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Rare Sugars: Recent Advances and Their Potential Role in Sustainable Crop Protection

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Rare Sugars: Recent Advances and Their Potential Role in Sustainable Crop Protection molecules Review Rare Sugars: Recent Advances and Their Potential Role in Sustainable Crop Protection Nikola Mijailovic 1,2, Andrea Nesler 2 , Michele Perazzolli 3,4 , Essaid Aït Barka 1 and Aziz Aziz 1,* 1 Induced Resistance and Plant Bioprotection, USC RIBP 1488, University of Reims, UFR Sciences, CEDEX 02, 51687 Reims, France; [email protected] (N.M.); [email protected] (E.A.B.) 2 Bi-PA nv, Londerzee l1840, Belgium; [email protected] 3 Department of Sustainable Agro-Ecosystems and Bioresources, Research and Innovation Centre, Fondazione Edmund Mach, 38010 San Michele all’Adige, Italy; [email protected] 4 Center Agriculture Food Environment (C3A), University of Trento, 38098 San Michele all’Adige, Italy * Correspondence: [email protected]; Tel.: +33-326-918-525 Abstract: Rare sugars are monosaccharides with a limited availability in the nature and almost unknown biological functions. The use of industrial enzymatic and microbial processes greatly reduced their production costs, making research on these molecules more accessible. Since then, the number of studies on their medical/clinical applications grew and rare sugars emerged as potential candidates to replace conventional sugars in human nutrition thanks to their beneficial health effects. More recently, the potential use of rare sugars in agriculture was also highlighted. However, overviews and critical evaluations on this topic are missing. This review aims to provide the current knowledge about the effects of rare sugars on the organisms of the farming ecosystem, with an emphasis on their mode of action and practical use as an innovative tool for sustainable agriculture. Some rare sugars can impact the plant growth and immune responses by affecting metabolic homeostasis and the hormonal signaling pathways. These properties could be used for the Citation: Mijailovic, N.; Nesler, A.; Perazzolli, M.; Aït Barka, E.; Aziz, A. development of new herbicides, plant growth regulators and resistance inducers. Other rare sugars Rare Sugars: Recent Advances and also showed antinutritional properties on some phytopathogens and biocidal activity against some Their Potential Role in Sustainable plant pests, highlighting their promising potential for the development of new sustainable pesticides. Crop Protection. Molecules 2021, 26, Their low risk for human health also makes them safe and ecofriendly alternatives to agrochemicals. 1720. https://doi.org/10.3390/ molecules26061720 Keywords: rare sugars; crop protection; resistance inducers; plant immunity; biobased pesticides; sustainable agriculture Academic Editor: George Fleet Received: 17 February 2021 Accepted: 16 March 2021 1. Introduction Published: 19 March 2021 Monosaccharides can be found in a large variety of stereoisomer forms in the nature. Isomers such as D-glucose and D-fructose, the classical examples of natural sugars, are Publisher’s Note: MDPI stays neutral exceptions as they exist in great abundance. However, the vast majority of their stereoiso- with regard to jurisdictional claims in published maps and institutional affil- mers are hard to isolate from natural sources or to synthesize chemically owning to their iations. complex structures [1,2]. According to the definition of the International Society of Rare Sugars (ISRS), such carbohydrates represent a group of different monosaccharides and their derivatives that are found in low abundance in nature and they are called rare sugars [3–5]. A list of 42 known monosaccharides has been compiled [5]. Some of them can be produced while others are already present in the nature. The list comprises 24 hexoses, 12 pentoses Copyright: © 2021 by the authors. and 6 tetroses, half of them with D-configuration and half with L-configuration. Only Licensee MDPI, Basel, Switzerland. 7 out of these 42 monosaccharides are considered as nonrare sugars, such as D-glucose, This article is an open access article distributed under the terms and D-fructose, D-galactose, D-mannose, D-ribose, D-xylose and L-arabinose [6]. Thus, twenty conditions of the Creative Commons hexoses (including D-allulose, D-allose, D-sorbose and D-tagatose) and nine pentoses Attribution (CC BY) license (https:// (including D-lyxose, L-xylulose, and D-xylitol) have been classified as rare sugars by the creativecommons.org/licenses/by/ ISRS [7,8]. Moreover, disaccharides can be produced from the listed sugars, which may 4.0/). differ depending on the type of monosaccharide and the position of the glycosidic bond. Molecules 2021, 26, 1720. https://doi.org/10.3390/molecules26061720 https://www.mdpi.com/journal/molecules Molecules 2021, 26, x FOR PEER REVIEW 2 of 21 Molecules 