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Mitogen-activated protein kinase (MAPK)--mediated responses are in part regulated by the repertoire of MAPK substrates, which is still poorly elucidated in plants. Here, the in vivo enzyme--substrate interaction of the Arabidopsis thaliana MAP kinase, MPK6, with an ethylene response factor (ERF104) is shown by fluorescence resonance energy transfer. The interaction was rapidly lost in response to flagellin-derived flg22 peptide. This complex disruption requires not only MPK6 activity, which also affects ERF104 stability via phosphorylation, but also ethylene signaling. The latter points to a novel role of ethylene in substrate release, presumably allowing the liberated ERF104 to access target genes. Microarray data show enrichment of GCC motifs in the promoters of ERF104--up-regulated genes, many of which are stress related. ERF104 is a vital regulator of basal immunity, as altered expression in both erf104 and overexpressors led to more growth inhibition by fig22 and enhanced susceptibility to a non-adapted bacterial pathogen. defense | elicitor | FRET | signal transduction

The organization of living cells is based on networks of interacting molecules. Systematic analysis of protein interactions of 3-aa loop extension (TALE) homeodomain proteins, fundamental regulators of plant meristem function and leaf development, revealed a highly connected, complex network. The network includes nine members of Arabidopsis thaliana ovate family proteins (AtOFPs), a plant-specific protein family, indicating a close functional connection to TALE homeodomain proteins. Evidence is provided that AtOFP1 is an essential pleiotropic developmental regulator. AtOFP1 and AtOFP5 are shown to associate with the cytoskeleton and to regulate subcellular localization of TALE homeodomain proteins, suggesting a previously unrecognized control mechanism in plant development. cytoskeleton | network modules | protein-protein interactions | BELL proteins | KNOX proteins

Plant viruses have a significant impact on agronomic losses worldwide. A new strategy for engineering virus-resistant plants by transgenic expression of a dominant interfering peptide is presented here. This peptide of 29 aa strongly interacts with the nucleocapsid proteins (N) of different tospoviruses. Transgenic Nicotiana benthamiana lines expressing the peptide fused to a carrier protein were challenged with five different tospoviruses that have a nucleocapsid protein interacting with the peptide. In the transgenic plants, strong resistance to tomato spotted will virus, tomato chlorotic spot virus, groundnut ring spot virus, and chrysanthemum stem necrosis virus was observed. This therefore demonstrates the feasibility of using peptide 'aptamers' as an in vivo tool to control viral infection in higher plants.