Identification of a gene involved in the juvenile-to-adult transition (JAT) in cultivated olive trees

The juvenile-to-adult transition is a complex and poorly understood process in plant development required to reach reproductive competence. For woody plants, knowledge of this transition is even scantier and no genes have been definitively identified as involved in this transition. To search for genes involved in the juvenile-to-adult transition in olive, we constructed juvenile and adult subtractive cDNA gene libraries and identified genes that were differentially expressed in the juvenile and adult phases. In the analysis of theses libraries, we found 13 differentially expressed genes. One of these genes designated as juvenile to adult transition (JAT) was of special interest because it was highly expressed at the mRNA level in the early developmental phases but repressed in the adult phase. The analysis of mutant trees altered in the juvenile-to-adult transition, as well as a segregating progeny of 31 trees from a “Picual” x “Jabaluna” cross, support the contention that its activity might be required for a non-delayed transition. The study of an Arabidopsis thaliana JAT mutant strain confirmed this hypothesis as it showed a delayed flowering phenotype. JAT is expressed in different parts of the plant, showing an unexpectedly high level of mRNA in the roots. However, the JAT expression level is not determined by the distance to the roots, but rather depends on the developmental stage of the branch meristems. JAT is a widely represented gene in plants that appears to be involved in the control of the juvenile-to-adult transition in olive.