Screening for genetic elements involved in the nonhost response of sugar beet [Beta vulgaris] to the plasmodiophorid cereal root parasite Polymyxa graminis by representational difference analysis

Representational difference analysis (RDA) was used to select and clone cDNA fragments of genes whose steady state transcription was upregulated in sugar beet challenged with the nonhost parasite Polymyxa graminis. In silico analysis revealed that sequences with similarities to plant defence genes as well as genes of unknown function were represented amongst the cloned cDNAs. The utility of RDA was verified when, in material from the nonhost interaction, semiquantitative RT-PCR confirmed transcriptional upregulation of at least 10 of 17 genes randomly selected from the RDA library. Time-course transcriptional analysis of two plant defence gene-like sequences demonstrated that, in sugar beet, both were upregulated within 1 h in response to P. graminis but not to P. betae. This work comprises the first report of an active response by sugar beet to P. graminis.