Anna Rusaczonek

Isochorismate synthase 1 is required for thylakoid organization, optimal plastoquinone redox status, and state transitions in Arabidopsis thaliana

Isochorismate synthase 1 (ICS1) is a crucial enzyme in the salicylic acid (SA) synthesis pathway, and thus it is important for immune defences. The ics1 mutant is used in experiments on plant–pathogen interactions, and ICS1 is required for the appropriate hypersensitive disease defence response. However, ICS1 also takes part in the synthesis of phylloquinone, which is incorporated into photosystem I and is an important component of photosynthetic electron transport in plants. Therefore, photosynthetic and molecular analysis of the ics1 mutant in comparison with wild-type and SA-degrading transgenic NahG Arabidopsis thaliana plants was performed. Photosynthetic parameters in the ics1 mutant, when compared with the wild type, were changed in a manner observed previously for state transition-impaired plants (STN7 kinase recessive mutant, stn7). In contrast to stn7, deregulation of the redox status of the plastoquinone pool (measured as 1–q p) in ics1 showed significant variation depending on the leaf age. SA-degrading transgenic NahG plants targeted to the cytoplasm or chloroplasts displayed normal (wild-type-like) state transition. However, ics1 plants treated with a phylloquinone precursor displayed symptoms of phenotypic reversion towards the wild type. ics1 also showed altered thylakoid structure with an increased number of stacked thylakoids per granum which indicates the role of ICS1 in regulation of state transition. The results presented here suggest the role of ICS1 in integration of the chloroplast ultrastructure, the redox status of the plastoquinone pool, and organization of the photosystems, which all are important for optimal immune defence and light acclimatory responses.

LESION SIMULATING DISEASE 1 and ENHANCED DISEASE SUSCEPTIBILITY 1 differentially regulate UV‐C‐induced photooxidative stress signalling and programmed cell death in Arabidopsis thaliana

As obligate photoautotrophs, plants are inevitably exposed to ultraviolet (UV) radiation. Because of stratospheric ozone depletion, UV has become more and more dangerous to the biosphere. Therefore, it is important to understand UV perception and signal transduction in plants. In the present study, we show that lesion simulating disease 1 (LSD1) and enhanced disease susceptibility 1 (EDS1) are antagonistic regulators of UV-C-induced programmed cell death (PCD) in Arabidopsis thaliana. This regulatory dependence is manifested by a complex deregulation of photosynthesis, reactive oxygen species homeostasis, antioxidative enzyme activity and UV-responsive genes expression. We also prove that a UV-C radiation episode triggers apoptotic-like morphological changes within the mesophyll cells. Interestingly, chloroplasts are the first organelles that show features of UV-C-induced damage, which may indicate their primary role in PCD development. Moreover, we show that Arabidopsis Bax inhibitor 1 (AtBI1), which has been described as a negative regulator of plant PCD, is involved in LSD1-dependent cell death in response to UV-C. Our results imply that LSD1 and EDS1 regulate processes extinguishing excessive energy, reactive oxygen species formation and subsequent PCD in response to different stresses related to impaired electron transport.

Multivariable environmental conditions promote photosynthetic adaptation potential in Arabidopsis thaliana

Most of our knowledge on the regulation of photosynthesis originates from studies performed in highly controlled laboratory conditions. However, in their natural habitats plants are simultaneously subjected to a broad range of abiotic and biotic stimuli which influence photosynthetic efficiency; hence there is an emerging need to examine the process of photosynthesis under multivariable field conditions in order to elucidate the mechanisms that underlie its regulation. Such knowledge has potential for providing novel targets that would improve both crop yield and performance. In the present study we compared laboratory- and field-grown Arabidopsis thaliana plants in terms of photosynthetic efficiency in modulated light intensities and CO2 concentrations. We show here that the field-acclimated plants display highly efficient photosynthesis and are more tolerant to variable light intensities and CO2 concentrations than their laboratory-grown counterparts. We also demonstrate that some structural rearrangements of LHCII and PSII, together with altered pigments composition and stomatal density, are responsible for the differences in assimilation and photochemistry. Furthermore, we employ a transcript profiling approach to explain the genetic mechanisms underlying these adaptations and suggest that they are mainly induced by the high and fluctuating light intensities which occur in the natural environment.

