ISSN:
1573-5028
Keywords:
glucanase
;
cDNA cloning
;
Nicotiana tabacum
;
pathogenesis-related proteins
;
plant defense genes
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Glucan endo-1,3-β-glucosidases (β-1,3-glucanases) have been implicated in several developmental processes and they may also play a direct role in the plant's defense against fungal pathogens. In an effort to characterize the glucanase gene family, complementary DNA clones encoding an acidic form of β-1,3-glucanase have been isolated from tobacco. The cDNA was expressed in E. coli and shown to encode a β-1,3-glucanase activity. The protein sequence encoded by the cDNA was found to match the partial protein sequence of PR-35, a previously characterized β-1,3-glucanase [29]. The protein encoded by the cDNA was purified from the extracellular fluid of TMV-infected tobacco leaves and found by immunological methods to correspond to glucanase PR-Q' [10]. From a detailed analysis of the cDNA it is clear that this glucanase represents a third structural class of enzyme which differs substantially from both the basic, vacuolar glucanase and the acidic, extracellular forms (PR-2, PR-N and PR-O). It has previously been demonstrated that the basic form of β-1,3-glucanase is synthesized as a pre-pro-enzyme and upon maturation the 21 amino acid signal peptide and a 22 amino acid carboxy-terminal peptide are removed. This processing event has been proposed to be involved with the vacuolar localization of the enzyme. By comparing the deduced protein structure of PR-Q' to that of the basic form it is evident that this extracellular enzyme is missing the carboxy-terminal 22 amino acids. The role of a conserved phenylalanine-glycine dipeptide in the processing of glucanases and other pathogenesis-related proteins from tobacco is discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00039420
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