RESUMO
Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules present in all eukaryotes. In plants, MAPK cascades were shown to regulate cell division, developmental processes, stress responses, and hormone pathways. The subgroup A of Arabidopsis MAPKs consists of AtMPK3, AtMPK6, and AtMPK10. AtMPK3 and AtMPK6 are activated by their upstream MAP kinase kinases (MKKs) AtMKK4 and AtMKK5 in response to biotic and abiotic stress. In addition, they were identified as key regulators of stomatal development and patterning. AtMPK10 has long been considered as a pseudo-gene, derived from a gene duplication of AtMPK6. Here we show that AtMPK10 is expressed highly but very transiently in seedlings and at sites of local auxin maxima leaves. MPK10 encodes a functional kinase and interacts with the upstream MAP kinase kinase (MAPKK) AtMKK2. mpk10 mutants are delayed in flowering in long-day conditions and in continuous light. Moreover, cotyledons of mpk10 and mkk2 mutants have reduced vein complexity, which can be reversed by inhibiting polar auxin transport (PAT). Auxin does not affect AtMPK10 expression while treatment with the PAT inhibitor HFCA extends the expression in leaves and reverses the mpk10 mutant phenotype. These results suggest that the AtMKK2-AtMPK10 MAPK module regulates venation complexity by altering PAT efficiency.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Ácidos Indolacéticos/metabolismo , Quinases de Proteína Quinase Ativadas por Mitógeno/metabolismo , Folhas de Planta/anatomia & histologia , Transdução de Sinais , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Ativação Enzimática , Regulação da Expressão Gênica de Plantas , Sistema de Sinalização das MAP Quinases , Quinases de Proteína Quinase Ativadas por Mitógeno/genética , FosforilaçãoRESUMO
Mitogen-activated protein (MAP) kinases mediate cellular responses to a wide variety of stimuli. Activation of a MAP kinase occurs after phosphorylation by an upstream dual-specificity protein kinase, known as a MAP kinase kinase or MEK. The Arabidopsis thaliana genome encodes 10 MEKs but few of these have been shown directly to activate any of the 20 Arabidopsis MAP kinases. We show here that functional complementation of the cell lysis phenotype of a mutant yeast strain depends on the co-expression of the Arabidopsis MEK AtMKK6 and the MAP kinase AtMPK13. The kinase activity of AtMPK13 is stimulated in the presence of AtMKK6 in yeast cells. RT-PCR analysis showed the co-expression of these two genes in diverse plant tissues. These data show that AtMKK6 can functionally activate the MAP kinase AtMPK13.
Assuntos
Arabidopsis/enzimologia , Quinases de Proteína Quinase Ativadas por Mitógeno/metabolismo , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Arabidopsis/genética , Ativação Enzimática , Expressão Gênica , Teste de Complementação Genética , Genoma de Planta , Quinases de Proteína Quinase Ativadas por Mitógeno/genética , Proteínas Quinases Ativadas por Mitógeno/genética , Mutação , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Saccharomyces cerevisiae/genética , Transdução de Sinais , Técnicas do Sistema de Duplo-HíbridoRESUMO
Profilin is a small actin-binding protein and is expressed at high levels in mature pollen where it is thought to regulate actin filament dynamics upon pollen germination and tube growth. The majority of identified plant profilins contain a MAP kinase phosphorylation motif, P-X-T-P, and a MAP kinase interaction motif (KIM). In in vitro kinase assays, the tobacco MAP kinases p45(Ntf4) and SIPK, when activated by the tobacco MAP kinase kinase NtMEK2, can phosphorylate the tobacco profilin NtProf2. Mutagenesis of the threonine residue in this motif identified it as the site of MAP kinase phosphorylation. Fractionation of tobacco pollen extracts showed that p45(Ntf4) is found exclusively in the high-speed pellet fraction while SIPK and profilin are predominantly cytosolic. These data identify one of the first substrates to be directly phosphorylated by MAP kinases in plants.
Assuntos
Proteínas Contráteis/metabolismo , Proteínas dos Microfilamentos/metabolismo , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Nicotiana/enzimologia , Proteínas de Plantas/metabolismo , Pólen/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Proteínas Contráteis/genética , Ativação Enzimática , MAP Quinase Quinase 2/metabolismo , Proteínas dos Microfilamentos/genética , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Fosforilação , Proteínas de Plantas/genética , Pólen/química , Profilinas , Alinhamento de Sequência , Nicotiana/citologiaRESUMO
Programmed cell death (PCD) in plants is considered an integral part of development. Evidence of DNA fragmentation, occurring at specific sites and times during embryo formation in maize (Zea mays L.), was obtained using terminal deoxyribonucleotidyl transferase-mediated dUTP-fluorescein nick end labelling (TUNEL) and by genomic DNA ladder detection. During the crucial period of elaboration of the primary shoot and root axis (14-20 d after pollination), TUNEL-positive nuclei are present in the scutellum, coleoptile, root cap and principally in the suspensor. Additional evidence of a form of programmed cell death occurring in these tissues comes from the detection of a DNA ladder. Upon completion of the differentiation process, all embryonic cells are TUNEL-negative, indicating that possible programmed cell death events during maize embryogenesis are confined to structures or organs that do not contribute to the adult plant body.
