The rimb1 (redox imbalanced 1) mutation was mapped to the RCD1 locus (radical-induced cell death 1; At1g32230) demonstrating that a major factor involved in redox-regulation genes for chloroplast antioxidant enzymes and protection against photooxidative stress, RIMB1, is identical to the regulator of disease response reactions and cell death, RCD1. Discovering this link let to our investigation of its regulatory mechanism. We show in yeast that RCD1 can physically interact with the transcription factor Rap2.4a which provides redox-sensitivity to nuclear expression of genes for chloroplast antioxidant enzymes. In the rimb1 (rcd1-6) mutant, a single nucleotide exchange results in a truncated RCD1 protein lacking the transcription factor binding site. Protein-protein interaction between full-length RCD1 and Rap2.4a is supported by H2O2, but not sensitive to the antioxidants dithiotreitol and ascorbate. In combination with transcript abundance analysis in Arabidopsis, it is concluded that RCD1 stabilizes the Rap2.4-dependent redox-regulation of the genes encoding chloroplast antioxidant enzymes in a widely redox-independent manner. Over the years, rcd1-mutant alleles have been described to develop symptoms like chlorosis, lesions along the leaf rims and in the mesophyll and (secondary) induction of extra- and intra-plastidic antioxidant defense mechanisms. All these rcd1 mutant characteristics were observed in rcd1-6 to succeed low activation of the chloroplast antioxidant system and glutathione biosynthesis. We conclude that RCD1 protects plant cells from running into reactive oxygen species (ROS)-triggered programs, such as cell death and activation of pathogen-responsive genes (PR genes) and extra-plastidic antioxidant enzymes, by supporting the induction of the chloroplast antioxidant system.

Two collections of Arabidopsis GAL4 enhancer trap lines were screened for light-intensity dependent reporter gene activation. Line N9313 was isolated for its strong light-intensity regulation. The T-DNA element trapped distant enhancers of the SIG5 promoter, which drives expression of a sigma factor involved in regulation of chloroplast genes for photosystem II core proteins. The T-DNA insertion 715 bp upstream of the transcription initiation site splits the promoter in a distal and proximal part. Both parts are sensitive to blue and red light and depend on photosynthetic electron transport activity between photosystem II and the plastoquinone pool. The mainblue-light sensitivity is localized within a 196-bp sequence (–887 to –691 bp) in the proximal promoter region It is preferentially CRY1 and PHYB controlled. Type-I and type-II phytochromes mediate red-light sensitivity via various promoter elements spread over the proximal and distal upstream region. This work characterizes SIG5 as an anterograde control factor of chloroplast gene expression, which is controlled by chloroplast signals in a retrograde manner.

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Fungicides are one possible way to manage fungal and oomycete plant pathogens in order to safeguard yield and quality of crops and to improve shelf‐life of produce in agriculture and horticulture. However, global warming and the resulting temperature increase may affect the effectiveness of some important fungicides, including efficacy and duration of plant disease control. Nevertheless, according to our literature survey, there is little specific information available on whether and how temperature influences the effectiveness of fungicides. The very few publications that show specific data are summarized herein. Specific data are mainly gained under controlled conditions, both based on in vitro and in planta experiments. Field data are more or less missing. Most researchers assume that indirect effects of temperature on fungicide efficacy are particularly important. For example, temperature effects on pathogen spore germination and hyphal growth (optimal versus sub‐ and supra‐optimal), whereby optimal temperature conditions can improve pathogen fitness, thereby increasing the tolerance of pathogens to fungicides. Presumably, these indirect effects are often more important than the direct effects of temperature on fungicide performance. However, the data needed to prove this assumption are lacking. Therefore, it would be beneficial to conduct more in‐depth laboratory, greenhouse and field experiments in order to investigate the potential direct and indirect influence of temperature on the effectiveness of important fungicides. This would enable the establishment of appropriate recommendations for fungicide use in an increasingly warmer world and would assist the development of future fungicide solutions, based on improved knowledge.