FT overexpression induces precocious flowering and normal reproductive development in Eucalyptus

Abstract

SummaryEucalyptus trees are among the most important species for industrial forestry worldwide. However, as with most forest trees, flowering does not begin for one to several years after planting which can limit the rate of conventional and molecular breeding. To speed flowering, we transformed a Eucalyptus grandis 9 urophylla hybrid (SP7) with a variety of constructs that enable overexpression of FLOWERING LOCUS T (FT). We found that FT expression led to very early flowering, with events showing floral buds within 1-5 months of transplanting to the glasshouse. The most rapid flowering was observed when the cauliflower mosaic virus 35S promoter was used to drive the Arabidopsis thaliana FT gene (AtFT). Early flowering was also observed with AtFT overexpression from a 409S ubiquitin promoter and under heat induction conditions with Populus trichocarpa FT1 (PtFT1) under control of a heat-shock promoter. Early flowering trees grew robustly, but exhibited a highly branched phenotype compared to the strong apical dominance of nonflowering transgenic and control trees. AtFT-induced flowers were morphologically normal and produced viable pollen grains and viable self-and crosspollinated seeds. Many self-seedlings inherited AtFT and flowered early. FT overexpressioninduced flowering in Eucalyptus may be a valuable means for accelerating breeding and genetic studies as the transgene can be easily segregated away in progeny, restoring normal growth and form.

FLOWERING LOCUS T Triggers Early and Fertile Flowering in Glasshouse Cassava (Manihot esculenta Crantz)

“…To our knowledge, this is the first report of accelerated flowering and viable seed production in cassava using Arabidopsis FT . This study complements other reports of induced flowering [20,21,22,23,24,25,27], further highlighting the importance to continually develop efficient methods to foster flowering in cassava and other important crops. Similar to our grafting experiment, a recent field study also revealed a lack of flowering in non- or late-flowering cultivars grafted to rootstocks of a profuse, early flowering (non-transgenic) cultivar [28].…”

“…Once in the phloem, FT is translocated to the shoot apical meristem where interaction with the bZIP transcription factor FD and phospholipid phosphatidylcholine [16] results in nuclear localization and activation of LEAFY ( LFY ), APETALA1 ( AP1 ), and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 ( SOC1 ) to trigger flower development [17,18,19]. With improved understanding of flowering mechanisms, over-expression of FT has been exploited to induce precocious flowering in various plant species [20,21,22,23,24,25] thus enabling a more rapid and refined approach to breeding.…”

Virus-Induced Flowering: An Application of Reproductive Biology to Benefit Plant Research and Breeding

“…Overexpressing FT in trees such as eucalypts promotes flowering and yields fertile flowers with viable pollen and seeds ( Fig. 1; Klocko et al, 2016), but as with most transgenes, the threshold level of expression can be variable among events. Apple transformed with MdFT1, citrus transformed with CiFT, and plum (Prunus domestica) transformed with CiFT and PtFT yielded fertile flowers, pollen, and seeds, respectively (Endo et al, 2005;Kotoda et al, 2010;Tränkner et al, 2010;Srinivasan et al, 2012).…”

FT and florigen long-distance flowering control in plants

“…FT promoted flowering in Eucalyptus[45] as did expression from a heat-inducible promoter in juvenile poplar[43] (Figure 2) or by viral delivery into cotton, apple and pear [46,47,48,49 ]. Constitutive expression of poplar FT1 also gave early maturity and continuous flowering in plum [50] and its inducible expression promoted flowering in apple [51] (Figure 2).…”