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4 páginas.- 3 figuras. 17 referencias.- Comunicación oral presentada en el 16th European Workshop on Lignocellulosics and Pulp (EWLP) Gothenburg, Sweden, June 28 – July 1, 2022, As ever more component monomers are discovered, lignin can no longer be regarded as deriving from just the three canonical monolignols. Pathway intermediates and additional products of truncated biosynthesis are now established lignin monomers. The array of acylated monolignols continues to expand. Game-changing findings have demonstrated that phenolics from alternative pathways, including flavonoids and hydroxystilbenes, are also involved in lignification, expanding the traditional concept. Beyond the basic science intrigue, these findings propound exciting new avenues for valorizing lignins, or for producing more readily extractable or depolymerizable lignins, in crop and bioenergy plants., We further acknowledge lots of colleagues and collaborators, and funding from the Swiss National Science Foundation (Synergia) grant # CRS115_180258, and the DOE Great Lakes Bioenergy Research Center (DOE BER Office of Science DE-SC0018409).

Comunicación oral presentada en la XXIX Conferencia Internacional sobre Polifenoles y la 9ª Conferencia de Taninos, del 16 al 20 de julio de 2018 Madison, WI, USA, MAIN CONCLUSION Lignin biosynthesis is uniquely malleable, allowing a variety of phenolics to be utilized as lignin monomers and therefore allowing some tailoring of its structure, reactivity, and value. We are now at a juncture where actual ‘design’ of the polymer can be contemplated and envisioning an ideal polymer for lignin valorization can be entertained. INTRODUCTION Evidence continues to mount regarding lignins’ inherent structural malleability from studies on lignin pathway mutants and transgenics as well as on various ‘natural’ plants discovered to possess unusual lignins. [1-4] Most of the monomers previously considered were from the monolignol biosynthetic pathway itself. More recently, phenolics from beyond the monolignol pathway have been shown to be authentic monomers in some plants, including the flavone tricin in all grasses (and beyond),[5,6] various hydroxystilbenes in some palm endocarp tissues,[7,8] and now possible nitrogenous compounds such a putrescine in maize kernel lignin. [9] As we have frequently noted from some time back, but not in print until 2008: “any phenolic transported to the lignifying zone of the cell wall can, subject to simple chemical compatibility, be incorporated into the polymer.”[10] That does not automatically mean that the r sulting polymer will be well tolerated by the plant, but researchers are now able to contemplate some degree of actually designing lignins for improved utilization and value, and muse over what might constitute a lignin that is ideally suited for conversion to phenolic monomers, adding value to the biorefinery. RESULTS AND DISCUSSION As José Carlos del Río will cover the other pathways that are now known to contribute to lignification, we shall provide an update to how lignins can be designed to fall apart more readily during processing (the so-called ‘zip-lignin’ approach) and describe a lignin that is natural in some tissues (but not yet in plant stems) that is one example of an ideal lignin. Zip-lignins. We have now shown that it is possible to engineer weak bonds (esters) into the lignin backbone,[11] thus facilitating lignin depolymerization during pretreatment or processing (such as in pulping).