Cell wall polymer interactions, rather than polysaccharide fine structure, underlie recalcitrance in energy cane varieties.

Abstract

Second-generation bioethanol production from lignocellulosic biomass has driven the development of high-fiber sugarcane varieties known as energy canes, which combine high tillering, high biomass accumulation, lower sucrose, and improved agronomic performance. However, energy canes have been reported to be more recalcitrant to enzymatic saccharification. We compared biomass and cell wall composition, non-cellulosic polysaccharide extractability, and saccharification efficiency in two energy cane varieties, Vertix V2 and Vertix V3, and sugarcane. Sugarcane contained three times as much sucrose and less fiber than energy canes. After removing soluble sugars from the biomass, reduced digestibility became evident in the two energy cane varieties, particularly in V2. Saccharification increased with alkali and doubled after acidic sodium chlorite treatments. Although the main polysaccharides and linkage structures were broadly conserved across genotypes, minor changes were observed in their relative abundance and extractability. Glucuronoarabinoxylans (GAX) were the predominant wall polysaccharides (72%), while pectins [homogalacturonan (HG) and rhamnogalacturonan I (RG-I), each 1%], arabinan side-groups (4-6%), glucomannans (1%), and xyloglucan (2-4%) occurred in smaller proportions. Sugarcane contained higher abundances of xyloglucan, β-glucan, glucomannan, and arabinan, whereas energy canes had higher HG and RG-I. Chlorite oxidation solubilized GAX and RG-I, indicating that polymers are associated with phenylpropanoids and contribute to wall recalcitrance. The contrasting saccharification behavior of the sugarcane and energy cane varieties examined here appears to arise not from major changes in polysaccharide fine structure, but from differences in biomass allocation, phenylpropanoid abundance, extractability, and molecular interactions among cellulose, matrix polysaccharides, and phenylpropanoids within the cell wall. Understanding these properties in relation to enzyme-mediated disassembly is fundamental to accessing grass walls and improving biomass saccharification.