SummaryThe dominant locus, RCY1, in the Arabidopsis thaliana ecotype C24 confers resistance to the yellow strain of cucumber mosaic virus (CMV-Y). The RCY1 locus was mapped to a 150-kb region on chromosome 5. Sequence comparison of this region from C24 and a CMV-Y-susceptible C24 mutant predicts that the RCY1 gene encodes a 104-kDa CC-NBS-LRR-type protein. The RCY1 gene from C24, when expressed in the susceptible ecotype Wassilewskija (Ws), restricted the systemic spread of virus. RCY1 is allelic to the resistance genes RPP8 from the ecotype Landsberg erecta and HRT from the ecotype Dijon-17, which confer resistance to Peronospora parasitica biotype Emco5 and turnip crinkle virus (TCV), respectively. Examination of RCY1 plants defective in salicylic acid (SA), jasmonic acid (JA) and ethylene signaling revealed a requirement for SA and ethylene signaling in mounting a resistance response to CMV-Y. The RCY1 nahG etr1 double mutants exhibited an intermediate level of susceptibility to CMV-Y, compared to the resistant ecotype C24 and the susceptible ecotypes Columbia and Nossen. This suggests that in addition to SA and ethylene, a novel signaling mechanism is associated with the induction of resistance in CMV-Y-infected C24 plants. Moreover, our results suggest that the signaling pathways downstream of the RPP8, HRT, and RCY1 have evolved independently.

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999 The entire 3.7 kbp 5´-upstream region (–2840 to +886) from the translational start codon of NADH–glutamate synthase (NADH–GOGAT, EC 1.4.1.14) gene from rice (Oryza sativa L.) or the region sequentially deleted from the 5´-end was fused with the β−glucuronidase (GUS) reporter gene. The chimeric gene was introduced into calli derived from rice scutellum via Agrobacterium tumefaciens-mediated transformation and tissue-specific GUS activity determined in T0 generations. When the entire region was fused, GUS activity was detected in vascular bundles of the developing leaf blade and in dorsal and lateral vascular bundles of developing grains. This corresponds with our previous immunodetection of NADH–GOGAT protein (Hayakawa et al., Planta 193, 455–460, 1994). A series of deletion experiments showed that a 149-nucleotide region between –142 and +7 was essential for promoter activity in the NADH–GOGAT gene.