Cold regulation of plastid ascorbate peroxidases serves as a priming hub controlling ROS signaling in Arabidopsis thaliana

Background Short cold periods comprise a challenge to plant growth and development. Series of cold stresses improve plant performance upon a future cold stress. This effect could be provoked by priming, training or acclimation dependent hardening. Here, we compared the effect of 24 h (short priming stimulus) and of 2 week long cold-pretreatment (long priming stimulus) on the response of Arabidopsis thaliana to a single 24 h cold stimulus (triggering) after a 5 day long lag-phase, to test Arabidopsis for cold primability. Results Three types of pretreatment dependent responses were observed: (1) The CBF-regulon controlled gene COR15A was stronger activated only after long-term cold pretreatment. (2) The non-chloroplast specific stress markers PAL1 and CHS were more induced by cold after long-term and slightly stronger expressed after short-term cold priming. (3) The chloroplast ROS signaling marker genes ZAT10 and BAP1 were less activated by the triggering stimulus in primed plants. The effects on ZAT10 and BAP1 were more pronounced in 24 h cold-primed plants than in 14 day long cold-primed ones demonstrating independence of priming from induction and persistence of primary cold acclimation responses. Transcript and protein abundance analysis and studies in specific knock-out lines linked the priming-specific regulation of ZAT10 and BAP1 induction to the priming-induced long-term regulation of stromal and thylakoid-bound ascorbate peroxidase (sAPX and tAPX) expression. Conclusion The plastid antioxidant system, especially, plastid ascorbate peroxidase regulation, transmits information on a previous cold stress over time without the requirement of establishing cold-acclimation. We hypothesize that the plastid antioxidant system serves as a priming hub and that priming-dependent regulation of chloroplast-to-nucleus ROS signaling is a strategy to prepare plants under unstable environmental conditions against unpredictable stresses by supporting extra-plastidic stress protection

Die Rolle des plastidären, antioxidativen Schutzsystems während Kurzzeitspriming durch Kälte

Reactive oxygen species (ROS) are produced as natural by-products of aerobic metabolism. The production is strongly increased by stress. They can cause damage to DNA, protein and lipids and are important signalling molecules in stress regulation and plant development. The toxic nature of ROS demands for mechanisms for detoxification. All cellular compartments are protected by a variety of antioxidant enzymes. In plants, a high proportion of ROS is produced in chloroplasts. Superoxide dismutases, ascorbate peroxidases, glutathione peroxidases and peroxiredoxins antagonize ROS levels in chloroplasts, prevent oxidative damage and restrict ROS based chloroplast-to- nucleus signalling. Experimental evidence for priming of chloroplast-to- nucleus ROS signalling by a short (24 h) 4 °C stimulus in Arabidopsis thaliana was found for the first time. In naïve plants, plastidic ROS marker (ZAT10 and BAP1) were strongly induced. A short cold pre-treatment (priming), five days prior to the chilling trigger, abolished accumulation of ZAT10 and BAP1. The influence of the plastidic antioxidant system on ROS signalling was analysed in response to short term cold priming. The priming effect on ZAT10 and BAP1 depends on a slow, but long lasting induction of the thylakoid bound ascorbate peroxidase (tAPX) initiated by the priming stimulus. Regulation of tAPX took place on the level of promotor activity and was maintained on transcript abundance and protein level. A causal relationship between the presence of tAPX and the priming effect on the plastidic ROS marker was confirmed in a tAPX knockout line. Furthermore, it was shown that the priming effect of ZAT10 and BAP1 is trigger specific. Experiments with excess light as trigger instead of cold, showed no priming specific response of the two plastidic ROS marker genes for a cold/excess light combination, as was shown for cold/cold treatments. Primability of ZAT10 was not only observed in Col-0, but additionally in two accessions from colder climate, namely Ms-0 and Kas-1. A representative of a warm habitat (Cvi-0) was not cold primable, showing that primability was lost during adaptation to this habitats. Further analysis demonstrated that priming is developmentally regulated. Young plants are not able to establish priming and the capacity for priming decreases in old plants.Reaktive Sauerstoffspezies (ROS) werden als natürliches Nebenprodukt des aeroben Stoffwechsels gebildet. Ihre Produktion wird unter Stress stark erhöht. Sie können DNA, Proteine und Lipide schädigen und sind wichtige Signalmoleküle in der Stressregulation und pflanzlichen Entwicklung. Aufgrund der toxischen Wirkung von ROS sind Mechanismen für ihre Entgiftung unerlässlich. Alle zellulären Kompartimente sind durch eine Vielzahl an antioxidativen Enzymen geschützt. In Pflanzen wird ein großer Teil an ROS in Chloroplasten gebildet. Superoxiddismutasen, Ascorbateperoxidasen, Glutathionperoxidasen und Peroxiredoxine wirken ROS entgegen, verhindern oxidativen Schaden und schränken die ROS-basierte Weiterleitung von Signalen zwischen dem Chloroplasten und dem Zellkern ein. Es wurden erstmals experimentelle Belege für Priming der ROS-basierten Weiterleitung von Signalen aus dem Chloroplasten zum Zellkern nach kurzen (24 Std) 4 °C-Stimuli in Arabidopsis thaliana gefunden. In unbehandelten Pflanzen wurden die plastidär gesteuerten ROS-Markergene ZAT10 und BAP1 stark induziert. Eine kurze Kältebehandlung (Priming) fünf Tage vor dem Kältetrigger verhindert die Induktion von ZAT10 und BAP1. Der Einfluss des plastidären antioxidativen Schutzsystems auf die ROS-Signalweiterleitung wurde untersucht. Es konnte gezeigt werden, dass der Primingeffekt auf ZAT10 und BAP1 von einer langsamen, langanhaltenden Induktion der thylakoidmembran gebundenen Ascorbateperoxidase (tAPX) abhängt, welcher vom Primingstimulus ausgelöst wurde. Die Induktion der tAPX wurde durch eine erhöhte Promotoraktivität ausgelöst. Diese wirkte sich über die Transkript- auf die Proteinebene aus. Ein kausaler Zusammenhang zwischen dem Primingeffekt auf ZAT10 und BAP1 konnte durch den Einsatz von tAPX Knockoutpflanzen bestätigt werden. Zusätzlich konnte gezeigt werden, dass der Primingeffekt auf die beiden ROS-Markergene triggerspezifisch ist. Experimente mit erhöhten Lichtbedingungen als Trigger zeigten keinen Primingeffekt auf die ROS-abhängige Signalweiterleitung, der für Kälte/Kälte- Behandlungen gezeigt werden konnte. Die Primbarkeit von ZAT10 konnte nicht nur in Col-0 festgestellt, sondern auch in zwei Akzessionen aus Regionen mit kälterem Klima nachgewiesen werden (Ms-0 und Kas-1). Eine Akzession aus einem warmen Lebensraum (Cvi-0) war im Vergleich nicht primbar. Dies zeigt, dass die Primbarkeit während der Adaptation an dieses Habitat verloren ging. Zudem zeigten weitere Analysen, dass Priming entwicklungsabhängig reguliert wird. Junge Pflanzen konnten nicht geprimt werden, in alten Pflanzen war die Primbarkeit stark reduziert

