Pectin Structural Dynamics: Developmental and Evolutionary Perspectives.

Plant cell walls play a crucial role in plant development and evolution. This structure is primarily composed of proteins and polysaccharides, including cellulose, hemicellulose, and pectins. Homogalacturonan (HG), the most abundant pectin in the primary cell wall, is synthesized by α -1,4-D-GALACTURONOSYLTRANSFERASE (GAUT) enzymes, methylesterified, and subsequently secreted into the apoplast. The dynamics of pectin methylesterification is regulated by enzymes such as PECTIN METHYLESTERASES (PMEs) and PECTIN METHYLESTERASE INHIBITORS (PMEIs). Across plant evolution and development, different cell types display distinct domains of pectin methylesterification. The binding of de-methylesterified pectins to the Catharanthus roseus RECEPTOR-LIKE KINASE 1-LIKE (CrRLK1L) proteins and RAPID ALKALINIZATION FACTOR (RALF) peptides is involved in pectin signaling and cell wall integrity maintenance during developmental processes. While phylogenetic studies highlight molecular innovations in pectin metabolism, functional studies remain scarce outside of angiosperms. Furthermore, the explicit role of de-methylesterified pectin in coupling cell wall structure to intracellular signaling has only been demonstrated in angiosperms. Comparative functional studies addressing key evolutionary transitions will ultimately reveal how pectin metabolism has contributed to morphological innovations across plant evolution.