Infection with the Obligate Biotroph Plasmodiophora braßicae, the Causal Agent of the Club Root Disease, does not Affect Expreßion of NIT-1/2-related Nitrilases in Roots of Chinese Cabbage

Abstract

Summary The infection of Chinese cabbage ( Brasica rapa sp. pekinensis cv. Granaat) with the causal agent of the club root disease, Plasmodiophora brasicae Wor., leads to tumorous swellings of the root as a result of increased cell division and hypertrophy. An increased auxin formation in infected tisue 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 Lstrand cDNA, synthesized from hypocotyl total RNA, by polymerase chain reaction. Also, genomic nitrilase fragments from Chinese cabbage and Brasica oleracea, another host for P. brasicae , 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 by of coding region) as a probe, nitrilase mRNA was determined in total RNA from P. brasicae -infected and healthy root tisue of Chinese cabbage. In both tisues a mRNA of approx. 1.3 kB was detected with similar amounts in infected and healthy tisues. Our results suggest that the biotrophic pathogen P. brasicae does not affect expresion of NIT 1/2-related nitrilase(s) at the transcriptional level.