IDENTIFICATION AND MAP LOCATION OF TTR1, A SINGLE-LOCUS IN ARABIDOPSIS-THALIANA THAT CONFERS TOLERANCE TO TOBACCO RINGSPOT NEPOVIRUS

The interaction between Arabidopsis and the nepovirus tobacco ringspot virus (TRSV) was characterized. Of 97 Arabidopsis lines tested, all w ere susceptible when inoculated with TRSV grape strain. Even though th ere was systemic spread of the virus, there was a large degree of vari ation in symptoms as the most sensitive lines died 10 days after inocu lation, while the most tolerant lines either were symptomless or devel oped only mild symptoms. Four lines were selected for further study ba sed on their differential reactions to TRSV. Infected plants of line C ol-0 and Col-0 gl1 flowered and produced seeds like noninfected plants , while those of lines Estland and 1155 died before producing seeds, S ymptoms appeared on sensitive plants approximately 5 to 6 days after i noculation. Serological studies indicated that in mechanically inocula ted seedlings, the virus, as measured by coat protein accumulation, de veloped at essentially the same rates and to the same levels in each o f the four lines, demonstrating that differences in symptom developmen t were not due to a suppression of virus accumulation, Two additional TRSV strains gave similar results when inoculated on the four lines. G enetic studies with these four Arabidopsis lines revealed segregation of a single incompletely dominant locus controlling tolerance to TRSV grape strain, We have designated this locus TTR1. By using SSLP and CA PS markers, TTR1 was mapped to chromosome V near the nga129 marker, Se ed transmission frequency of TRSV for Col-0 and Col-0 gl1 was over 95% and their progeny from crosses all had seed transmission frequencies of over 83%, which made it possible to evaluate the segregation of TTR I in F-2 progeny from infected F-1 plants without inoculating F-2 plan ts, Seed transmission of TRSV will be further exploited to streamline selection of individuals for fine mapping the TTRI gene. The identific ation of tolerant and sensitive interactions between TRSV and A. thali ana lines provides a model system for genetic and molecular analysis o f plant tolerance to virus infection.