Fine genetic mapping of the <Emphasis Type="Italic">TuNI</Emphasis> locus causing systemic veinal necrosis by turnip mosaic virus infection in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

In the pathosystem of turnip mosaic virus (TuMV) and Arabidopsis thaliana, two distinct symptoms (mosaic symptom and veinal necrosis) were observed that were dependent upon the combination of the TuMV isolate and the Arabidopsis ecotype. The Col-0 ecotype developed mosaic symptoms after infection with the TuMV isolate Azu while the Ler ecotype developed veinal necrosis after infection with the same TuMV isolate. The Ler phenotype is controlled by a single dominant gene TuNI (TuMV necrosis inducer) which is located on chromosome 1. The TuNI gene was precisely mapped to the ~105 kb interval between the two markers of mXF41 and mRF28 by using several types of DNA polymorphism markers. Within this region, which included largely duplicated sequences, a total of 19 putative genes were predicted and 15 of these were classified into five gene families. The genes belonging to the gene families At1g58480 and At1g58602 may function in response to infection by pathogens. The gene family At1g58480 encodes lipase-like proteins, which might be involved in the induction of defence responses that are mediated by salicylic acid. The gene family At1g58602 encodes the CC-NBS-LRR (CNL) proteins, which are known to function as one of the plant resistance (R) proteins against pathogens. In the present study, the possibility that TuNI might function as an R gene was discussed.Y.K. and T.I. contributed equally to this study