Isolation and expression analysis of FLOWERING LOCUS T-like and gibberellin metabolism genes in biennial-bearing mango trees

Mango (Mangifera indica L.) is one of the most important evergreen fruit trees, but it has a high tendency of biennial bearing because of irregular flowering. In this study, a FLOWERING LOCUS T-like (FT-like) gene was isolated from mango (MiFT) and characterized. The deduced amino acid sequence of MiFT showed high identity of the gene to other plant FT-like genes, and further, MiFT expression increased only in the leaves under floral-inductive conditions. Comparison of heavy crop load (HC) and no crop load (NC) mango trees showed that MiFT expression strongly increased only in NC trees under cool temperature. In NC trees, almost all the apical buds formed panicles, whereas in HC trees, only a few panicles were produced in the next season of fruit set. Further, HC trees had lower starch content in the shoots than NC trees. Furthermore, application of 250-ppm gibberellin 3 (GA3) completely inhibited flowering and MiFT expression in both HC and NC trees. GA metabolism genes were also isolated from mango and their expression patterns were investigated. Gibberellin-3-oxidase (GA3-ox) controls the final step of biosynthesis of active GA, and its gene expression surged only in HC trees under cool temperature. In conclusion, MiFT is considered a key factor in mango flowering, and regulation of MiFT expression through GA metabolism was discussed.