Flowering genes modulate plant tolerance to virus infection

Tolerance is a major defence response of plants to parasites that results in a lower impact of infection at similar parasite loads in tolerant than in non-tolerant host genotypes. The genetic basis of plant tolerance to viruses is poorly understood. We have shown before that tolerance of Arabidopsis thaliana to its relevant pathogen cucumber mosaic virus (CMV) is achieved through changes in host life-history traits upon infection that result in delaying flowering and re-allocating resources from vegetative growth to reproduction. In the present study we identify genetic determinants of tolerance which co-locate with three flowering repressor genes, FLC, FRI and HUA2. Analyses of genotypes carrying functional or non-functional alleles at these genes showed that functional alleles of FLC together with FRI and/or HUA2, were required both for tolerance and resource reallocation from growth to reproduction. Although tolerance is associated with a delay in flowering that allows resource reallocation, our results indicate that FLC regulates tolerance and flowering initiation by different mechanisms.The role of FLC in A. thaliana tolerance to CMV is a novel, major finding, that opens a new avenue of research on the interplay between defence and development in plants.