Coi1-Dependent Signaling Pathway Is Not Required for Mi-1—Mediated Potato Aphid Resistance

Tomato (Solanum lycopersicum) has a unique resistance gene, Mi-1, that confers resistance to animals from distinct taxa, nematodes, and piercing and sucking insects. Mi-1 encodes a protein with a nucleotide-binding site and leucine-rich repeat motifs. Early in the potato aphid (Macrosiphum euphorbiae)—tomato interactions, aphid feeding induces the expression of the jasmonic acid (JA)-regulated proteinase inhibitor genes, Pin1 and Pin2. The jai1-1 (jasmonic acid insensitive 1) tomato mutant, which is impaired in JA perception, was used to gain additional insight into the JA signaling pathway and its role in the Mi-1—mediated aphid resistance. The jai1-1 mutant has a deletion in the Coi1 gene that encodes a putative F-box protein. In this study, aphid colonization, survival, and fecundity were compared on wild-type tomato and jai1-1 mutant. In choice assays, the jai1-1 mutant showed higher colonization by potato aphids compared with wild-type tomato. In contrast, no-choice assays showed no difference in potato aphid survival or fecundity between jai1-1 and the wild-type parent. Plants homozygous for Mi-1 and for the jai1 mutation were not compromised in resistance to potato aphids, using either choice or no-choice assays. In addition, the accumulation of JA-regulated Pin1 transcripts after aphid feeding was Coi1 dependent. Taken together, these data indicate that, although potato aphids activate Coi1-dependent defense response in tomato, this response is not required for Mi-1—mediated resistance to aphids.