Cysteine-rich receptor-like kinase CRK5 as a regulator of growth, development, and ultraviolet radiation responses in Arabidopsis thaliana

Highlight The functional characterization of Arabidopsis thaliana crk5 mutant and complementation lines reveals an essential regulatory role of this gene in ROS homeostasis, which affects senescence and abiotic stress response.

Role of phytochromes A and B in the regulation of cell death and acclimatory responses to UV stress in Arabidopsis thaliana

Highlight Phytochromes A and B are complex regulators of photosynthesis, reactive oxygen species and salicylic acid homeostasis, and UV-C-induced programmed cell death in Arabidopsis thaliana.

PHYTOALEXIN DEFICIENT 4 affects reactive oxygen species metabolism, cell wall and wood properties in hybrid aspen (Populus tremula L. × tremuloides).

The phytoalexin deficient 4 (PAD4) gene in Arabidopsis thaliana (AtPAD4) is involved in the regulation of plant--pathogen interactions. The role of PAD4 in woody plants is not known; therefore, we characterized its function in hybrid aspen and its role in reactive oxygen species (ROS)-dependent signalling and wood development. Three independent transgenic lines with different suppression levels of poplar PAD expression were generated. All these lines displayed deregulated ROS metabolism, which was manifested by an increased H2O2 level in the leaves and shoots, and higher activities of manganese superoxide dismutase (MnSOD) and catalase (CAT) in the leaves in comparison to the wild-type plants. However, no changes in non-photochemical quenching (NPQ) between the transgenic lines and wild type were observed in the leaves. Moreover, changes in the ROS metabolism in the pad4 transgenic lines positively correlated with wood formation. A higher rate of cell division, decreased tracheid average size and numbers, and increased cell wall thickness were observed. The results presented here suggest that the Populus tremula × tremuloides PAD gene might be involved in the regulation of cellular ROS homeostasis and in the cell division--cell death balance that is associated with wood development.

The dual role of LESION SIMULATING DISEASE 1 as a condition-dependent scaffold protein and transcription regulator

Since its discovery over two decades ago as an important cell death regulator in Arabidopsis thaliana, the role of LESION SIMULATING DISEASE 1 (LSD1) has been studied intensively within both biotic and abiotic stress responses as well as with respect to plant fitness regulation. However, its molecular mode of action remains enigmatic. Here, we demonstrate that nucleo-cytoplasmic LSD1 interacts with a broad range of other proteins that are engaged in various molecular pathways such as ubiquitination, methylation, cell cycle control, gametogenesis, embryo development and cell wall formation. The interaction of LSD1 with these partners is dependent on redox status, as oxidative stress significantly changes the quantity and types of LSD1-formed complexes. Furthermore, we show that LSD1 regulates the number and size of leaf mesophyll cells and affects plant vegetative growth. Importantly, we also reveal that in addition to its function as a scaffold protein, LSD1 acts as a transcriptional regulator. Taken together, our results demonstrate that LSD1 plays a dual role within the cell by acting as a condition-dependent scaffold protein and as a transcription regulator.

β-carbonic anhydrases and carbonic ions uptake positively influence Arabidopsis photosynthesis, oxidative stress tolerance and growth in light dependent manner☆