2021, 26, 1720 sugars by the ISRS [7,8]. Moreover, disaccharides can be produced from the listed sugars,2 of 21 which may differ depending on the type of monosaccharide and the position of the gly- cosidic bond. Examples of rare disaccharides are turanose, leucrose, isomaltulose, kojibi- Examplesose, nigerose, of rare isomaltose, disaccharides soph areorose, turanose, laminaribiose leucrose, and isomaltulose, gentiobiose kojibiose,[9]. Due to nigerose, the low isomaltose,quantity and sophorose, availability laminaribiose in nature, knowledge and gentiobiose about the [9]. ecological Due to the role low and quantity effect of and rare availabilitysugars on inliving nature, organisms knowledge remained about scarce the ecological [10,11]. roleThis and lack effect raises of the rare question sugars on of livingwhether organisms rare sugars remained have a biol scarceogical [10 ,function11]. This [9]. lack For raises example, the questionD-trehalose of whetheris a nonreduc- rare sugarsing disaccharide have a biological known functionto serve as [9]. the For main example, sugar D-trehalosecomponent of is hemolymph a nonreducing in insects disac- charide[12] and known as a potential to serve signal as the metabolite main sugar in componentyeast and plants of hemolymph during exposure in insects to biotic [12] and and asabiotic a potential stresses signal [13–16]. metabolite in yeast and plants during exposure to biotic and abiotic stressesOne [13 of–16 the]. major obstacles limiting the use of rare sugars, in addition to their low availability,One of the is the major limited obstacles and quite limiting expensiv the usee synthesis of rare methods. sugars, in Izumori addition and to colleagues their low availability,developed a is methodology the limited and for quite the cost- expensive and time-e synthesisffective methods. production Izumori of rare and sugars, colleagues called developed a methodology for the cost- and time-effective production of rare sugars, called Izumoring (Figure 1) [3]. This includes the production process of ketohexoses, aldohex- Izumoring (Figure1)[ 3]. This includes the production process of ketohexoses, aldohexoses oses and hexitols using enzymatic and microbiological reactions [3,4]. In short, isomerases and hexitols using enzymatic and microbiological reactions [3,4]. In short, isomerases are are used to equilibrate aldoses with their corresponding keto forms, and aldoses are re- used to equilibrate aldoses with their corresponding keto forms, and aldoses are reduced duced to their corresponding polyols by catalytic hydrogenation. Microbial oxidation is to their corresponding polyols by catalytic hydrogenation. Microbial oxidation is used to used to transform polyols into single ketoses and the enzymatic epimerization of ketoses transform polyols into single ketoses and the enzymatic epimerization of ketoses yields yields epimeric ketoses [17]. The Izumoring strategy combines the microbial oxidation of epimeric ketoses [17]. The Izumoring strategy combines the microbial oxidation of poly- polyols to their corresponding ketoses, which is followed by the subsequent epimerization ols to their corresponding ketoses, which is followed by the subsequent epimerization by D-tagatose-3-epimerase [18–20]. D-tagatose-3-epimerase is used to interconvert any ke- by D-tagatose-3-epimerase [18–20]. D-tagatose-3-epimerase is used to interconvert any tohexoses that are epimeric at carbon-3 location [4,5]. Polyol dehydrogenase is then used ketohexoses that are epimeric at carbon-3 location [4,5]. Polyol dehydrogenase is then used toto catalyzecatalyze oxidation–reduction oxidation–reduction reactionsreactions betweenbetween ketohexosesketohexoses andand the the corresponding corresponding hexitolshexitols [[21].21]. Furthermore, Furthermore, the the stereochemical stereochemical arrangement arrangement plays plays a role a role because because oxidases oxi- dasesderived derived from fromdifferent different microorganisms microorganisms have have different different configurational configurational requirements requirements for foroxidation. oxidation. FigureFigure 1. 1. Strategy for for interconversion interconversion of of all all the the monosaccharides monosaccharides developed developed by byIzumori Izumori group; group; modifiedmodified from from Best Best et et al. al. [ 17[17].]. Gluconobacter thailandicus InIn the the Izumoring Izumoring system, system, four four different different microorganisms microorganisms ( (Gluconobacter thailandicus,, Enterobacter aerogenes, Klebsiella pneumoniae and Enterobacter agglomerans) are used [22–24], Enterobacter aerogenes, Klebsiella pneumoniae and Enterobacter agglomerans) are used [22–24], whereby all ketohexoses, aldohexoses and hexitols are linked to make a symmetric ring whereby all ketohexoses, aldohexoses and hexitols are linked to make a symmetric
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