Senescence is a ubiquitous characteristic in the biological world. From an ontogenetic perspective, senescence is now established as a developmental and genetic program acquired during evolution (Wojciechowska et al., 2018). Like in other organisms, senescence in plants is genetically programmed (Nam, 1997; van Doorn and Woltering, 2004; Wojciechowska et al., 2018). In plants, senescence is a prelude to cell (organ) death, and during this process metabolites and macromolecules released are salvaged for utilization by the plant for growth. Generally, senescence occurs prior to programmed cell death (PCD), since symptomatic leaf yellowing can be reversed based on the timing of senescence while PCD is a terminal, irreversible program. It has been suggested that the term "PCD" in plants should be restricted to the specific stage of intrinsic senescence program when it has reached a "point of no return" and leaf yellowing is no longer reversible (Mattoo and Handa, 2003). Programmed cell death in plants was described as a sequential process that included apoptosis-like necrosis and autophagy (van Doorn et al., 2011). Autophagy under normal growth conditions favors turnover of cellular components for maintaining homeostasis,

Summary• The thylakoid protease Deg2 is a serine-type protease peripherally attached to the stromal side of the thylakoid membrane. Given the lack of knowledge concerning its function, two T-DNA insertion lines devoid of Deg2 were prepared to study the functional importance of this protease in Arabidopsis thaliana.• The phenotypic appearance of deg2 mutants was studied using a combination of stereo and transmission electron microscopy, and short-stress-mediated degradation of apoproteins of minor light-harvesting antennae of photosystem II (PSII) was analysed by immunoblotting in the mutants in comparison with wild-type plants.• Deg2 repression produced a phenotype in which reduced leaf area and modified chloroplast ultrastructure of older leaves were the most prominent features. In contrast to the wild type, the chloroplasts of second-whorl leaves of 4-wk-old deg2 mutants did not display features typical of the early senescence phase, such as undulation of the chloroplast envelope and thylakoids. The ability to degrade the photosystem II light-harvesting protein Lhcb6 apoprotein in response to brief high-salt, wounding, high-temperature and high-irradiance stress was demonstrated to be impaired in deg2 mutants.• Our results suggest that Deg2 is required for normal plant development, including the chloroplast life cycle, and has an important function in the degradation of Lhcb6 in response to short-duration stresses.

The EGY3 protein is a homologue of site‐2 proteases, which are intramembrane zinc metalloproteases. EGY3 itself lacks proteolytic activity due to the absence of a zinc‐binding motif. Plentiful evidence indicates that such intramembrane ‘pseudoproteases’ play significant roles in many diverse processes occurring within the cell. However, the physiological functions of EGY3, as well as its subcellular localization, remain unknown. The subcellular localization of EGY3 protein was investigated using Arabidopsis thaliana protoplasts transformed with EGY3‐GFP fusion protein, and immunoblot experiments using the total leaf protein extract, as well as highly purified chloroplasts and fractions of stroma, envelope and thylakoid membrane proteins. The physiological role of EGY3 was studied using two A. thaliana mutant lines devoid of EGY3 protein. Chlorophyll a fluorescence measurement was performed and the egy3 mutant sensitivity to photoinhibition was investigated. Additionally, the abundance of thylakoid membrane complexes was established using blue native gel electrophoresis. We present experimental evidence for thylakoid membrane localization of the EGY3 protein. We show that egy3 mutants display increased value of the non‐photochemical quenching parameter and significantly slower recovery rate after photoinhibitory treatment. This was associated with a decrease in the level of proteases involved in photosystem II recovery, Deg1 and FtsH2/8.

No abstract

The study reported was aimed at the identification and determination of the chromosomal organisation of genes involved in the ethylene biosynthesis and signalling pathways in Brassica oleracea, on the basis of the Arabidopsis thaliana DNA probes and in silico genome analysis. Because of its polyploidal origin, the B. oleracea genome is characterised by extensive gene redundancy. Therefore, an important aspect of gene expression in B. oleracea response to environmental stimuli is to identify the specific gene copy involved. This aspect should also be taken into consideration while studying the genetic basis of biosynthesis and signal transduction in relation to basic phytohormones. Our present work concerns the identification of homologue genes involved in ethylene biosynthesis such as SAM, ACS and ACO, as well as those involved in the ethylene signalling pathway, mainly ETR1, CTR1, MKK4, MKK5, EIN2, EIN3, EREBP, ERF5 and ERF7 on the basis of the restriction fragment length polymorphism (RFLP) and PCR mapping. In the case of ACC synthases, (ACSs) the in silico analysis of gene variants in the genome of A. thaliana was followed by the identification of homologues to ACS2, ACS6 and ACS7 in the B. oleracea database. In total, 22 loci with sequence homology to the genes under analysis were included in the existing B. oleracea RFLP chromosomal map. Based on the stress responsiveness of most of the A. thaliana genes analysed in this study, we performed initial functional analysis of some gene homologues mapped. With the use of the RT-PCR approach the conservation of differential transcriptional induction of ACS homologues in the B. oleracea and A. thaliana was demonstrated during ozone stress.