Surreal illustration of plant cell wall construction.

Cracking the Code of Plant Cell Walls: New Insights into Galactan Synthases

Jordan Keane in Science & Nature August 2025 • 4 min read.

"Unlocking the secrets of pectin biosynthesis could revolutionize biofuel production and plant resilience."

Plant cell walls are complex structures that provide support, protection, and shape to plant cells. Pectin, a major component of these walls, plays a crucial role in plant growth, development, and defense. Understanding how pectin is made is essential for improving plant health and utilizing plants for various applications.

Despite its importance, the biosynthesis of pectin is not fully understood. Scientists have been working to identify the enzymes involved in building these complex polysaccharides. Recent research has focused on a family of enzymes called glycosyltransferases (GTs), specifically the GT92 family in the model plant Arabidopsis thaliana.

A new study published in Plant Cell Physiology sheds light on the function of three members of the GT92 family: GALS1, GALS2, and GALS3. Researchers have found that all three enzymes are functional β-1,4-galactan synthases, responsible for adding galactose sugars to specific regions of the pectin molecule. This discovery provides valuable insights into the intricate process of plant cell wall construction and opens doors for future applications.

What are Galactan Synthases and Why Do They Matter?

Surreal illustration of plant cell wall construction.

Galactan synthases are enzymes that catalyze the addition of galactose sugars to a growing polysaccharide chain. In the case of pectin biosynthesis, galactan synthases are responsible for creating β-1,4-galactans, a type of polysaccharide found as side chains in rhamnogalacturonan-I (RG-I), a major component of pectin.

The study revealed several important characteristics of the GALS enzymes:

Enzyme Activity: All three GALS proteins (GALS1, GALS2, and GALS3) function as galactan synthases, adding galactose to existing galactose residues on the RG-I backbone.
Acceptor Preference: The enzymes exhibit a preference for longer galacto-oligosaccharides as acceptors, with galactopentaose showing significant activity but longer acceptors being favored.
In vivo Impact: Overexpression of GALS proteins in Arabidopsis leads to an accumulation of unbranched β-1,4-galactan, while inactivation of all three genes results in plants lacking detectable β-1,4-galactan.
Subcellular Localization: Like GALS1, GALS2 and GALS3 are localized to the Golgi apparatus, consistent with their role in pectin biosynthesis.

Surprisingly, plants lacking all three GALS genes did not exhibit any obvious developmental problems under standard growth conditions. This suggests that other enzymes may be involved in initiating galactan synthesis or that the absence of galactans can be compensated for by other cell wall components. However, further analysis revealed that the RG-I in these triple mutants retained branching, indicating that the initial galactose substitutions on the RG-I backbone are added by enzymes different from GALS.

The Future of Galactan Synthase Research

This research provides a significant step forward in understanding the complex process of pectin biosynthesis. By identifying and characterizing the function of all three GALS enzymes in Arabidopsis, scientists have gained valuable insights into the construction of plant cell walls.

The findings have implications for various applications, including:

<ul> <li>Biofuel Production: Engineering plants with modified galactan content could improve the efficiency of converting plant biomass into biofuels.</li> <li>Plant Resilience: Understanding how galactans contribute to cell wall structure and function could lead to strategies for enhancing plant resistance to stress and disease.</li> <li>Food Science: Modifying pectin structure could alter the texture and properties of plant-based foods.</li> </ul>

About this Article -

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This article is based on research published under:

DOI-LINK: 10.1093/pcp/pcy180, Alternate LINK

Title: The Three Members Of The Arabidopsis Glycosyltransferase Family 92 Are Functional Β-1,4-Galactan Synthases

Subject: Cell Biology

Journal: Plant and Cell Physiology

Publisher: Oxford University Press (OUP)

Authors: Berit Ebert, Devon Birdseye, April J M Liwanag, Tomas Laursen, Emilie A Rennie, Xiaoyuan Guo, Michela Catena, Carsten Rautengarten, Solomon H Stonebloom, Pawel Gluza, Venkataramana R Pidatala, Mathias C F Andersen, Roshan Cheetamun, Jenny C Mortimer, Joshua L Heazlewood, Antony Bacic, Mads H Clausen, William G T Willats, Henrik V Scheller

Published: 2018-09-01

Everything You Need To Know

What are galactan synthases, and what is their role?

Galactan synthases are enzymes that add galactose sugars to a growing polysaccharide chain. Specifically, they create β-1,4-galactans, which are side chains in rhamnogalacturonan-I (RG-I), a major component of pectin within the plant cell walls. The identification of GALS1, GALS2, and GALS3 as galactan synthases provides valuable insights into the process of plant cell wall construction.

Why is pectin important, and how does the research on galactan synthases relate to it?

Pectin is crucial for plant growth, development, and defense, as it is a major component of plant cell walls. Understanding the biosynthesis of pectin is essential for improving plant health and utilizing plants for various applications, such as biofuel production and creating more robust plant-based resources. The study of galactan synthases contributes to this understanding by revealing how galactose sugars are added to the pectin molecule, thereby influencing its structure and function.

What is the significance of identifying GALS1, GALS2, and GALS3?

The significance of the study lies in identifying all three members of the Arabidopsis GT92 family, specifically GALS1, GALS2, and GALS3, as functional β-1,4-galactan synthases. This means that these enzymes are responsible for adding galactose sugars to the pectin molecule, contributing to plant cell wall construction. This is a major step forward in understanding pectin biosynthesis and opens doors for engineering plants with improved characteristics.

What are the potential implications of this research on galactan synthases?

The implications of this research are far-reaching. By understanding the role of galactan synthases, scientists can potentially manipulate the composition of plant cell walls. This could lead to the development of plants with enhanced properties, such as increased strength, improved resistance to stress, or more efficient conversion into biofuels. The ability to control pectin biosynthesis could revolutionize various aspects of plant-based resources.

What did the study reveal about the function and location of the GALS enzymes?

The study found that GALS1, GALS2, and GALS3 are localized to the Golgi apparatus, which is consistent with their role in pectin biosynthesis. These enzymes function by adding galactose sugars to existing galactose residues on the RG-I backbone. While the absence of all three GALS genes did not cause any observable developmental problems under standard growth conditions, the RG-I in these triple mutants retained branching, implying other enzymes might be involved in the initial galactose substitutions on the RG-I backbone.