Deep structural analysis of rhamnogalacturonan-I (RG-I) in Arabidopsis reveals new insights into pectin diversity

Pectic polysaccharides are an integral part of primary plant cell walls, where they are perfrom crucial structural and biological functions. Pectin is generally divided into four distinct structural categories, including homogalacturonan, xylogalacturonan, rhamnogalacturonan I (RG-I) and rhamnogalacturonan II. Among the four main pectin domains, the structural intricacies of rhamnogalacturonan-I (RG-I) remain the least understood, especially in widely employed plant models. We employed multiple complementary analytical techniques to present a detailed structural analysis of RG-I in the model system Arabidopsis thaliana. Using highly purified RG-I from different tissues, we conducted comparative linkage and NMR analyses, complemented by mass spectrometry of enzymatically digested RG-I oligosaccharides. Our findings present the most comprehensive structural overview of Arabidopsis RG-I to date, revealing novel structural features. Notably, we identified O -acetylation of rhamnose backbone residues as a predominant feature, a modification previously unreported in this species. The combined results present a comprehensive structural overview of Arabidopsis thaliana RG-I that will serve as a roadmap for studying pectin biosynthesis and function.