Development of a transgenic early flowering pear (Pyrus communis L.) genotype by RNAi silencing of PcTFL1-1 and PcTFL1-2

Abstract

Trees require a long maturation period, known as juvenile phase, before they can reproduce, complicating their genetic improvement as compared to annual plants. 'Spadona', one of the most important European pear (Pyrus communis L.) cultivars grown in Israel, has a very long juvenile period, up to 14 years, making breeding programs extremely slow. Progress in understanding the molecular basis of the transition to flowering has revealed genes that accelerate reproductive development when ectopically expressed in transgenic plants. A transgenic line of 'Spadona', named Early Flowering-Spadona (EF-Spa), was produced using a MdTFL1 RNAi cassette targeting the native pear genes PcTFL1-1 and PcTFL1-2. The transgenic line had three T-DNA insertions, one assigned to chromosome 2 and two to chromosome 14 PcTFL1-1 and PcTFL1-2 were completely silenced, and EF-Spa displayed an early flowering phenotype: flowers developed already in tissue culture and on most rooted plants 1-8 months after transfer to the greenhouse. EF-Spa developed solitary flowers from apical or lateral buds, reducing vegetative growth vigor. Pollination of EF-Spa trees generated normal-shaped fruits with viable F1 seeds. The greenhouse-grown transgenic F1 seedlings formed shoots and produced flowers 1-33 months after germination. Sequence analyses, of the non-transgenic F1 seedlings, demonstrated that this approach can be used to recover seedlings that have no trace of the T-DNA. Thus, the early flowering transgenic line EF-Spa obtained by PcTFL1 silencing provides an interesting tool to accelerate pear breeding.

Three FT and multiple CEN and BFT genes regulate maturity, flowering, and vegetative phenology in kiwifruit

“…In addition to regulation of flowering, poplar FT - and TFL1 / CEN -like genes are implicated in the regulation of vegetative to reproductive transition, growth and dormancy cycles, and the co-existence of vegetative and floral meristems on the same shoot (Böhlenius et al , 2006; Hsu et al , 2006, 2011; Rinne et al , 2011). Similarly, TFL1 is a key regulator of perennial growth and seasonality of flowering in strawberry and rose (Iwata et al , 2012; Koskela et al , 2012, 2016; Randoux et al , 2014; Rantanen et al , 2015), down-regulation of TFL1 -like genes accelerated flowering in apple and pear (Kotoda et al , 2006; Freiman et al , 2012; Yamagishi et al , 2016), ectopic overexpression of a CEN homolog suppressed flowering in kiwifruit (Varkonyi-Gasic et al , 2013), and a connection of TFL1 accumulation with biennial bearing in apple has been established (Haberman et al , 2016). …”

Strawberry homologue of TERMINAL FLOWER1 integrates photoperiod and temperature signals to inhibit flowering

“…In several species of the Rosaceae family, homologues of TFL1 are strong repressors of flowering, which determine the timing of seasonal flower initiation (Kotoda et al, 2006;Flachowsky et al, 2012;Freiman et al, 2012;Iwata et al, 2012;Koskela et al, 2012). Based on our previous studies (Koskela et al, 2012;Mouhu et al, 2013;Rantanen et al, 2014) and results presented here, we propose the following model on the integration of environmental signals by FvTFL1 (Figure 6).…”

“…The expression of FvFT1 and FvSOC1 correlates negatively with flowering because the MADS domain transcription factor FvSOC1 activates the mRNA expression of the strong floral repressor FvTFL1 in the shoot apex (Koskela et al, 2012;Mouhu et al, 2013). TFL1 homologues function as major repressors of flowering also in other perennials including apple (Kotoda et al, 2006;Flachowsky et al, 2012), pear (Freiman et al, 2012), rose (Iwata et al, 2012) and Populus (Mohamed et al, 2010).…”

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

“…TERMINAL FLOWER1 (TFL1) is in the same gene family as FT, but TFL1 (and homologs) acts as a competitive inhibitor of FT (Hanano and Goto, 2011;Ho and Weigel, 2014;Lifschitz et al, 2014). Consequently, either FT gain of function or TFL1 loss of function results in more determinate growth and faster transition to reproductive growth (Flachowsky et al, 2012;Freiman et al, 2012). Other genes in the flowering pathway are used similarly as breeding tools to accelerate flowering; for example, apple transformed with a flowering-associated MADS box gene from silver birch (Betula spp.…”