Exploring the Role of β-1,3-Glucanase in Aerenchyma Development in Sugarcane Roots.

Background and aims: Aerenchyma formation has emerged as a promising model for understanding cell wall modifications. Certain cells undergo programmed cell death (PCD), while others do not, suggesting the existence of a tightly regulated signaling dispersion mechanism. Cell-to-cell communication occurs via plasmodesmata, whose permeability is regulated by the deposition of callose (β-1,3-glucan) and its degradation by β-1,3-glucanase. These processes may be key to understanding the selection of specific cells, which modify their cell walls for aerenchyma formation. Therefore, this study aims to characterize the role of callose and β-1,3-glucanase during aerenchyma formation.

Methods: Sugarcane roots were segmented into five 1cm sections and embedded in LR-White resin. Semi-thin sections were obtained, and immunolocalization was performed using monoclonal antibodies for the polysaccharides callose (β-1,3-glucan) and mixed-linkage β-1,3-1,4-glucan. The protein for in situ localization was chosen based on its ontology and protein domain structure. A super-resolution microscope was utilized to identify the antibody signal deposition pattern.

Key results: The antibody signal against mixed-linkage β-1,3-1,4-glucan was continuously detected along the cell wall in the early root segments. Its removal and degradation became evident from the third segment onward, coinciding with aerenchyma formation. In contrast, callose exhibited a punctate signal, possibly marking regions of plasmodesmata. Callose degradation followed a similar pattern to that of mixed-linkage β-1,3-1,4-glucan (S3-S5), though its signal was less abundant. The β-1,3-glucanase showed peak signal from segment 3 to segment 4, accompanied by a punctate signal, suggesting its action at regions of plasmodesmata and callose degradation sites.

Conclusion: The presence of callose raises critical questions about how cells transmit signals and why only certain cells undergo PCD. Managing the permeability and selectivity of intercellular communication may be a key factor in various biological processes. Gaining insight into these mechanisms and identifying potential enzymes and polysaccharides could provide new perspectives for future research.