Cell Wall Metabolism and Hexose Allocation Contribute to Biomass Accumulation in Sugarcane

Sugarcane is an emerging dual-purpose biofuel crop for energy and sugar production. It has the highest biomass production reaching 1.9 billion tonnes in 2014 worldwide. To improve sugarcane biomass accumulation, we developed an interspecific cross between Saccharum officinarum ‘LA Purple’ and Saccharum robustum ‘MOL5829’. The selected F1 individuals were self-pollinated to generate a transgressive F2 population with a wide range of biomass yields. Leaf and stem internodes of fourteen high biomass and eight low biomass F2 extreme segregants were used for RNA-seq to decipher the molecular mechanism of rapid plant growth and dry weight accumulation. Gene Ontology terms involved in cell wall metabolism and carbohydrate catabolism were enriched among 3,274 differentially expressed genes between high and low biomass groups. Specifically, up-regulation of cellulose metabolism, pectin degradation and lignin biosynthesis genes were observed in the high biomass group, in conjunction with higher transcript levels of callose metabolic genes and the cell wall loosening enzyme expansin. Furthermore, UDP-glucose biosynthesis and sucrose conversion genes were differentially expressed between the two groups. A positive correlation between stem glucose, but not sucrose, levels and dry weight was detected. We thus postulated that the high biomass sugarcane plants rapidly convert sucrose to UDP-glucose, which is the building block of cell wall polymers and callose, in order to maintain the rapid plant growth required for biomass accumulation. The gene interaction of cell wall metabolism, hexose allocation and cell division contributes to biomass yield, expanding our understanding at the molecular level required for energy cane breeding and engineering.