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

Abstract

SUMMARYPhotoperiod and temperature are major environmental signals affecting flowering in plants. Although molecular pathways mediating these signals have been well characterized in the annual model plant Arabidopsis, much less information is known in perennials. Many perennials including the woodland strawberry (Fragaria vesca L.) are induced to flower in response to decreasing photoperiod and temperature in autumn and they flower following spring. We showed earlier that, in contrast with Arabidopsis, the photoperiodic induction of flowering in strawberry occurs in short days (SD) when the decrease in FvFT1 (FLOWERING LOCUS T) and FvSOC1 (SUPPRESSOR OF THE OVEREXPRESSION OF CONSTANS1) expression leads to lower mRNA levels of the floral repressor, FvTFL1 (TERMINAL FLOWER1). By using transgenic lines and gene expression analyses, we show evidence that the temperature-mediated changes in the FvTFL1 mRNA expression set critical temperature limits for the photoperiodic flowering in strawberry. At temperatures below 13°C, low expression level of FvTFL1 in both SD and long days (LD) allows flower induction to occur independently of the photoperiod. Rising temperature gradually increases FvTFL1 mRNA levels under LD, and at temperatures above 13°C, SD is required for the flower induction that depends on the deactivation of FvSOC1 and FvTFL1. However, an unknown transcriptional activator, which functions independently of FvSOC1, enhances the expression of FvTFL1 at 23°C preventing photoperiodic flowering. We suggest that the observed effect of the photoperiod 3 temperature interaction on FvTFL1 mRNA expression may allow strawberry to induce flowers in correct time in different climates.

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). …”

Additive QTLs on three chromosomes control flowering time in woodland strawberry (Fragaria vesca L.)

“…On the basis of the evidence shown here, identified QTLs control flowering time additively along with a previously identified floral repressor FvTFL1 that has quantitative effect on flowering time. As TFL1 homologs likely integrate both light and temperature signals to control flowering time in woodland and cultivated strawberries, 39,43 we suggest that candidate genes on the LG4 and LG7 QTL regions may control flowering time through TFL1 . However, further studies are needed to clarify causal genes and to reveal their roles in the control of flowering time and vegetative traits.…”

“…Among these regulators, the expression of FT1 and SOC1 homologs correlate with TFL1 mRNA levels only in specific conditions in woodland and cultivated strawberries suggesting that TFL1 alleles or its other regulators should be major targets of future investigations. 39,43 Whether some of the candidate genes identified in this study control flowering time through FvTFL1 is an interesting open question.…”

“…However, at temperatures above 20 °C FvTFL1 is highly upregulated by an unknown activator that functions independently of FvSOC1, and plants remain vegetative. 37,39 This model contrasts with the mechanism in Arabidopsis in which both FT and SOC1 function as floral activators. 1 However, FvFT1 is a strong floral activator in EB woodland strawberries that are lacking functional FvTFL1 .…”

The hot, the cold and the tulip : the regulation of flowering time and dormancy release

“…In the dicot Arabidopsis, TFL1 also acts as a flowering repressor in the ambient temperature pathway and was identified as hub between the photoperiodic and ambient temperature pathways (Strasser et al, 2009). Also in Fragaria vesca (strawberry) the AtTFL1 homologue FvTFL1 integrates photoperiod and temperature signals in order to repress flowering (Rantanen et al, 2015). Different from Arabidopsis and strawberry, tulip is a day neutral plant and therefore, photoperiod is not supposed to play a role in the regulation of flowering time .…”