the aux iaa genes encode a large family of short lived proteins known to regulate auxin signalling in plants functional characterization of sliaa15 a member of the tomato solanum lycopersicum aux iaa family shows that the encoded protein acts as a strong repressor of auxin dependent transcription the physiological significance of sliaa15 was addressed by a reverse genetics approach revealing that sliaa15 plays multiple roles in plant developmental processes the sliaa15 down regulated lines display lower trichome number reduced apical dominance with associated modified pattern of axillary shoot development increased lateral root formation and decreased fruit set moreover the leaves of sliaa15 inhibited plants are dark green and thick with larger pavement cells longer palisade cells and larger intercellular space of spongy mesophyll cells the sliaa15 suppressed plants exhibit a strong reduction in type i v and vi trichome formation suggesting that auxin dependent transcriptional regulation is required for trichome initiation concomitant with reduced trichome formation the expression of some r2r3 myb genes putatively involved in the control of trichome differentiation is altered these phenotypes uncover novel and specialized roles for aux iaas in plant developmental processes clearly indicating that members of the aux iaa gene family in tomato perform both overlapping and specific functions.