Regulation of Floral Induction in Citrus

In the citrus industry, juvenility and alternate bearing are serious problems that cause lengthening of the breeding cycle and instability of annual fruit production, respectively. Both phenomena are closely related to flowering behavior: juvenility is caused by suppression of flowering in young plants and alternate bearing mainly results from suppression of flowering by fruit production. Many researchers have conducted studies into citrus flowering in a quest to resolve these problems. In recent years, molecular and genetic approaches to studying citrus flowering have been performed on the basis of studies on flowering-related genes in Arabidopsis. In Arabidopsis, the protein encoding a flowering-related gene, FLOWERING LOCUS T (FT), plays an important role in the promotion of flowering. Similarly, a citrus orthologue of FT (CiFT) has been confirmed to have a function in the promotion of flowering in citrus. In studies of transgenic plants, a CiFT co-expression vector has been already used to shorten the juvenile phase of citrus. In addition, endogenous expression of CiFT is closely correlated with flowering under various conditions, suggesting that endogenous CiFT may regulate floral induction. Considering the accumulating data, the regulation of CiFT expression is hypothesized to be essential to understand the mechanism of citrus flowering and studies on CiFT are expected to contribute to the resolution of flowering-related problems in citrus.