Defence Gene Expression and DNA Structure Mutation in Tobacco Resistant to Brown Spot

AT-toxin produced by a virulent strain TBA28 of tobacco brown spot pathogen Alternaria alternata induced systemic resistance being over 80& of a susceptible cultivar NC89. The resistance induced by the toxin was 20% higher than that by a hypovirulent strain TBA 16 of the pathogen. A resistant somaclone NC89-TT had been produced by the process of tissue culture and plant regeneration, in which AT-toxin was used as pressuring factor. NC89-TT was reproduced by seed production. 

Expressions of 5 defence genes were tested and DNA structural alternations were analyzed. Dot blots of RNAs from NC89 and NC89-TT plants either immunized by the elicitor and AT-toxin or untreated were probed with cDNAs for pathogensis-related (PR) protein PR-la, chitinase (CHT), phenylalanine ammonia lyase (PAL), chalcone synthase (CHS), and lipoxygenase (LOX). Both PAL and PR-la genes did not constitutively transcript in untreated NC89, and did in the fourth generation plants of NC89-TT. While, CHT gene was inverse. 

Transcription of PR-la gene was activated by elicitor or AT-toxin. A consistent tendency was found between the transcription activity in NC89 plants induced by PR-LA electrophoresis. Genome DNA structure mutation in different tobaccos was tested by random amplified polymorphric DNA (RAPD) using 5 primers. 

It was suggested that the sequence rearrangement or nucleotide substitution was responsible for the constitutive expression of the defence genes and such an expression resulted in resistance enhancement.

Tobacco brown spot induced resistance resistant somaclone NC89-TT defence genes
Gene mutation

SOURCE FROM Chinese Tobacco Science