Abstract
Penium margaritaceum is a new and valuable unicellular model organism for studying plant cell wall structure and developmental dynamics. This charophyte has a cell wall composition remarkably similar to the primary cell wall of many higher plants and clearly-defined inclusive zones containing specific polymers. Penium has a simple cylindrical phenotype with a distinct region of focused wall synthesis. Specific polymers, particularly pectins, can be identified using monoclonal antibodies raised against polymers of higher plant cell walls. Immunofluorescence-based labeling is easily performed using live cells that subsequently can be returned to culture and monitored. This feature allows for rapid assessment of wall expansion rates and identification of multiple polymer types in the wall microarchitecture during the cell cycle. Cryofixation by means of spray freezing provides excellent transmission electron microscopy imaging of the cell, including its elaborate endomembrane and cytoskeletal systems, both integral to cell wall development. Penium’s fast growth rate allows for convenient microarray screening of various agents that alter wall biosynthesis and metabolism. Finally, recent successful development of transformed cell lines has allowed for non-invasive imaging of proteins in cells and for RNAi reverse genetics that can be used for cell wall biosynthesis studies.
Highlights
The Penium cell wall consists of two dominant components, a homogalacturonan (HG)-rich outer layer that is complexed with calcium (Ca2+) and that is manifested by the lattice that is positioned on the cell wall surface [26]
These protocols have been especially valuable in studies of wall development in cells treated with cytoskeletal poisons, various cations, enzymes and exogenous pectins [26,38,39]
Penium contains an elaborate endomembrane system consisting of 100–125 Golgi bodies per cell, numerous vesicle types involved in secretory activities and a highly dynamic cytoplasmic streaming network that transports the vesicles
Summary
The utilization of new research methods and strategies emerging from technologies in molecular genetics, immuno-binding/cytochemical labeling, high resolution microscopy and spectroscopy have recently provided significant insight into deciphering the complexities of the plant cell wall [1,2,3,4,5,6]. Biochemical and immunobinding-based screening (including, comprehensive polymer profiling, CoMPP, and immunocytochemistry) has revealed that the charophytes have cell wall polymer composition profiles that are remarkably similar to those of land plants [19,20,21] This includes a cellulose microfibril infrastructure with associated hemicelluloses (mannans, xylans, xyloglucans) embedded in a pectin matrix. My laboratory isolated a clone of the charophyte, Penium margaritaceum, and it has become increasingly valuable in cell wall studies This alga is unicellular, produces only a primary cell wall that has clearly defined domains of cellulose, pectin and other wall polymers and can be manipulated for both microscopy-based analyses and experimental screening [25,26]. The attributes of, and protocols for, using Penium in multiple areas of cell wall research are presented
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