Polyamines: Α bioenergetic smart switch for plant protection and development

The present review highlights the bioenergetic role of polyamines in plant protection and development and proposes a universal model for describing polyamine-mediated stress responses. Any stress condition induces an excitation pressure on photosystem II by reforming the photosynthetic apparatus. To control this phenomenon, polyamines act directly on the molecular structure and function of the photosynthetic apparatus as well as on the components of the chemiosmotic proton-motive force (ΔpH/Δψ), thus regulating photochemical (qP) and non-photochemical quenching (NPQ) of energy. The review presents the mechanistic characteristics that underline the key role of polyamines in the structure, function, and bioenergetics of the photosynthetic apparatus upon light adaptation and/or under stress conditions. By following this mechanism, it is feasible to make stress-sensitive plants to be tolerant by simply altering their polyamine composition (especially the ratio of putrescine to spermine), either chemically or by light regulation

Structural and functional dynamic effects of polyamines in both the photodevelopment and photoadaptation of the photosynthetic apparatus

Photosynthesis comprises nowadays a wide and most active research field. This incomparable plant process constitutes not only the primary basis for sustaining plant life, but also a primary source for supporting life earth wide, since it comprises the only pathway for introducing the sunlight energy needed to the living organisms for biomass production. The processes of chloroplast photodevelopment, and photoadaptation of the photosynthetic apparatus are considered to be most important for the structural and functional integrity of the photosynthetic performance. The chloroplast photodevelopment is a dynamic process triggering the “building” of the photosynthetic apparatus and thus the basis for photosynthesis, whereas photoadaptation permits the fine tuning of the stucture and function of the developed photosynthetic apparatus, by both exploiting the environmental conditions the best way, and at the same time being able to protect itself from any putative harmfull environmental conditions. The three main polyamines (Put, Spd, Spm) were found to be localized in the chloroplast, whereas most importantly they were found to be attached to photosynthetic subcomplexes [Kotzabasis et al., 1993; del Duca et al., 1994]. Furthermore, their role in the chloroplast was associated with drastic prosseces, such as the stabilization of chlorophyll -protein complexes [Besford et al., 1993] and the inhibition of the light-independent chlorophyll biosynthesis [Beigbeder and Kotzabasis, 1994]. Thus, the present dissertation aimed to the dissection of the role of polyamines in the dynamic processes of the photodevelopment and photoadaptation of the photosynthetic apparatus. For the purpose of the experimentation the wild type strain of the unicellular green alga (Chlorophycae) Scenedesmus obliquus was used and also its mutant strains C-2A’ and C-6D, since the three strains comprise different levels of the chloroplast developmental stage. The results showed that polyamines, and especially Put are readily being regulated by onset of light and this process promotes the gradual decline of both their intracellular and intraplastidal concentrations, beginning with an oscillatory pattern. The primary photoreceptor for this regulation was identified as the “active” Protochlorophyllide, which also comprises the primary photoreceptor for chlorophyll biosynthesis and chloroplast photodevelopment. Thus, polyamine regulation and chloroplast photodevelopment share the shame photoreceptor. Other components of the signaling pathway leading to the polyamine regulation by light are heterotrimeric G-proteins, cyclic nucleotides (cNMPs), protein kinases protein phosphatases, calmodulin and Ca2+. The studied pathway reveals similarity to the pathway leading to the photosynthetic gene expression. Thus, polyamines seem to play a central role in the pathway which coordinates the chlorophyll and appoprotein biosynthesis, for the concerted development of the photosynthetic constituents. In parallel, whereas the development of the photosynthetic apparatus is still ongoing, the newly assembled