The trans-Golgi sorting and the exocytosis of xylogalacturonan from the root border/border-like cell are conserved among monocot and dicot plant species

Abstract

Root border cells lie at the interface between the root cap and the soil, secreting mucilage containing polysaccharides and molecules influencing microbial growth around the root. Border cells are sloughed off from the root surface, and the detachment is associated with secretion of xylogalacturonan (XGA). Recently, we showed that in alfalfa XGA secretion is mediated by large vesicles arising from the trans-Golgi in root cap cells. These vesicles are detected in precursor cells of border cells, but their fusion with the plasma membrane is observed only in border cells. We have now examined XGA secretion from maize border cells and Arabidopsis border-like cells using transmission electron microscopy and immunolabeling. In the root caps of both species, XGA is packaged into vesicles derived from the trans-Golgi, not in the vesicles from the trans-Golgi network as in the alfalfa root cap. Border cell-specific exocytosis of XGA was observed in the maize root suggesting that sorting and secretion of XGA in the root cap are conserved in monocot plants.

Root extracellular traps versus neutrophil extracellular traps in host defence, a case of functional convergence?

“…These are synthesized and transported via the secretory pathway involving the ER, Golgi stacks and Golgi‐derived secretory vesicles (Driouich et al , , ). Electron microscopy imaging revealed the presence of a large number of Golgi stacks and secretory dense vesicles in AC‐DCs of Arabidopsis thaliana , pea, flax (Vicré et al , ; Cannesan et al , ; Driouich et al , ; Plancot et al , ) and recently in alfalfa Medicago sativa (Wang et al , ; Wang & Kang, ). Secretion of Golgi‐derived molecules by AC‐DCs into the extracellular space persists even after cell detachment from the root cap.…”

Mucilage extracted from Chilean papaya seeds is enriched with homogalacturonan domains

“…Notably, in Arabidopsis, xylogalacturonan is present in the root cap mucilage, co-secreted with HG in detached cells from these structures, which serve to shield the roots from soil friction. Recently, there has been a suggestion that XGA could play a role in root defense against pathogens ( Durand et al., 2009 ; Wang and Kang, 2018 ). Investigating this potential could open promising avenues for future research.…”