Golgi-Localized Mannanases Sustain Hemicellulose Biosynthesis

Abstract

O_LIMannans with {beta}-1,4-linked backbones are common cell wall components of algae and land plants. Prior challenges to enhance {beta}-mannan content in plants point to unclear metabolic bottlenecks and the potential for hidden biosynthetic players. C_LIO_LIEndo-{beta}-MANNANASEs (MANs) are the main glycosyl hydrolases that mobilize extracellular {beta}-mannans during seed germination. However, we found that Arabidopsis man2 man5 seeds resemble {beta}-mannan biosynthetic mutants. C_LIO_LICELLULOSE SYNTHASE-LIKE A (CSLA) overexpression restored {beta}-mannan synthesis in the man double mutant and increased the distribution of crystalline polymers, but impaired the release of other mucilaginous polysaccharides. C_LIO_LIUsing yeast synthetic biology, we dissected the functional interplay of MAN enzymes with CSLAs. Intracellular MAN2 and MAN5 reduced the quantity of insoluble {beta}-mannan but elevated the content of water-soluble carbohydrates. C_LIO_LIWe propose that Arabidopsis MAN2/5, and orthologous crop enzymes with a transmembrane domain, sustain hemicellulose production in the Golgi apparatus by cleaving insoluble {beta}-mannan polymers into hydrophilic counterparts. C_LI