Cold-priming of chloroplast ROS signalling is developmentally regulated and is locally controlled at the thylakoid membrane

Abstract 24 h exposure to 4 °C primes Arabidopsis thaliana in the pre-bolting rosette stage for several days against full cold activation of the ROS responsive genes ZAT10 and BAP1 and causes stronger cold-induction of pleiotropically stress-regulated genes. Transient over-expression of thylakoid ascorbate peroxidase (tAPX) at 20 °C mimicked and tAPX transcript silencing antagonized cold-priming of ZAT10 expression. The tAPX effect could not be replaced by over-expression of stromal ascorbate peroxidase (sAPX) demonstrating that priming is specific to regulation of tAPX availability and, consequently, regulated locally at the thylakoid membrane. Arabidopsis acquired cold primability in the early rosette stage between 2 and 4 weeks. During further rosette development, primability was widely maintained in the oldest leaves. Later formed and later maturing leaves were not primable demonstrating that priming is stronger regulated with plant age than with leaf age. In 4-week-old plants, which were strongest primable, the memory was fully erasable and lost seven days after priming. In summary, we conclude that cold-priming of chloroplast-to-nucleus ROS signalling by transient post-stress induction of tAPX transcription is a strategy to modify cell signalling for some time without affecting the alertness for activation of cold acclimation responses

New developments in RiPP discovery, enzymology and engineering

Ribosomally-synthesized and post-translationally modified peptides (RiPPs) are a large group of natural products. A community-driven review in 2013 described the emerging commonalities in the biosynthesis of RiPPs and the opportunities they offered for bioengineering and genome mining. Since then, the field has seen tremendous advances in understanding of the mechanisms by which nature assembles these compounds, in engineering their biosynthetic machinery for a wide range of applications, and in the discovery of entirely new RiPP families using bioinformatic tools developed specifically for this compound class. The First International Conference on RiPPs was held in 2019, and the meeting participants assembled the current review describing new developments since 2013. The review discusses the new classes of RiPPs that have been discovered, the advances in our understanding of the installation of both primary and secondary post-translational modifications, and the mechanisms by which the enzymes recognize the leader peptides in their substrates. In addition, genome mining tools used for RiPP discovery are discussed as well as various strategies for RiPP engineering. An outlook section presents directions for future research