Carbonic anhydrases (CAs) catalyse reversible interconversion of CO2 and water into bicarbonate and protons and regulate concentration of CO2 around photosynthetic enzymes. In higher plants the CAs are divided into three distinct classes α, β and γ, with members off each of them being involved in CO2 uptake, fixation or recycling. The most abundant group is βCAs. In C4 plants they are localized in the cytosol of mesophyll cells and catalyse first step of carbon concentration pathway. C3 plants contain orthologues genes encoding βCAss, however their functions are unknown. Given the importance of βCAs in the present study we analysed the effect of carbonic ions, selected orthologues βCAss gene expression and βCAs enzymatic activity on Arabidopsis photosynthesis, growth and cell death in different light conditions. Plants fertilised with 0.5-3mM sodium bicarbonate had a significantly increased number of leaves, improved fresh and dry weight and reduced cell death (cellular ion leakage). This effect was dependent on provided photon flux density and photoperiod. Higher content of carbonic ions also stimulated photoprotective mechanisms such as non-photochemical quenching and foliar content of photoprotective pigments (neoxanthin, violaxanthin and carotenes). Function of various βCAs genes examined in null βcas mutants showed to be complementary and additive, and confirm results of fertilizing experiments. Taken together, regulation of βCAs gene expression and enzymatic activities are important for optimal plant growth and probably can be one of the factor influencing a switch between C3 and C4 photosynthesis mode in variable light conditions. Therefore, biotechnological amelioration of βCAs activity in economically important plants and their fertilisation with carbonic ions may lead to improved photosynthetic efficiency and further crop productivity.

Polyphenols, tannins and caffeine content and antioxidant activity of green teas coming from organic and non-organic production

Among infusions of green teabags and leafy green teas from organic and non-organic production systems we measured and compared the content of phenolic acids, flavonols and total polyphenols by spectrophotometry, the content of tannins by titration and the content of caffeine by high-performance liquid chromatography (HPLC). In addition, the antioxidant activity of the infusions was determined by spectrophotometry. The results obtained have shown that organic teas contained significantly more flavonols and tannins. However, the content of phenolic acids was higher in non-organic teas. The teas from organic and non-organic production did not differ in terms of total polyphenol content and antioxidant activity. There were no differences in leaf teas in relation to the teabags in contents of phenolic acids, tannins and total polyphenols. Organic teas had higher content of catechin C than the non-organic ones, but at the same time non-organic teas had more epigallocatechin 3-gallate (EGCG) in comparison to organic teas. Epigallocatechin (EGC) and epicatechin (EC) were not found to be different between the two groups of tea. Catechin was found to be significantly higher in teabags, while the EGCG was higher in leaf teas. The reason for this may be the oxidation of teabags, which have a greater exposed surface area. There was no appreciable effect of the form of tea on the content of tannins, caffeine, flavonols, phenolic acids, total polyphenols, EGC and EC as well as the antioxidant activity of the tea infusions examined.

ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) affects development, photosynthesis, and hormonal homeostasis in hybrid aspen (Populus tremula L. × P. tremuloides)

ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) was first described as a protein involved in salicylic acid (SA)-, ethylene-, and reactive oxygen species (ROS)-dependent defense and acclimation responses. It is a molecular regulator of biotic and abiotic stress-induced programmed cell death. Its role is relatively well known in annual plants, such as Arabidopsis thaliana or Nicotiana benthamiana. However, little is known about its functions in woody plants. Therefore, in this study, we aimed to characterize the function of EDS1 in the Populus tremula L. × P. tremuloides hybrid grown for several seasons in the natural environment. We used two transgenic lines, eds1-7 and eds1-12, with decreased EDS1 expression levels in this study. The observed changes in physiological and biochemical parameters corresponded with the EDS1 silencing level. Both transgenic lines produced more lateral shoots in comparison to the wild-type (WT) plants, which resulted in the modification of tree morphology. Photosynthetic parameters, such as quantum yield of photosystem II (ϕPSII), photochemical and non-photochemical quenching (qP and NPQ, respectively), as well as chlorophyll content were found to be increased in both transgenic lines, which resulted in changes in photosynthetic efficiency. Our data also revealed lower foliar concentrations of SA and ROS, the latter resulting most probably from more efficient antioxidant system in both transgenic lines. In addition, our data indicated significantly decreased rate of leaf senescence during several autumn seasons. Transcriptomic analysis revealed deregulation of 2215 and 376 genes in eds1-12 and eds1-7, respectively, and also revealed 207 genes that were commonly deregulated in both transgenic lines. The deregulation was primarily observed in the genes involved in photosynthesis, signaling, hormonal metabolism, and development, which was found to agree with the results of biochemical and physiological tests. In general, our data proved that poplar EDS1 affects tree morphology, photosynthetic efficiency, ROS and SA metabolism, as well as leaf senescence.