Regulation of Floral Induction in Citrus

Abstract

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.

Predicting the Number of Flowers in Satsuma Mandarin (<i>Citrus unshiu</i> Marc.) Trees Based on Citrus <i>FLOWERING LOCUS T</i> mRNA Levels

“…2A, B, see all markers without distinction). As we previously reported (Nishikawa, 2013;Nishikawa et al, 2012Nishikawa et al, , 2016, trees with low CiFT mRNA levels in November bore few flowers the following spring, while trees in which CiFT was highly expressed produced more flowers. The relationship between CiFT mRNA level and number of flowers per 100 nodes showed an exponential pattern.…”

“…Fruit production is also a factor that suppresses floral induction. In citrus trees, CiFT expression levels in the fall and winter are negatively correlated with the number of fruits produced, but positively correlated with the number of flowers the following spring (Nishikawa, 2013;Nishikawa et al, 2012Nishikawa et al, , 2016. Furthermore, CiFT expression and floral induction are enhanced by drought stress (Chica and Alberigo, 2013), and suppressed by gibberellin treatment (GoldbergMoeller et al, 2013;Muñoz-Fambuena et al, 2012).…”

“…Differences in these factors lead to considerable variability in the number of flowers among years (Nishikawa, 2013). Fluctuations in the number of flowers can result in considerable differences in fruit yields between growing seasons, which is a major problem in the citrus industry.…”

“…A previous study concluded that a citrus floweringrelated gene, FLOWERING LOCUS T (CiFT), influences seasonal floral induction (Nishikawa, 2013). This gene promotes floral induction, and transgenic citrus trees expressing CiFT exhibit a shortened juvenile period (Endo et al, 2005).…”

The Effect of Fruit Bearing on Low-molecular-weight Metabolites in Stems of Satsuma Mandarin (<i>Citrus unshiu</i> Marc.)

“…It has been indicated that citrus FLOWERING LOCUS T (CiFT) plays an important role in the flowering of citrus and that fruit bearing suppresses floral induction via the suppression of CiFT expression (Nishikawa, 2013;Nishikawa et al, 2007Nishikawa et al, , 2012. In recent years, transcriptomic and proteomic analyses have been conducted regarding alternate bearing in citrus (Muñoz-Fambuena et al, 2013a, b;Shalom et al, 2012Shalom et al, , 2014.…”