MINIPROTEINS AS CONTROLLING FACTORS IN REPRODUCTIVE DEVELOPMENT

Fruit set is dependent on successful fertilization and is subjected to many genetic factors as well as environmental conditions. Not only classical hormones and transcription factors orchestrate this process, also several miniproteins can participate in the flowering and fruit set. A recent study demonstrated the involvement of a class of Solanaceae-specific cystine-knot miniproteins, named TCMPs in the fruit set of Solanum lycopersicum (Molesini et al,2018). The tomato TCMP-1 and TCMP-2 share with the other cystineknot miniproteins a unique three-dimensional structure characterized by three intra-molecular disulfide bonds forming a cystine-knot. The expression pattern of TCMPs is tightly regulated during flower and fruit development. TCMP-1 is highly expressed in flower buds before anthesis whereas TCMP-2 is poorly expressed before anthesis and then, the expression level gradually increases reaching the maximum expression in the mature fruit. To investigate their function, the endogenous level of these genes was altered generating transgenic plants expressing the TCMP-1 coding sequence under the control of the TCMP-2 promoter (TCMP-2p:TCMP-1). The expression of the transgene caused an earlier fruit setting with no visible phenotypic effects on vegetative growth associated with an increased expression of TCMP-2 in pre-anthesis flower buds. This suggests to us a possible important involvement of these genes in the early stage of flower/fruit development.