Photosystem II subcomplexes trigger a second regulation of polyamine levels, by means of increasing their bound levels to the major antenna complex of PSII, the LHCII. LHCII has a unique role in photoadaptation processes, by readily adjusting its size, as a response to the changing light intensities. By externally manipulating the polyamine levels, an indisputable relation was found between the LHCII size and polyamine levels: low Put or increased Spm levels promote increase in the LHCII size, simulating low light conditions, whereas, increased Put concentration produces a smaller LHCII antenna size, an effect normally seen in high light conditions. Further dissection on the effect of polyamines in the polymerization/apopolymerization of LHCII, showed that Put and Spm affect the autoproteolytic properties of LHCII, thus modifying its size independently of the environmental light conditions Other studies performed in the laboratory of Plant Biochemistry and Photobiology (Univ. of Crete, dep. Biology) revealed the participation of the LHCII size regulation in plant photosynthetic responses to many different environmental stressors, such as high ozon concentration [Navakoudis et al., 2003] (study performed with the contribution of the GSF-Research Center (Munich), UVB radiation [Navakoudis et al., in preparation; Sfichi et al., 2004], high CO2 [Logothetis et al., 2004). In all these cases, externally manipulated polyamine concentrations were effective in reversing the sensitivity of the photosynthetic apparatus to the stressor. Thus, polyamines play a major role in regulating the LHCII size status and concomitantly the photosynthetic efficiency, thus increasing plant production under unfavourable environmental conditions.Η φωτοσύνθεση και οι επιμέρους λειτουργίες στις οποίες συνίσταται, αποτελούν ένα ευρύ και διαρκώς ανοιχτό ερευνητικό πεδίο. Η τόσο σημαντική αυτή λειτουργία για τη διαβίωση των φυτών, συγκεντρώνει το ερευνητικό ενδιαφέρον, διότι σ΄ αυτή στηρίζεται, είτε άμεσα είτε έμμεσα, η διατήρηση της ζωής στον πλανήτη, αφού μέσω της φωτοσύνθεσης επιτυγχάνεται η είσοδος της ηλιακής ενέργειας στη ζώσα ύλη για την παραγωγή βιομάζας. Ιδιαίτερα σημαντικές για τη λειτουργία της φωτοσύνθεσης είναι, αφ’ ενός η ικανότητα της ανάπτυξης του φωτοσυνθετικού μηχανισμού, στη δομική και λειτουργική οργάνωση του οποίου στηρίζεται η ίδια η φωτοσύνθεση, και αφ’ ετέρου η ικανότητα της προσαρμογής του στις διαρκώς μεταβαλλόμενες συνθήκες του περιβάλλοντος (βραχυπρόθεσμες και μακροπρόθεσμες), έτσι ώστε να επιτυγχάνεται τόσο η βέλτιστη εκμετάλλευση των περιβαλλοντικών συνθηκών προς όφελος της φωτοσύνθεσης, αλλά και η προστασία του ίδιου του φωτοσυνθετικού μηχανισμού και ως εκ τούτου η εξασφάλιση της εύρυθμης λειτουργίας του. Οι δύο αυτές επιμέρους διαδικασίες, η φωτοανάπτυξη και η φωτοπροσαρμογή του φωτοσυνθετικού μηχανισμού, αποτέλεσαν αντικείμενο της παρούσας ερευνητικής εργασίας. Με δεδομένη της ύπαρξη των τριών κύριων πολυαμινών (Put, Spd, Spm) στον χλωροπλάστη, και μάλιστα τη σύνδεσή τους με υποσύμπλοκα του φωτοσυνθετικού μηχανισμού [Kotzabasis et al., 1993; Del Duca et al.,1994], αλλά και τις διαρκώς αυξανόμενες ενδείξεις για την ανάληψη δραστικότατων ρόλων από τις πολυαμίνες στη διατήρηση/τροποποίηση ζωτικών για το φωτοσυνθετικό μηχανισμό λειτουργιών (σταθεροποίηση πρωτεϊνών και χλωροφυλλών [Besford et al., 1993], αναστολή της φωτοανεξάρτητης μετατροπής του πρωτοχλωροφυλλιδίου [Beigbeder and Kotzabasis, 1994]), η παρούσα μελέτη εστιάστηκε στην αποσαφήνιση του ρόλου των πολυαμινών στις διαδικασίες της φωτοανάπτυξης του χλωροπλάστη και της φωτοπροσαρμογής του φωτοσυνθετικού μηχανισμού. Για τους σκοπούς της μελέτης χρησιμοποιήθηκε ο άγριος τύπος του μονοκύτταρου χλωροφύκους Scenedesmus obliquus, καθώς και τα μεταλλαγμένα στελέχη αυτού, C-2A’ και C-6D, που από κοινού συνιστούν μια κλιμακούμενη διαφοροποίηση στο αναπτυξιακό στάδιο του χλωροπλάστη. Τα αποτελέσματα έδειξαν πως τo πρότυπο των ποιοτικών και ποσοτικών μεταβολών των πολυαμινών, και ειδικότερα της Put, που επάγονται, τόσο σε κυτταρικό, όσο και σε πλαστιδιακό επίπεδο, στο φως, κατά τη διαδικασία σχηματισμού του φωτοσυνθετικού μηχανισμού, εμφανίζει μια ταλαντωτική πτώση, η οποία σηματοδοτείται από τον ίδιο φωτοϋποδοχέα (ενεργό πρωτοχλωροφυλλίδιο) που ρυθμίζει τη βιοσύνθεση των χλωροφυλλών και κατ’ επέκταση τη φωτοανάπτυξη του χλωροπλάστη

