Lignin in species of the genus Saccharum spp

Author(s)

Juan Pablo Portilla Llerena

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2016-06-02

Examining board members

Paulo Mazzafera; Camila Caldana; Michael dos Santos Brito

• Advisor: Paulo Mazzafera

Abstract

Sugarcane ranks among the most efficient plants when it comes to collecting and converting sunlight into chemical energy, displaying a high capacity to accumulate biomass. With the advent of second generation ethanol (2GE), otherwise known as lignocellulosic ethanol, the bagasse has received a lot of attention as raw material for the production of said biofuel. Its use, however, poses great challenges, especially because the cane¿s biomass is lignified (~23%), which limits the saccharification process. Therefore, the study of the factors that govern the cell wall¿s recalcitrance in plants that present characteristics of bioenergy is relevant to the development of hybrid kinds of cane in bioenergetics programs in order to maximize the production of 2GE. The objective of this research has been to study biosynthesis of lignin in the Saccharum spontaneum. Saccharum officinarum, Saccharum robustum and Saccharum barberi species through the identification of genes of the biosynthetic pathway of lignin and the analysis of the components of the cell wall in bot new (second + third) and mature (eighth) internodes. In this study, the content of both structural and non-structural carbohydrates has been contrasting between the different species, since both S. officinarum and S. barberi had a larger accumulation of total soluble sugars, while S. spontaneum and S. rubustum had a larger deposition of structural polysaccharides. S. spontaneum presented a noticeable accumulation of starch in comparison with other species of Saccharum. S. spontaneum and S. robustum presented the largest glucose content, while the xylose was more abundant in S. officinarum and S. barberi. The determination of the lignin content, in addition to histochemical tests with lignin-specific dyes, has confirmed the larger deposition of this polymer in the mature internodes of the four studied species, the lignification process being more accentuated in S. officinarum e S. barberi. The S/G ratio and the saccharification percentage in mature internodes were smaller in S. spontaneum and S. robustum than in S. officinarum and S. barberi, and presented no correlation, that is, the bigger presence of S units did not translate into a higher saccharification ratio. From the analysis of the profile of the oligomers by UPLC/MS it was possible to identify 11 structures between aldehydes, monomers and trimers. Independently from the internodes¿ age, S. spontaneum and S. robustum possess the largest variety and frequency of oligomers when compared to S. officinarum and S. barberi. The analysis through 2D HSQC NMR spectroscopy has brought evidence that S. officinarum and S. barberi possess a larger percentage of p-hydroxycinnamates (p-coumarate and ferulate) and acetyl substituent groups (C-3 position and total). 13 unigenes in total have been identified in the Saccharum species, which were: 1 COMT, 1 HCT, 1 F5H, 2 4CLs, 3 CAD, 1 C3H, 1 C4H, 2 CCoAOMT and 1 CCR. The analysis of the phylogenetic trees revealed that the sequences of enzymes from the Saccharum species¿ lignin¿s biosynthetic pathway grouped preferentially with its orthologs of Sorghum bicolor, Zea mays and sugarcane (the most closely related to the Saccharum gender in the Andropogoneae tribe) into clades always supported by high bootstrap values. The identified genes presented high homology between themselves and with commercial hybrids (Bottcher et al., 2013). Thus, the results show that there is conservation of genes between species and hybrids, but their regulation influences somehow both the content and the kind of lignin. Expression analysis weren¿t made in this study, but the results show nevertheless the importance of studying the transcription factors in the control of lignin biosynthesis, which could explain the variations found in both content and composition of this polymer in the cell wall (AU)

• FAPESP's process: 14/25994-1 - Lignin in species of the genus Saccharum
• Grantee: Juan Pablo Portilla Llerena
• Support Opportunities: Scholarships in Brazil - Master