De novo organogenesis relies on the capacity to regenerate in vitro the entire plant from single somatic cells and it is the most common pathway leading to in vitro plant regeneration. This capacity is frequently used in biotechnological breeding and in vitro plant tissue culture. Organogenesis is highly dependent on phytohormone perception and can be divided in acquisition of competence, organ induction and morphological differentiation phases. Recent studies on cell signaling that initiates the regeneration process have allowed the detection of genes and signaling molecules related mainly to the induction of new organs phase. The assignment of the shoot identity to the developing primordia is controlled by cytokinin and involves the expression of meristem identity genes, like WUSCHEL (WUS). However, the molecular mechanisms involved in the acquisition of competence are less understood. The founder cell specification, the development of primordia (organogenic callus) and the acquisition of organogenesis competence are mediated by auxin and related with CUP-SHAPED COTYLEDON2 (CUC2) gene expression. These advances was almost completely based on Arabidopsis thaliana studies, but important crops does not strictly follow the Arabidopsis well explored model: The tomato Solanum lycopersicum, cultivar Micro-Tom (MT), has not the ability to regenerate shoots on root explants neither on induced callus. In MT, two genes potentially involved in the control of competence are PROCERA (PRO) and REGENERATION1 (RG1), indicating a common competence between root and shoot organogenesis. My early results define temporally the acquisition of competence and induction of organogenesis phases and macroscopically evidence the influence of auxin and cytokinins during MT regeneration process. However, hormonal and genetic mechanisms involved in tomato organogenesis remain unclear. Thus, through investigation of hormonal and organogenesis-related genes fused to reporter genes coupled with high resolution live imaging, the goal of this project is to delineate spatio-temporally the mechanism of de novo organogenesis in MT and establish the molecular differences between patterns of development involved in tomato and Arabidopsis regeneration processes.
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