Expression of a FLOWERING LOCUS T homologue is temporally associated with annual flower bud initiation in Eucalyptus globulus subsp. globulus (Myrtaceae)

Abstract

The transition to flowering in plants is the result of the balance of endogenous processes and environmental signals that act through a complex genetic pathway that has been studied extensively in annual plants such as Arabidopsis. Perennial trees are characterised by a juvenile non-flowering phase lasting several years followed by an adult phase in which there is repeated cycling between vegetative and reproductive growth. The genetic control of flowering time is potentially more complex in perennials than in annuals and is less understood. Here, we examine the control of flowering in Eucalyptus globulus subsp. globulus, an important forestry species in temperate parts of the world. The E. globulus subsp. globulus homologues of two important flowering genes FLOWERING LOCUS T (FT) and LEAFY (LFY) were isolated and quantitative RT-PCR was used to measure their expression over a 2-year period. The expression of the homologue of FT in E. globulus subsp. globulus leaves was associated with the annual transition from vegetative to reproductive growth (i.e. flower bud initiation). Expression of the LFY homologue was associated with early flower bud development. In a comparison of FT and LFY expression patterns in two clones each of an early and late anthesis genotype, no association between the expression of these genes and the timing of anthesis was shown. Taken together, this indicates that FT and LFY could form part of the flower initiation pathway in Eucalyptus but do not regulate the observed differences in anthesis time.