Trimming galactose side chains of arabinogalactan proteins alters pectin and hemicellulose deposition in secondary cell walls of Arabidopsis thaliana floral stem internodes.

Abstract

Shaping the cell wall composition and structure to meet the requirements of different tissues and developmental stages relies on multiple actors, including arabinogalactan proteins (AGPs). Although the specific role of these proteins in cell wall dynamics is still under debate, especially in events involving significant remodeling of the cell wall, their carbohydrate motif, type II arabinogalactan (AGII), seems to be crucial for their function. This study aims to investigate the function of AGII, specifically the galactose residues of its side chains, in the structural organization of the cell wall during the cessation of elongation and the transition to secondary growth. To achieve this, we characterized floral stem internodes of Arabidopsis thaliana plants overproducing the chickpea βV-galactosidase protein (35S::βV-Gal plants), an enzyme that specifically hydrolyzes the β-(1,3)- and β-(1,6)-galactosyl residues of AGII. Changes induced in the cell wall by trimming galactose residues of AGII resulted in a noticeable increase in homogalacturonan methyl esterification. Additionally, these neutral galactose side chains may regulate hemicellulose-cellulose interactions and influence xylan distribution through the cellulose network, which in turn affects the deposition of lignin and determines its recalcitrance to enzymatic degradation.