Cloning and expression analysis of LeTIR1 in tomato

The full-length cDNA of LeTIR1 gene was isolated from tomato with EST-based in silico cloning followed by RACE amplification. LeTIR1 contained an open reading frame (ORF) 1872 bp long, encoding 624 amino acid residues. The predicted protein LeTIR1 had one F-box motif and eleven leucine-rich repeats (LRRs), all of which are highly conserved in TIR1 proteins of other plant species. Phylogenetic analysis showed that the LeTIR1 protein shared high similarity with other known TIR1 proteins. Both sequence and phylogenetic analysis suggested that LeTIR1 is a TIR1 homologue and encodes an F-box protein in tomato. Semi-quantitative RT-PCR indicated that LeTIR1 was expressed constitutively in all organs tested, with higher expression in stem than root, leaf, flower and fruit. Its expression level was positively correlated with the auxin distribution in stem or axillary shoot, and was induced by spraying exogenous IAA.