Mixed-linkage glucan (MLG) is a component of the cell wall (CW) of grasses and is composed of glucose monomers linked by β-1,3 and β-1,4 bonds. MLG is believed to have several biological functions, such as the mobilizable storage of carbohydrates and structural support of the CW. The extracellular levels of MLG are largely controlled by rates of synthesis mediated by cellulose synthase-like (CSL) enzymes, and turnover by lichenases. Economically important crops like sorghum accumulate MLG to variable levels during development. While in sorghum, like other grasses, there is one major MLG synthase (CSLF6), the identity of lichenases is yet unknown. To fill this gap, we identified three sorghum lichenases (SbLCH1-3) and characterized them in leaves in relation to the expression of SbCSLF6, and the abundance of MLG and starch. We established that SbLCH1-3 are secreted to the apoplast, consistent with a role of degrading MLG extracellularly. Furthermore, while SbCSLF6 expression was associated with cell development, the SbLCH genes exhibited distinct development-, cell-type-specific and diel-regulated expression. Therefore, our study identifies three functional sorghum MLG lichenases and highlights that MLG accumulation in sorghum leaves is likely controlled by the activity of lichenases that tune MLG levels, possibly to suit distinct cell and developmental needs in planta. These findings have important implications for improving the growth, yield, and composition of sorghum as a feedstock.

Identification of Mixed-linkage glucan Lichenases in Sorghum bicolor has Implications for Manipulating Digestibility and Nutritional Value

AgBioResearch MICL02598

Department of Energy - Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science DE-FG02-91ER20021

Department of Energy - Great Lakes Bioenergy Research Center DE-SC0018409