Probing homogalacturonan in situ: A comprehensive review of available molecular recognition tools.

Among the major plant cell wall components, pectic-type homogalacturonan emerges as a chemically and spatiotemporally dynamic matrix-forming agent embedded within the cell wall through various inter- and intramolecular interactions. Its abundance, localization, and chemistry profoundly influence cell wall biomechanics and all facets of plant physiology. Precise tracking of homogalacturonan in a native context is crucial for understanding cell wall organization, particularly the relation between molecular structure and function. It also enables the detailed characterization of plant-based resources for industrial, food, and biomedical applications. This review offers a comprehensive and focused survey of the state-of-the-art molecular recognition tools being employed to visualize homogalacturonan in diverse plant samples. We particularly highlight homogalacturonan-specific monoclonal antibodies, which represent the most used and well-established probes. However, we also discuss less common reagents, such as fluorophores, oligosaccharide-based probes, carbohydrate-binding modules, and whole enzymes, as well as emerging chemical biology approaches exemplified by click chemistry. We critically evaluate their strengths, limitations, and suitability for given research objectives and provide the most notable examples of their usage. Lastly, we outline the anticipated future expansion of an advanced, improved range of new molecular tools, which holds the potential to overcome some of the current experimental hurdles.