Transcription in plastids is mediated by a plastid-encoded multimeric (PEP) and a nuclear-encoded single-subunit RNA polymerase (NEP) and a still unknown number of nuclear-encoded factors. By combining gel filtration and affinity chromatography purification steps, we isolated transcriptionally active chromosomes from Arabidopsis thaliana and mustard (Sinapis alba) chloroplasts and identified 35 components by electrospray ionization ion trap tandem mass spectrometry. Eighteen components, called plastid transcriptionally active chromosome proteins (pTACs), have not yet been described. T-DNA insertions in three corresponding genes, ptac2, -6, and -12, are lethal without exogenous carbon sources. Expression patterns of the plastid-encoded genes in the corresponding knockout lines resemble those of Drpo mutants. For instance, expression of plastid genes with PEP promoters is downregulated, while expression of genes with NEP promoters is either not affected or upregulated in the mutants. All three components might also be involved in posttranscriptional processes, such as RNA processing and/or mRNA stability. Thus, pTAC2, -6, and -12 are clearly involved in plastid gene expression.

No abstract

WRKY transcription factors are one of the largest families of transcriptional regulators found exclusively in plants. They have diverse biological functions in plant disease resistance, abiotic stress responses, nutrient deprivation, senescence, seed and trichome development, embryogenesis, as well as additional developmental and hormone-controlled processes. WRKYs can act as transcriptional activators or repressors, in various homo- and heterodimer combinations. Here we review recent progress on the function of WRKY transcription factors in Arabidopsis and other plant species such as rice, potato, and parsley, with a special focus on abiotic, developmental, and hormone-regulated processes.

Piriformospora indica, an endophytic fungus of the Sebacinaceae family, colonizes the roots of a wide variety of plant species and promotes their growth, in a manner similar to arbuscular mycorrhizal fungi. The results of the present study demonstrate that the fungus interacts also with the non‐mycorrhizal host Arabidopsis thaliana and promotes its growth. The interaction is detectable by the appearance of a strong autofluorescence in the roots, followed by the colonization of root cells by fungal hyphae and the generation of chlamydospores. Promotion of root growth was detectable even before noticeable root colonization. Membrane‐associated proteins from control roots and roots after cultivation with P. indica were separated by two‐dimensional gel‐electrophoresis and identified by electrospray ionization mass spectrometry and tandem mass spectrometry. Differences were found in the expression of glucosidase II, beta‐glucosidase PYK10, two glutathione‐S‐transferases and several so‐far uncharacterized proteins. Based on conserved domains present in the latter proteins their possible roles in plant–microbe interaction are predicted. Taken together, the present results suggest that the interaction of Arabidopsis thaliana with P. indica is a powerful model system to study beneficial plant–microbe interaction at the molecular level. Furthermore, the successful accommodation of the fungus in the root cells is preceded by protein modifications in the endoplasmatic reticulum as well as at the plasma membrane of the host.