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First published online December 11, 2003; 10.1104/pp.103.030072 Plant Physiology 134:339-351 (2004) © 2004 American Society of Plant Biologists Occurrence of the Primary Cell Wall Polysaccharide Rhamnogalacturonan II in Pteridophytes, Lycophytes, and Bryophytes. Implications for the Evolution of Vascular Plants1National Agricultural Research Center for Kyushu Okinawa Region, Nishigoshi, Kumamoto 861-1192, Japan (T.M.); Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan (T.I.); National Science Museum, Tsukuba, Ibaraki 305-0005, Japan (S.M., M.H.); and Complex Carbohydrate Research Center, The University of Georgia, 315 Riverbend Road, Athens, Georgia 30602 (A.D., P.A., M.A.O.)
Borate ester cross-linking of the cell wall pectic polysaccharide rhamnogalacturonan II (RG-II) is required for the growth and development of angiosperms and gymnosperms. Here, we report that the amounts of borate cross-linked RG-II present in the sporophyte primary walls of members of the most primitive extant vascular plant groups (Lycopsida, Filicopsida, Equisetopsida, and Psilopsida) are comparable with the amounts of RG-II in the primary walls of angiosperms. By contrast, the gametophyte generation of members of the avascular bryophytes (Bryopsida, Hepaticopsida, and Anthocerotopsida) have primary walls that contain small amounts (approximately 1% of the amounts of RG-II present in angiosperm walls) of an RG-II-like polysaccharide. The glycosyl sequence of RG-II is conserved in vascular plants, but these RG-IIs are not identical because the non-reducing L-rhamnosyl residue present on the aceric acid-containing side chain of RG-II of all previously studied plants is replaced by a 3-O-methyl rhamnosyl residue in the RG-IIs isolated from Lycopodium tristachyum, Ceratopteris thalictroides, Platycerium bifurcatum, and Psilotum nudum. Our data indicate that the amount of RG-II incorporated into the walls of plants increased during the evolution of vascular plants from their bryophyte-like ancestors. Thus, the acquisition of a boron-dependent growth habit may be correlated with the ability of vascular plants to maintain upright growth and to form lignified secondary walls. The conserved structures of pteridophyte, lycophyte, and angiosperm RG-IIs suggests that the genes and proteins responsible for the biosynthesis of this polysaccharide appeared early in land plant evolution and that RG-II has a fundamental role in wall structure.
1 This work was supported in part by the U.S. Department of Energy (grant nos. DE-FG02-96-ER20220 to A.D. and DE-FG05-93-ER20097 to A.D. and P.A.) and by the Bio-oriented Technology Research Advancement Institution (grants to T.I.). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.103.030072. * Corresponding author; e-mail mao{at}ccrc.uga.edu; fax 706-542-4412. Received July 10, 2003; returned for revision August 21, 2003; accepted September 14, 2003. Related articles in Plant Physiol.:
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