SAITAMA, Japan, April 22, 2026 — Most of the carbon fixed by plants through photosynthesis is ultimately stored in the cell wall, primarily in the form of polysaccharides such as cellulose, xylan, and glucomannan. Yet how plants efficiently synthesize these wall polymers has remained unclear, particularly because polysaccharides such as glucomannan and xylan are prone to aggregation through hydrogen bonding and hydrophobic interactions.
A research team comprising Aina Kikuchi, who was then a master’s student in the Graduate School of Science and Engineering at Saitama University, Eriko Sato, a master’s student in the same graduate school, Associate Professor Daisuke Takahashi, Professor Toshihisa Kotake, Lecturer Yoshihisa Yoshimi of the Faculty of Biology-Oriented Science and Technology at Kindai University, and Professor Paul Dupree of the Department of Biochemistry at the University of Cambridge has discovered that mannanases (MANs)—enzymes degrading glucomannan—are also required for normal glucomannan synthesis in plants. The study shows that glucomannan biosynthesis includes an unexpected, previously unrecognized hydrolytic step in the Golgi apparatus. The work was published online in Plant Physiology on April 20, 2026 (U.S. Eastern Time).
Mannanases are enzymes that specifically cleave glucomannan. In addition to the well-known secreted type that carries an N-terminal signal peptide and functions in the cell wall, plants also possess atypical mannanases with an N-terminal transmembrane region. Because Golgi-localized atypical mannanases are widely conserved in seed plants, the team hypothesized that these proteins might play a role distinct from that of the secreted enzymes.
To test this idea, the researchers analyzed an Arabidopsis ( Arabidopsis thaliana ) double mutant lacking both MAN2 and MAN5, two atypical mannanases. Immunostaining of stem cross-sections showed that glucomannan was almost completely lost from the cell walls of the mutant plants. Biochemical analysis of soluble, alkali-extracted, and insoluble cell-wall fractions likewise revealed a marked reduction in mannose, a major sugar component derived largely from glucomannan in Arabidopsis. Immunoelectron microscopy confirmed that cell-wall glucomannan was nearly absent in the double mutant.
The team then examined whether the catalytic activity of MAN2 and MAN5 is required for this function. Introducing catalytically inactive versions of either gene into the double mutant failed to restore glucomannan accumulation, whereas introduction of the normal genes rescued the defect. These findings indicate that MAN proteins do not simply bind glucomannan during biosynthesis, but instead likely carry out hydrolytic reactions inside the Golgi while the polysaccharide is being assembled. Although their precise role remains to be determined, the researchers propose that these enzymes may help prevent aggregation of the growing glucomannan chains and thereby support normal glycan synthesis.
The discovery also suggests an evolutionary distinction in mannan biosynthesis. Mosses synthesize mannan polysaccharides but do not possess the Golgi-localized type of mannanase identified in this study, implying that mannanase-dependent hydrolysis became important specifically in seed plants. The researchers next plan to identify additional factors involved in mannan polysaccharide synthesis and to clarify how plants efficiently produce these aggregation-prone polymers. In the longer term, the findings may contribute to the development of plants that accumulate higher levels of glucomannan, an important dietary fiber.
PLANT PHYSIOLOGY
Experimental study
Cells
Atypical endo-β-1,4-mannanases are necessary for normal glucomannan synthesis in Arabidopsis
20-Apr-2026