Abstract

Summary Fruit ripening in tomato ( S olanum lycopersicum L .) is well understood at the molecular level. However, information regarding genetic pathways associated with tomato ovary and early fruit development is still lacking. Here, we investigate the possible role(s) of the micro RNA 156/ SQUAMOSA promoter‐binding protein‐like ( SPL or SBP box) module (mi R 156 node) in tomato ovary development. mi R 156‐targeted S . lycopersicum SBP genes were dynamically expressed in developing flowers and ovaries, and mi R 156 was mainly expressed in meristematic tissues of the ovary, including placenta and ovules. Transgenic tomato cv. M icro‐ T om plants over‐expressing the At MIR 156b precursor exhibited abnormal flower and fruit morphology, with fruits characterized by growth of extra carpels and ectopic structures. Scanning electron microscopy and histological analyses showed the presence of meristem‐like structures inside the ovaries, which are probably responsible for the ectopic organs. Interestingly, expression of genes associated with meristem maintenance and formation of new organs, such as L e T 6 / TKN 2 (a KNOX ‐like class I gene) and GOBLET (a NAM / CUC ‐like gene), was induced in developing ovaries of transgenic plants as well as in the ovaries of the natural mutant Mouse ear ( M e ), which also displays fruits with extra carpels. Conversely, expression of the MADS box genes MACROCALYX ( MC ) and FUL 1 / TDR 4 , and the LEAFY ortholog FALSIFLORA , was repressed in the developing ovaries of miR156 over‐expressors, suggesting similarities with Arabidopsis at this point of the mi R 156/ SPL pathway but with distinct functional consequences in reproductive development. Altogether, these observations suggest that the mi R 156 node is involved in maintenance of the meristematic state of ovary tissues, thereby controlling initial steps of fleshy fruit development and determinacy.