Infection with the obligate biotroph Plasmodiophora brassicae, the causal agent of the club root disease, does not affect expression of NIT1 2-related nitrilases in roots of Chinese cabbage

The infection of Chinese cabbage (Brassica rapa ssp. pekinensis cv. Granaat) with the causal agent of the club root disease, Plasmodiophora brassicae Wor., leads to tumorous swellings of the root as a result of increased cell division and hypertrophy. An increased auxin formation in infected tissue by enzymatic hydrolysis of the precursor indole-3-acetonitrile has previously been postulated. Based on a recently published nitrilase cDNA sequence of Arabidopsis thaliana, we have amplified a partial nitrilase cDNA fragment from Chinese cabbage 1.strand cDNA, synthesized from hypocotyl total RNA, by polymerase chain reaction. Also, genomic nitrilase fragments from Chinese cabbage and Brassica oleracea, another host for P. brassicae, were amplified with the same set of primers. Sequence comparisons indicate high homology in exon and intron regions. The sequenced isoform of Chinese cabbage is most closely related to the NIT isoforms 1 and 2 of A. thaliana. Using the homologous nitrilase cDNA fragment (504 bp of coding region) as a probe, nitrilase mRNA was determined in total RNA from P. brassicae-infected and healthy root tissue of Chinese cabbage. In both tissues a mRNA of approx. 1.3 kB was detected with similar amounts in infected and healthy tissues. Our results suggest that the biotrophic pathogen P. brassicae does not affect expression of NIT 1/2-related nitrilase(s) at the transcriptional level.