Fungal pathogens secrete an inhibitor protein that distinguishes isoforms of plant pathogenesis-related endo-beta-1,3-glucanases

被引:49
作者
Ham, KS
Wu, SC
Darvill, AG
Albersheim, P
机构
[1] UNIV GEORGIA,COMPLEX CARBOHYDRATE RES CTR,ATHENS,GA 30602
[2] UNIV GEORGIA,DEPT BIOCHEM & MOL BIOL,ATHENS,GA 30602
关键词
D O I
10.1046/j.1365-313X.1997.11020169.x
中图分类号
Q94 [植物学];
学科分类号
071001 ;
摘要
Plant endo-beta-1,3-glucanases and chitinases inhibit the growth of some fungi and generate elicitor-active oligosaccharides while depolymerizing polysaccharides of mycelial walls. Overexpression of the endo-beta-1,3-glucanases and/or chitinases in transgenic plants provides, in some cases, increased protection against fungal pathogens. However, most of the phytopathogenic fungi that have been tested in vitro are resistant to endo-beta-1,3-glucanases and chitinases. Furthermore, some phytopathogenic fungi whose growth is inhibited by these enzymes are able to overcome the effect of these enzymes over a period of hours, indicating an ability of those fungi to adapt to the enzymes. Evidence is presented indicating that fungal pathogens secrete proteins that inhibit selective plant endo-beta-1,3-glucanases. A glucanase inhibitor protein (GIP-1) has been purified to homogeneity from the culture fluid of the fungal pathogen of soybeans, Phytophthora sojae f. sp. glycines (Psg), and two basic pathogenesis-related endo-beta-1,3-glucanases (EnGL(soy)-A and EnGL(soy)-B) have been purified from soybean seedlings. GIP-1 inhibits EnGL(soy)-A but not EnGL(soy)-B. Moreover, GIP-1 does not inhibit endo-beta-1,3-glucanases secreted by Psg itself nor does GIP-1 inhibit PR-2c, a pathogenesis-related endo-beta-1,3-glucanase of tobacco. Evidence is presented that Psg secretes other GIPs that inhibit other endo-beta-1,3-glucanase(s) of soybean. Furthermore, GIP-1 does not exhibit proteolytic activity but does appear to physically bind to EnGL(soy)-A. The results reported herein demonstrate specific interactions between gene products of the host and pathogen and establish the need to consider fungal proteins that inhibit plant endo-beta-1,3-glucanases when attempting to use the genes encoding endo-beta-1,3-glucanases to engineer resistance to fungi in transgenic plants.
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页码:169 / 179
页数:11
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