RESUMO
The tomato Mi gene confers resistance against root-knot nematodes and potato aphids. Chimeric constructs of the functional gene, Mi-1. 2, with a homolog, Mi-1.1, were produced, and their phenotypes were examined in Agrobacterium rhizogenes-transformed roots. Exchange of the leucine-rich repeat (LRR) region of Mi-1.1 into Mi-1.2 resulted in the loss of ability to confer nematode resistance, as did substitution of a 6-amino acid sequence from the Mi-1.1 LRR into Mi-1.2. Introduction of the Mi-1.2 LRR-encoding region into Mi-1.1 resulted in a lethal phenotype, as did substitution of the fragment encoding the N-terminal 161 amino acids of Mi-1.1 into Mi-1.2. Transient expression of the latter two chimeric constructs in Nicotiana benthamiana leaves produced localized cell death. The cell death caused by the N-terminal exchange was suppressed by coinfiltration with a construct expressing the N-terminal 161 amino acids of Mi-1.2. The phenotypes of these and other constructs indicate that the LRR region of Mi-1.2 has a role in signaling localized cell death and that the N-terminal 161 amino acids have a role in regulating this death.
Assuntos
Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/metabolismo , Leucina/metabolismo , Sequências Repetitivas de Aminoácidos , Solanum lycopersicum/citologia , Solanum lycopersicum/parasitologia , Fatores de Transcrição , Sequência de Aminoácidos , Animais , Afídeos/fisiologia , Morte Celular , Proteínas de Ligação a DNA/genética , Genes Letais/genética , Genes de Plantas/genética , Predisposição Genética para Doença , Interações Hospedeiro-Parasita , Leucina/genética , Solanum lycopersicum/genética , Fator de Transcrição Associado à Microftalmia , Modelos Biológicos , Dados de Sequência Molecular , Doenças das Plantas/genética , Doenças das Plantas/parasitologia , Folhas de Planta/citologia , Folhas de Planta/genética , Folhas de Planta/parasitologia , Raízes de Plantas/citologia , Raízes de Plantas/genética , Raízes de Plantas/parasitologia , Plantas Geneticamente Modificadas , Plantas Tóxicas , RNA Mensageiro/análise , RNA Mensageiro/genética , RNA de Plantas/análise , RNA de Plantas/genética , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Rhizobium/genética , Alinhamento de Sequência , Transdução de Sinais , Nicotiana/citologia , Nicotiana/genética , Nicotiana/parasitologia , Tylenchoidea/fisiologiaRESUMO
Ras is a low-molecular-weight guanine nucleotide (GDP/GTP)-binding protein that transduces signals for growth and differentiation in eukaryotes. In mammals, the importance of Ras in regulating growth is underscored by the observation that activating mutations in ras genes are found in many animal tumors. Colletorichum trifolii is a filamentous fungal pathogen of alfalfa which causes anthracnose disease. To investigate signaling pathways that regulate growth and development in this fungus, a gene encoding a Ras homolog (CT-Ras) was cloned from C. trifolii. CT-Ras exhibited extensive amino acid similarity to Ras proteins from higher and lower eukaryotes. A single amino acid change resulting in mutationally activated CT-Ras induced cellular transformation of mouse (NIH 3T3) fibroblasts and tumor formation in nu/nu mice. In Colletotrichum, mutationally activated CT-Ras induced abnormal hyphal proliferation and defects in polarized growth, and significantly reduced differentiation in a nutrient-dependent manner. These results show that C. trifolii Ras is a functional growth regulator in both mammals and fungi, and demonstrate that proper regulation of Ras is required for normal fungal growth and development.
Assuntos
Polaridade Celular/genética , Transformação Celular Neoplásica/genética , Colletotrichum/genética , Genes Fúngicos , Proteínas ras/genética , Células 3T3 , Sequência de Aminoácidos , Animais , Colletotrichum/citologia , Proteínas Fúngicas/genética , Camundongos , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Mutação , Análise de Sequência de DNA , Homologia de Sequência de Aminoácidos , Transformação GenéticaRESUMO
Differential display of mRNA was used to isolate a full-length (SRG1) and a partial (SRG2) alfalfa cDNA induced during infection with the fungal pathogen Colletotrichum trifolii. The deduced amino acid sequences are similar to each other and resemble plant defense-related proteins and tree pollen allergens. SRG1 is a member of a gene family in alfalfa, which may also include the putative defense-related gene PR10. Unlike many defense-related genes described in similar systems, expression of SRG1-like genes does not correlate with resistance to C. trifolii. We speculate SRG1 is induced in response to plant stress.
Assuntos
Proteínas de Choque Térmico/genética , Medicago sativa/genética , Fungos Mitospóricos/patogenicidade , Doenças das Plantas/genética , Proteínas de Plantas/genética , Sequência de Aminoácidos , Sequência de Bases , DNA Complementar/genética , Expressão Gênica , Dados de Sequência Molecular , RNA Mensageiro/genética , RNA de Plantas/genética , Homologia de Sequência de AminoácidosRESUMO
Colletotrichum trifolii is a fungal pathogen which is responsible for anthracnose disease of alfalfa. To initiate research on molecular communication in this fungus, a kinase-encoding gene (TB3) and the corresponding cDNA were cloned and sequenced. The deduced amino acid sequence of TB3 closely resembles that of a Neurospora crassa serine/threonine protein kinase, COT1, required for hyphal elongation and branching. The C-terminal catalytic domains of TB3 and COT1 are highly conserved but the N-terminal regions are divergent, particularly in the homopolymeric glutamine repeats of TB3. Northern analysis indicated that TB3 expression was highest 1 h after inducing conidial germination and 1 h before germ tubes were first observed. Expression of TB3 transcripts returned to constitutive levels by 4 h after induction of germination. TB3 complemented the cot-I mutant of Neurospora crassa, demonstrating the functional conservation of this kinase between a pathogenic and a saprophytic fungus.