[12] It turns out that Nature is already making lignins this way, at low levels, in a variety of plants;[13] we may have even inadvertently selected for this trait in targeting woody species that pulp most easily, for example. An “ideal lignin.” It is now a realistic juncture to posit the characteristics for an “ideal lignin” archetype for biomass processing. For the depolymerization of the polymer to monomers, one ideotype is a lignin that has at least the following three characteristics. First, it should be stable under acidic conditions to prevent condensation and the generation of undesired new C–C bonds, during pretreatment. Second, it should contain only ether (C–O) inter-unit linkages in its backbone so that it can be fully depolymerized. Last, it should be generated in planta from a single phenylpropanoid monomer to allow the production of the simplest array of compounds. C-lignin, such as that found in vanilla and various cacti seed coats, [14,15] is essentially a homopolymer synthesized almost purely by β–O–4-coupling of caffeyl alcohol with the growing polymer chain, producing benzodioxanes as the dominant unit in the polymer, is an example of such an “ideal lignin” that can, in principle, be depolymerized to a single monomeric product in high yield. Here we will describe the ideal nature of this lignin via a revised compositional characterization of the vanilla seedcoat fiber, new features of the C-lignin’s reactivity and stability, and our successful attempts at converting it to monomers in near-quantitative yields., REFERENCES [1] Y. Mottiar, R. Vanholme, W. Boerjan, J. Ralph, S. D. Mansfield, Current Opinion in Biotechnology 2016, 37, 190. [2] R. Vanholme, K. Morreel, C. Darrah, P. Oyarce, J. H. Grabber, J. Ralph, W. Boerjan, New Phytologist 2012, 196, 978. [3] J. Ralph, Phytochemistry Reviews 2010, 9, 65. [4] W. Boerjan, J. Ralph, M. Baucher, Annual Review of Plant Biology 2003, 54, 519. [5] W. Lan, J. Rencoret, F. Lu, S. D. Karlen, B. G. Smith, P. J. Harris, J. C. del Rio, J. Ralph, The Plant Journal 2016, 88, 1046. [6] J. C. del Río, J. Rencoret, P. Prinsen, Á. T. Martínez, J. Ralph, A. Gutiérrez, Journal of Agricultural and Food Chemistry 2012, 60, 5922. [7] J. C. del Río, J. Rencoret, A. Gutiérrez, H. Kim, J. Ralph, Plant Physiology 2017, 174, 2072. [8] J. Rencoret, H. Kim, A. B. Evaristo, A. Gutiérrez, J. Ralph, J. C. del Río, Journal of Agricultural and Food Chemistry 2018, 66, 138. [9] J. C. del Río, J. Rencoret, A. Gutierrez, H. Kim, J. Ralph, Journal of Agricultural & Food Chemistry 2018, in press (accepted 4/20/2018). [10] J. Ralph, G. Brunow, P. J. Harris, R. A. Dixon, P. F. Schatz, W. Boerjan, in Recent Advances in Polyphenol Research, Vol. 1 (Eds.: F. Daayf, A. El Hadrami, L. Adam, G. M. Ballance), Wiley-Blackwell Publishing, Oxford, UK, 2008, pp. 36-66. [11] C. G. Wilkerson, S. D. Mansfield, F. Lu, S. Withers, J.-Y. Park, S. D. Karlen, E. Gonzales-Vigil, D. Padmakshan, F. Unda, J. Rencoret, J. Ralph, Science 2014, 344, 90. [12] S. Zhou, T. Runge, S. D. Karlen, J. Ralph, E. Gonzales-Vigil, S. D. Mansfield, ChemSusChem 2017, 10, 3565. [13] S. D. Karlen, C. Zhang, M. L. Peck, R. A. Smith, D. Padmakshan, K. E. Helmich, H. C. A. Free, S. Lee, B. G. Smith, F. Lu, J. C. Sedbrook, R. Sibout, J. H. Grabber, T. M. Runge, K. S. Mysore, P. J. Harris, L. E. Bartley, J. Ralph, Science Advances 2016, 2, e1600393. [14] F. Chen, Y. Tobimatsu, L. Jackson, J. Nakashima, J. Ralph, R. A. Dixon, The Plant Journal 2013, 73, 201. [15] F. Chen, Y. Tobimatsu, D. Havkin-Frenkel, R. A. Dixon, J. Ralph, P Natl Acad Sci USA 2012, 109, 1772., This work was funded in part by the DOE Great Lakes Bioenergy Research Center (DOE BER Office of Science DE-FC02-07ER64494 and DE-SC0018409).

