Using Natural Plant Cell Wall Degradation Mechanisms to Improve Second Generation Bioethanol

Abstract

Cell wall hydrolysis is one of the key processes needed for development of the technology for second-generation (2G) bioethanol production. Thus, finding and characterizing enzymes that can deal with the complexity of the walls has been the main focus of research. As a result, data on pretreatments of many kinds and performances of enzyme cocktails containing glycosyl hydrolases from microorganisms are becoming quickly available. Here we propose that the efficiency of the 2G process could be increased even further by acquiring control of mechanisms that plants themselves use to degrade their own walls, so that wall loosening provoked by such processes would decrease the energy demand for pretreatments and facilitate hydrolysis. The examined in this chapter are plant-microorganism interaction, cell wall storage mobilization, fruit ripening, abscission, and aerenchyma formation. These systems are seen as having in common the use of modules that are coupled sequentially in order to lead to cell wall modification, including hydrolysis, for performance of different biological functions. These modules are (1) target cells perception of a message from the hormonal balance, (2) cell separation, (3) cell expansion, (4) programmed cell death, (5) hemicellulose-cellulose relaxation/hydrolysis and (6) cellulose hydrolysis. We propose that the use of synthetic biology to transform bioenergy feedstocks could be a route to increase the efficiency of 2G processes. IntroductionThe main bioethanol producers in the world are the US and Brazil, the former producing it from maize starch and the second from sucrose from sugarcane culms. In order to increase bioethanol production without increasing acreage, second

Newly identified miRNAs may contribute to aerenchyma formation in sugarcane roots

“…All of the hydrolysis modules (cell expansion, cell separation, hemicellulose, and cellulose hydrolyzes) directly related to the cell wall (Grandis et al, ) are predicted to be targeted by miRNAs (Table ). Cell separation, which comprises pectin hydrolysis, presented the highest number and diversity of predicted targets (50%), followed by hemicellulose hydrolysis (22.4%), cellulose modifications (15.5%), and cell expansion (12.1%).…”

“…It has been hypothesized that cell wall modifications rely on a general succession of events named modules (Grandis et al, ). Here, we observed that cell wall organization or biogenesis and carbohydrate metabolic process were well‐represented ontology categories among putative miRNA target genes (Figure and Table ).…”

“…Cell separation encompasses half of the targeted cell wall‐related transcripts (Table ) and mostly relies on pectin degradation (Grandis et al, ; Leite et al, ; Tavares et al, ). This module includes carbohydrate‐active enzymes such as glycosyl hydrolases, esterases, and lyases (Grandis et al, , ).…”

“…All of the hydrolysis modules (cell expansion, cell separation, hemicellulose, and cellulose hydrolyzes) directly related to the cell wall (Grandis et al, 2014) are predicted to be targeted by miRNAs F I G U R E 3 Distribution of the number of shared and exclusive expressed miRNAs during aerenchyma formation in sugarcane root segments (S1 to S4) F I G U R E 4 Hierarchical heatmap clustering miRNA expression level along with the sugarcane root segments during aerenchyma formation (S1 to S4). Blue boxes enclose the four major expression clusters (Table 2).…”

“…This is followed by cell expansion and separation, programmed cell death, and hemicellulose and cellulose hydrolysis. Each step configures a conserved set of pathways-named "modules"-shared between other endogenous cell wall degradation events (Grandis, Souza, Tavares, & Buckeridge, 2014;Tavares et al, 2015). Although cell wall changes are subtle and sugarcane pectin content is rather low (De Souza, Leite, Pattathil, Hahn, & Buckeridge, 2013), the effects of partial pectin degradation within plant tissues, especially in the middle lamella, may be quite relevant for saccharification and bioenergy production (Latarullo, Tavares, Maldonado, Leite, & Buckeridge, 2016).…”