Differential expression of TIR-like genes embedded in the M1-1 gene cluster in nematode-resistant and -susceptible tomato roots

Transport inhibitor 1 (TIR1) is an auxin receptor that plays a pivotal role in auxin signaling. It has been reported that TIR-like genes are present in a gene cluster carrying the Mi-1 gene which confers resistance to nematodes, aphids and whiteflies. Since auxin is involved in the pathogenicity of tumor-inducing pathogens like nematodes, the co-localization of TIR-like genes with the Mi-1 gene may imply a role for TIR-like genes in the resistance conferred by the Mi-1 gene. In this study, we monitored the TIR-like transcript abundance (TTA) in both roots and leaves of nematode-resistant and –susceptible tomato lines. Our results demonstrate that TTA in roots, but not in leaves, was lower in nematode-resistant tomatoes than that in nematode-susceptible ones. In order to test whether the TIR-like genes are involved in nematode resistance mediated by the Mi-1 gene, we transiently silenced the Mi-1 gene homologues in a nematode-resistant tomato line and then measured TTA. Results showed that knocking down the expression of the Mi-1 gene homologues had no effect on TTA, therefore, we concluded that involvement of TIR-like genes in the response of tomato roots to nematodes is probably independent of the Mi-1 gene homologues. Further, we propose a possible explanation for the association between TTA and resistance to root-knot nematodes in tomato