Meristem activity during flower and ovule development in tomato is controlled by the mini zinc finger gene INHIBITOR OF MERISTEM ACTIVITY

Plants have the ability to form new organs as a result of indeterminate growth ensured by specific regions of pluripotent cells, called meristems. Flowers are produced by the activity of floral meristems which differ from vegetative meristems in their determinate fate. Transcriptional complexes associating C-, D- and E-type MADS box proteins are responsible for flower determinacy by controlling the stem cell population within the floral meristem. We report here that the INHIBITOR OF MERISTEM ACTIVITY (IMA) gene encoding a mini zinc finger (MIF) protein from tomato (Solanum lycopersicum) regulates the processes of flower and ovule development. IMA inhibits cell proliferation during floral termination, controls the number of carpels during floral development and acts as a repressor of the meristem organizing centre gene WUSCHEL. Underexpression of IMA prevents the formation of gametophytic tissue, which is replaced by an undetermined sporophytic tissue. Molecular analyses of MADS box gene expression revealed that IMA participates in the termination of floral meristems and initiation of ovule primordia by activating D- type gene expression. Taken together, our data indicate that both termination of floral meristems and differentiation of nucelli during ovule development require a similar mechanism involving the repression of WUSCHEL and the activation of D-class genes.