Abstract text: Arabinogalactan proteins (AGP) are linked to various physiological processes, but their specific role in cell wall dynamics, particularly during significant remodelling events, is not well understood. AGPs are heavily glycosylated proteins with type II arabinogalactan (AGII) playing a crucial role in their function. AGII comprises a central core of β-(1,3)-galactan with branches of β-(1,6)-galactan further substituted with arabinose and other minor sugars.

In this study we investigate the function of AGII in the structural organization of the cell wall during the cessation of elongation and the transition to secondary growth. We analysed basal stem internodes of Arabidopsis thaliana plants overproducing a chickpea Beta-Galactosidase (35S::βV-Gal plants) that specifically hydrolyses the β-(1,3) and β-(1,6) galactosyl residues of AGII. We confirmed that the enzyme accumulated in basal internodes and acted in AGII chains in muro. These plants showed a 5% reduction in basal internode diameter and changes in pectin, hemicellulose, and lignin composition. Specifically, there was an increase in homogalacturonan methyl-esterification, alterations in xylan distribution within the cellulose network, increased lignin deposition, and enhanced cell wall resistance to enzymatic degradation.

These findings highlight the contribution of AGPs to the structure of the cell wall and their role in shaping the secondary cell walls.