Auxin is a central hormone that exerts pleiotropic effects on plant growth 
including the development of roots, shoots, flowers and fruit. The perception 
and signaling of the plant hormone auxin rely on the cooperative action of 
several components, among which auxin/indole-3-acetic acid (Aux/IAA) proteins 
play a pivotal role. In this study, we identified and comprehensively analyzed 
the entire Aux/IAA gene family in tomato (Solanum lycopersicum), a reference 
species for Solanaceae plants, and the model plant for fleshy fruit development. 
Functional characterization using a dedicated single cell system revealed that 
tomato Aux/IAA proteins function as active repressors of auxin-dependent gene 
transcription, with, however, different Aux/IAA members displaying varying 
levels of repression. Phylogenetic analysis indicated that the Aux/IAA gene 
family is slightly contracted in tomato compared with Arabidopsis, with a lower 
representation of non-canonical proteins. Sl-IAA genes display distinctive 
expression pattern in different tomato organs and tissues, and some of them 
display differential responses to auxin and ethylene, suggesting that Aux/IAAs 
may play a role in linking both hormone signaling pathways. The data presented 
here shed more light on Sl-IAA genes and provides new leads towards the 
elucidation of their function during plant development and in mediating hormone 
cross-talk.