RT Journal Article
SR Electronic
T1 Degradation of mixed-linkage (1,3;1,4)-β-D-glucan in maize is mediated by the CAL1 licheninase
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2020.11.16.385146
DO 10.1101/2020.11.16.385146
A1 Florian J Kraemer
A1 China Lunde
A1 Moritz Koch
A1 Benjamin M Kuhn
A1 Clemens Ruehl
A1 Patrick J Brown
A1 Philipp Hoffmann
A1 Vera Göhre
A1 Sarah Hake
A1 Markus Pauly
A1 Vicente Ramírez
YR 2020
UL http://biorxiv.org/content/early/2020/11/18/2020.11.16.385146.abstract
AB The presence of mixed-linkage (1,3;1,4)-β-D-glucan (MLG) in plant cell walls is a key feature of grass species such as cereals - the main source of calorie intake for humans and cattle. Accumulation of this polysaccharide involves the coordinated regulation of biosynthetic and metabolic machineries. While several components of the MLG biosynthesis machinery have been identified in diverse plant species, degradation of MLG is poorly understood. A large-scale forward genetic maize screen for mutants with altered cell wall polysaccharide structural properties resulted in the identification of candy-leaf1 (cal1). Cell walls of CAL1-deficient plants contain higher amounts of MLG in several tissues, including adult leaves and senesced organs, where only trace amounts of MLG are usually detected. In addition, cal1 plants exhibit increased saccharification yields upon enzymatic digestion. Stacking cal1 with lignin-deficient mutations results in synergistic saccharification increases. Identification of the causative mutation revealed that CAL1 encodes a GH17 licheninase. Maize plants overexpressing CAL1 exhibit a 90% reduction in MLG content, indicating that CAL1 is not only required, but its expression sufficient to degrade MLG. CAL1 specifically hydrolyzes (1,3;1,4)-β-D-Glucans in vitro, and the single CAL1E262K amino acid substitution is able to block all detectable activity. Time profiling experiments indicate that wall MLG content is modulated during day/night cycles inversely correlating with CAL1 transcript accumulation. This cycling is absent in the cal1 mutant, suggesting that the mechanism involved requires MLG degradation that may in turn regulate CAL1 gene expression.One sentence summary Mixed-linkage glucan is degraded by the CAL1 licheninase in maize