Chloroplast protease/chaperone AtDeg2 influences cotyledons opening and reproductive development in Arabidopsis

AtDeg2 is a chloroplast protein with dual protease/chaperone activity. Since data on how the individual activities of AtDeg2 affect growth and development of Arabidopsis thaliana plants is missing, two transgenic lines were prepared that express mutated AtDeg2 versions that have either only protease or chaperone activity and a comprehensive ontogenesis stage-based study was performed comprising wild type (WT) plants and insertional mutants that do not express AtDeg2, as well as the two transgenic lines. The repression of both AtDeg2 activities in deg2-3 mutants altered just a few phenotypic traits including the time when cotyledons were fully opened, the time when 10% flowers were open as well as the number of inflorescence branches and seed length in plants which have completed their generative development. It was demonstrated that complete opening of cotyledons as well as the number of inflorescence branches and seed length in plants which have completed their generative development required involvement of both AtDeg2 activities, whereas the time when 10% of flowers were open was controlled by AtDeg2 protease activity. These results show for the first time that the chaperone activity of AtDeg2 is needed for some elements of generative development of A. thaliana plants to proceed normally. So far, the chaperone activity of AtDeg2 was confirmed based on in vitro assays only

Mid-Infrared Spectroscopy Supports Identification of the Origin of Organic Matter in Soils

Spectroscopic methods combined with statistics have recently gathered substantial interest in pedological studies. Near-infrared (NIR) spectroscopy has been utilized, for example, for reconstructions of the history and transformations of Chernozems, although no similar research was conducted based on mid-infrared (MIR). In this paper, the relevance of MIR spectroscopy was tested in studies on the origin/affinity of organic matter from chernozemic soils. Samples collected from three vegetation classes (grasslands, forests and arable lands) were investigated using MIR spectroscopy in order to create a statistical model, which was applied on buried profiles of unknown origin. The results showed a clear disjunction of vegetation classes. Samples of buried soil were placed in the space between all classes, indicating the relation to variable vegetation. Therefore, arable lands should not be omitted in paleoecological reconstructions, because we cannot exclude the cultivation of fertile soils before their burial. It was concluded that MIR methods may have similar applicability to NIR spectroscopy. Additionally, MIR spectra may also be discriminated according to the recognized soil type, which allows for direct reconstructions of the transformation trends in buried profiles

Arabidopsis ABA-activated kinase MAPKKK18 is regulated by protein phosphatase 2C ABI1 and the ubiquitin proteasome pathway

Phosphorylation and dephosphorylation events play an important role in the transmission of the abscisic acid signal. Although SnRK2 protein kinases and group A PP2C-type phosphatases constitute a core ABA pathway, little is known about the interplay between MAP kinases and protein phosphatases 2C in the regulation of ABA pathways. In this study, an effort was made to elucidate the role of MKKK18 in relation to ABA signaling and response. The MKKK18 knockout lines showed more vigorous root growth, decreased abaxial stomatal index, and increased stomatal aperture under normal growth conditions, compared to the control WT Col-0 line. In addition to transcriptional regulation of the MKKK18 promoter by ABA, we demonstrated by using in vitro and in vivo kinase assays that the kinase activity of MKKK18 was regulated by ABA and in response to H2O2 treatment. Analysis of the cellular localization of MKKK18 showed that the active kinase was targeted specifically to the nucleus. Notably, we identified ABI1 PP2C as a MKKK18-interacting protein, and demonstrated that ABI1 inhibited its activity. Using a cell-free degradation assay, we also established that MKKK18 was unstable and was degraded by the proteasome pathway. The rate of MKKK18 degradation was delayed in the ABI1 knockout line. Overall, we provide evidence that ABI1 regulates activity and promotes proteasomal degradation of MKKK18

A role for barley calcium-dependent protein kinase CPK2a in the response to drought

Increasing the drought tolerance of crops is one of the most challenging goals in plant breeding. To improve crop productivity during periods of water deficit, it is essential to understand the complex regulatory pathways that adapt plant metabolism to environmental conditions. Among various plant hormones and second messengers, calcium ions are known to be involved in drought stress perception and signaling. Plants have developed specific calcium-dependent protein kinases that convert calcium signals into phosphorylation events. In this study we attempted to elucidate the role of a calcium-dependent protein kinase in the drought stress response of barley (Hordeum vulgare L.), one of the most economically important crops worldwide. The ongoing barley genome project has provided useful information about genes potentially involved in the drought stress response, but information on the role of calcium-dependent kinases is still limited. We found that the gene encoding the calcium-dependent protein kinase HvCPK2a was significantly upregulated in response to drought. To better understand the role of HvCPK2a in drought stress signaling, we generated transgenic Arabidopsis plants that overexpressed the corresponding coding sequence. Overexpressing lines displayed drought sensitivity, reduced nitrogen balance index, an increase in total chlorophyll content and decreased relative water content. In addition, in vitro kinase assay experiments combined with mass spectrometry allowed HvCPK2a autophosphorylation sites to be identified. Our results suggest that HvCPK2a is a dual-specificity calcium-dependent protein kinase that functions as a negative regulator of the drought stress response in barley