Cell- and development-specific degradation controls the levels of mixed-linkage glucan in sorghum leaves


S-J. Kim et al. "Cell-and development-specific degradation controls the levels of mixed-linkage glucan in sorghum leaves" The Plant Journal 116:360 (2023) [DOI: 10.1111/tpj.16376]


Mixed-linkage glucan (MLG) is a component of the cell wall (CW) of grasses and is composed of glucose monomers linked by beta-1,3 and beta-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.

Data Access

Data from this study are hosted by the JGI Genome Portal https://genome.jgi.doe.gov/portal/. The JGI project names and the JGI project IDs that can be used to search for the datasets are: Regulation of MLG Pathway Gene Expression Profiling, JGI Project ID: 1317812 and Sorghum bicolor Circadian Cycling Gene Expression Profiling, JGI Project ID: 1051031.