RESUMO
Screening of a yeast two-hybrid library for proteins that interact with the kinase domain of an S-locus receptor kinase (SRK) resulted in the isolation of a plant protein called ARC1 (Arm Repeat Containing). This interaction was mediated by the C-terminal region of ARC1 in which five arm repeat units were identified. Using the yeast two-hybrid system and in vitro binding assays, ARC1 was found to interact specifically with the kinase domains from SRK-910 and SRK-A14 but failed to interact with kinase domains from two different Arabidopsis receptor-like kinases. In addition, treatment with a protein phosphatase or the use of a kinase-inactive mutant reduced or abolished the binding of ARC1 to the SRK-910 kinase domain, indicating that the interaction was phosphorylation dependent. Lastly, RNA blot analysis revealed that the expression of ARC1 is restricted to the stigma, the site of the self-incompatibility response.
Assuntos
Glicoproteínas/metabolismo , Proteínas de Plantas/metabolismo , Proteínas Quinases/metabolismo , Proteínas de Saccharomyces cerevisiae , Sequência de Aminoácidos , Arabidopsis/enzimologia , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Dados de Sequência Molecular , Fosforilação , RNA Ribossômico 18S/metabolismo , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismoRESUMO
To determine potential targets of the S locus receptor kinase (SRK) during the Brassica self-incompatibility response, a yeast two-hybrid library was screened with the SRK-910 protein kinase domain. Two thioredoxin-h-like clones, THL-1 and THL-2, were found to interact specifically with the SRK-910 protein kinase domain and not to interact with the protein kinase domains from the Arabidopsis receptor-like protein kinases (RLK) RLK4 and RLK5. The interaction between THL-1 and the SRK-910 protein kinase domain was confirmed using coimmunoprecipitation experiments with fusion proteins produced in Escherichia coli. THL-1 has thioredoxin activity based on an insulin reduction assay, and THL-1 is weakly phosphorylated by the SRK-910 protein kinase domain. THL-1 and THL-2 are both expressed in a variety of tissues but show some differences in steady state mRNA levels, with THL-2 being preferentially expressed in floral tissues. This indicates a more general biological function for these thioredoxins in addition to a potential role as effector molecules in the self-incompatibility signal cascade.