International Journal of Biological Macromolecules 27 (2000) 139–144 New perspectives on the endo-beta-glucanases of glycosyl hydrolase Family 17  Bruce R. Thomas a, *, Gabriel O. Romero b , Donald J. Nevins c , Raymond L. Rodriguez a a Section of Molecular and Cellular Biology, Uniersity of California, Dais, CA 95616 -8535, USA b Philippine Rice Research Institute, Munoz, Nuea Ecija, Philippines c Department of Vegetable Crops, Uniersity of California, Dais, CA 95616 -8631, USA Accepted 5 January 2000 Abstract Isozymes of glycosyl hydrolase Family 17 hydrolyze 1,3--glucan polysaccharides found in the cell wall matrix of plants and fungi, enabling these plant enzymes to serve diverse roles in plant defense and plant development. Fourteen genes from Family 17 have been characterized in the genome of rice. A sequence dendrogram analysis divided these genes into four subfamilies. The recombinant GNS1 enzyme from subfamily B had 1,3;1,4--glucanase activity, suggesting a role for this isozyme in plant development. © 2000 Elsevier Science B.V. All rights reserved. Keywords: -Glucanase; Rice (Oryza satia L.); Gene dendrogram; Heterologous expression www.elsevier.com/locate/ijbiomac 1. Introduction Plant-encoded isozymes of glycosyl hydrolase Family 17 hydrolyze 1,3--glucan polysaccharides found in the cell wall matrix of plants and fungi [1]. These isozymes include the endo-1,3--glucanases (E.C. 3.2.1.39, Sub- family A), the endo-1,3;1,4--glucanases (E.C. 3.2.1.73, Subfamily B) and subfamilies C and D whose enzy- matic specificity is unknown [2–4]. 1,3--Glucan and related polysaccharides are found in many specialized stages of plant development including cell division [5], microsporogenesis [6], pollen tubes [7], hypocotyls [8], cotton fibers [9], developing endosperm [10], seed ger- mination [11], wound healing [12] and dormancy [13]. Members of the grass family produce 1,3;1,4--glucan polymers in the cell wall matrix of endosperm and a wide range of growing tissues [14]. Breakdown of this polymer may provide substantial nutrition for germina- tion and seedling development and facilitate the access of other hydrolases to their substrates in the endosperm [15]. Plants also encounter a wide range of 1,3-- and 1,3;1,6--glucan polymers in the cell walls of fungi [16,17] that attempt to invade the plant. Some plant glucanase enzymes appear to have evolved into a de- fense role, preferentially attacking the fungal cell walls and releasing glucan oligosaccharides. Certain of these oligosaccharides can act as elicitors, signaling to the plant that an infection is occurring and stimulating the expression of a range of defense genes within the plant. Thus, the plant enzymes that produce and break down these -glucan polymers have diverse roles in plant defense [18 – 21] and plant development [14,22]. Among the glucan hydrolases that have evolved to serve these diverse roles are the endoglucanases en- coded by glycosyl hydrolase gene Family 17 [23], with fourteen genes characterized in the genome of rice. These rice glucanase genes have diverse patterns of expression in various tissues and in response to various treatments [3]. Distinct substrate preferences of glu- canase isozymes have been documented in a number of studies [24 – 26]. Subtle differences in substrate specific- ity for hydrolysis near branch points may distinguish glucanase isozymes that produce elicitors [20] versus  This manuscript is based on a presentation at the 1998 Plant Polysaccharide Symposium, Davis, California, USA * Corresponding author. Tel.: +1-530-7520269; fax: +1-530- 7521185. E-mail address: brthomas@ucdavis.edu (B.R. Thomas) 0141-8130/99/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0141-8130(00)00109-4