Xyloglucan remodelling in cell wall plays a critical role in controlling seed germination

Seeds are essential to agriculture and biodiversity; most food for both humans and animals is derived from them. Germination efficiency is a key factor in crop yield.

Germination involves mechanisms of cell wall remodelling that regulate both embryo growth and mechanical resistance of surrounding tissues. Plant cell wall remodelling facilitates the emergence of the radicle through protective tissues during germination and remains an essential process for subsequent plant growth. Understanding the physicochemical properties of the cell wall, the genes involved, and their regulation is of major interest for improving seed germination, plant growth, and architecture. Xyloglucans are major components of plant cell walls. These polysaccharides are composed of glucose chains bearing side branches of xylose, galactose, and fucose. Within the wall, enzymes modify chain length and sugar composition. However, their role in the fine regulation of wall elasticity remains to be fully elucidated. A mutant of Arabidopsis thaliana affected in seed dormancy* was found to be impaired in xyloglucan remodelling. This mutant has enabled broader investigation into the role of xyloglucan remodelling in seed physiology.

Analysis of a range of mutants affected in enzymes involved in xyloglucan biosynthesis or remodelling showed that reduced dormancy was strictly correlated with the absence of xylose cleavage. The xylosidase XYL1 is an apoplastic* enzyme that cleaves xylose residues attached to the glucose backbone of xyloglucans; its inactivation results in a loss of seed dormancy. A polarised accumulation of xyloglucans in elongating tissues was observed during germination. Loss of XYL1 function prevents this polarisation and also leads to the accumulation of oxidised oligosaccharides, defects not observed in other glycosidase mutants. The absence of xylose cleavage is thought to cause excessive release of free oligosaccharides, which may alter intracellular trafficking of xyloglucans. Their oxidation may lead to their inactivation, thereby limiting potential deleterious effects.

The acquisition of new knowledge on the fine regulation of the composition and remobilisation of the various cell wall polymers is of great interest for controlling germination and, more broadly, plant development and growth. The mechanisms underlying the release and inactivation of free oligosaccharides, and their potential roles as signalling molecules in cell wall remodelling, remain important areas for further research.
The identification of the function of the xylosidase XYL1 and of xyloglucan-derived oligosaccharides in Arabidopsis seeds potentially opens the way to the development of tools for targeted engineering of seed germination in crop species, to better meet agricultural and industrial needs.

* Dormancy is a resting state in which the seed does not germinate. It is considered an ecological survival adaptation that allows the seed to wait until conditions are favourable for germination.
The apoplast is the network of cell walls, intercellular spaces and structures such as xylem vessels in plants.


Research developed at the Institute Jean-Pierre Bourgin for Plant Sciences in collaboration.