The efficiency of water use to produce biomass is a key trait in designing sustainable bioenergy-devoted systems. We characterized variations in the carbon isotope composition (δ13C) of leaves, current year wood and holocellulose (as proxies for water use efficiency, WUE) among six poplar genotypes in a short-rotation plantation. Values of δ13Cwood and δ13Cholocellulose were tightly and positively correlated, but the offset varied significantly among genotypes (0.791.01). Leaf phenology was strongly correlated with δ13C, and genotypes with a longer growing season showed a higher WUE. In contrast, traits related to growth and carbon uptake were poorly linked to δ13C. Trees growing on former pasture with higher N-availability displayed higher δ13C as compared with trees growing on former cropland. The positive relationships between δ13Cleaf and leaf N suggested that spatial variations in WUE over the plantation were mainly driven by an N-related effect on photosynthetic capacities. The very coherent genotype ranking obtained with δ13C in the different tree compartments has some practical outreach. Because WUE remains largely uncoupled from growth in poplar plantations, there is potential to identify genotypes with satisfactory growth and higher WUE.

Lignin is a heteropolymer that is thought to form in the cell wall by combinatorial radical coupling of monolignols. Here, we present a simulation model of in vitro lignin polymerization, based on the combinatorial coupling theory, which allows us to predict the reaction conditions controlling the primary structure of lignin polymers. Our model predicts two controlling factors for the β-O-4 content of syringyl-guaiacyl lignins: the supply rate of monolignols and the relative amount of supplied sinapyl alcohol monomers. We have analyzed the in silico degradability of the resulting lignin polymers by cutting the resulting lignin polymers at β-O-4 bonds. These are cleaved in analytical methods used to study lignin composition, namely thioacidolysis and derivatization followed by reductive cleavage, under pulping conditions, and in some lignocellulosic biomass pretreatments.

13 pages, 4 figures, 3 tables, 51 references., Lignin engineering is a promising strategy to optimize lignocellulosic plant biomass for use as a renewable feedstock for agro-industrial applications. Current efforts focus on engineering lignin with monomers that are not normally incorporated into wild-type lignins. Here we describe an Arabidopsis line in which the lignin is derived to a major extent from a non-traditional monomer. The combination of mutation in the gene encoding caffeic acid O-methyltransferase (comt) with over-expression of ferulate 5-hydroxylase under the control of the cinnamate 4-hydroxylase promoter (C4H:F5H1) resulted in plants with a unique lignin comprising almost 92% benzodioxane units. In addition to biosynthesis of this particular lignin, the comt C4H:F5H1 plants revealed massive shifts in phenolic metabolism compared to the wild type. The structures of 38 metabolites that accumulated in comt C4H:F51 plants were resolved by mass spectral analyses, and were shown to derive from 5-hydroxy-substituted phenylpropanoids. These metabolites probably originate from passive metabolism via existing biochemical routes normally used for 5-methoxylated and 5-unsubstituted phenylpropanoids and from active detoxification by hexosylation. Transcripts of the phenylpropanoid biosynthesis pathway were highly up-regulated in comt C4H:F5H1 plants, indicating feedback regulation within the pathway. To investigate the role of flavonoids in the abnormal growth of comt C4H:F5H1 plants, a mutation in a gene encoding chalcone synthase (chs) was crossed in. The resulting comt C4H:F5H1 chs plants showed partial restoration of growth. However, a causal connection between flavonoid deficiency and this restoration of growth was not demonstrated; instead, genetic interactions between phenylpropanoid and flavonoid biosynthesis could explain the partial restoration. These genetic interactions must be taken into account in future cell-wall engineering strategies

Eleven laboratories have collaborated to study chloroplast DNA (cpDNA) variation in black poplar (Populus nigra L.) across Europe in order to improve our understanding of the location of glacial refugia and the subsequent postglacial routes of recolonisation. A common analysis based on the restricted fragments produced by five primer pairs was used to determine the cpDNA haplotype of 637 samples obtained from genebank collections established in nine European countries. Haplotype 2 was particularly common and was found in 46% of the non-hybrid samples. A total of 81 non-hybrid chloroplast variants were detected. Three haplotypes (from four trees believed to originate from Eastern Europe) clustered together and were very different from the rest of the samples. The remaining samples were divided into two groups, one of which had a largely eastern distribution and samples from the other group were mostly located in the west. This, along with the fact that Spain in the southwest and Austria and Italy in the southeast had high diversity, suggest that there were ice age refugia of black poplar in both southwestern (Spain) and southeastern Europe (Italy and/or Balkan). Results also indicate that the Pyrenees formed a significantbarrier, since only 7 of the 45 haplotypes in Spain exist elsewhere in Europe

International audience; We evaluated lignin profiles and pulping performances of 2-year-old transgenic poplar (Populus tremula × Populus alba) lines severely altered in the expression of caffeic acid/5-hydroxyferulic acidO-methyltransferase (COMT) or cinnamyl alcohol dehydrogenase (CAD). Transgenic poplars with CAD orCOMT antisense constructs showed growth similar to control trees. CAD down-regulated poplars displayed a red coloration mainly in the outer xylem. A 90% lower COMT activity did not change lignin content but dramatically increased the frequency of guaiacyl units and resistant biphenyl linkages in lignin. This alteration severely lowered the efficiency of kraft pulping. The Klason lignin level of CAD-transformed poplars was slightly lower than that of the control. Whereas CAD down-regulation did not change the frequency of labile ether bonds or guaiacyl units in lignin, it increased the proportion of syringaldehyde and diarylpropane structures and, more importantly with regard to kraft pulping, of free phenolic groups in lignin. In the most depressed line, ASCAD21, a substantially higher content in free phenolic units facilitated lignin solubilization and fragmentation during kraft pulping. These results point the way to genetic modification of lignin structure to improve wood quality for the pulp industry.