A perspective on the major light-harvesting complex dynamics under the effect of pH, salts, and the photoprotective PsbS protein

The photosynthetic apparatus is a highly modular assembly of large pigment-binding proteins. Complexes called antennae can capture the sunlight and direct it from the periphery of two Photosystems (I, II) to the core reaction centers, where it is converted into chemical energy. The apparatus must cope with the natural light fluctuations that can become detrimental to the viability of the photosynthetic organism. Here we present an atomic scale view of the photoprotective mechanism that is activated on this line of defense by several photosynthetic organisms to avoid overexcitation upon excess illumination. We provide a complete macroscopic to microscopic picture with specific details on the conformations of the major antenna of Photosystem II that could be associated with the switch from the light-harvesting to the photoprotective state. This is achieved by combining insight from both experiments and all-atom simulations from our group and the literature in a perspective article

Dual pathway for metabolic engineering of Escherichia coli to produce the highly valuable hydroxytyrosol.

One of the most abundant phenolic compounds traced in olive tissues is hydroxytyrosol (HT), a molecule that has been attributed with a pile of beneficial effects, well documented by many epidemiological studies and thus adding value to products containing it. Strong antioxidant capacity and protection from cancer are only some of its exceptional features making it ideal as a potential supplement or preservative to be employed in the nutraceutical, agrochemical, cosmeceutical, and food industry. The HT biosynthetic pathway in plants (e.g. olive fruit tissues) is not well apprehended yet. In this contribution we employed a metabolic engineering strategy by constructing a dual pathway introduced in Escherichia coli and proofing its significant functionality leading it to produce HT. Our primary target was to investigate whether such a metabolic engineering approach could benefit the metabolic flow of tyrosine introduced to the conceived dual pathway, leading to the maximalization of the HT productivity. Various gene combinations derived from plants or bacteria were used to form a newly inspired, artificial biosynthetic dual pathway managing to redirect the carbon flow towards the production of HT directly from glucose. Various biosynthetic bottlenecks faced due to feaB gene function, resolved through the overexpression of a functional aldehyde reductase. Currently, we have achieved equimolar concentration of HT to tyrosine as precursor when overproduced straight from glucose, reaching the level of 1.76 mM (270.8 mg/L) analyzed by LC-HRMS. This work realizes the existing bottlenecks of the metabolic engineering process that was dependent on the utilized host strain, growth medium as well as to other factors studied in this work