs) and flavoprotein polyamine oxidases (PAOs). In this study, the isolation and characterization of flavin amine oxidases (FAOs) from Brassica juncea (BJFAO) and Arabidopsis (ATFAO1) are reported that were clustered in the same group as polyamine oxidases from maize (MPAO) and barley (BPAO1) and monoamine oxidases from mammalian species. ATFAO1 was temporally and spatially regulated in Arabidopsis and showed distinct expression patterns in response to different stress treatments. To investigate the in vivo function of FAO, transgenic Arabidopsis plants expressing sense, antisense, and double-stranded BJFAO RNAs were generated and those with altered activity of FAOs were selected for further characterization. It was found that the shoot regeneration response in transgenic plants was significantly affected by the modulated PA levels corresponding to FAO activities. Tissues that originated from transgenic plants with down-regulated FAO activity were highly regenerative, while those from transgenic plants with upregulated FAO activity were poorly regenerative. The shoot regeneration capacity in these transgenic plants was related to the levels of individual PAs, suggesting that FAO affects shoot regeneration by regulating cellular PAs. Furthermore, it was found that the effect of FAO activity on shoot regeneration was exerted downstream of the Enhancer of Shoot Regeneration (ESR1) gene, which may function in a branch of the cytokinin signalling pathway.
