The B2 flowering time locus of beet encodes a zinc finger transcription factor

Abstract

Sugar beet (Beta vulgaris) is a biennial root crop that grows vegetatively in the first year and starts shoot elongation (bolting) and flowering after exposure to cold temperatures over winter. Early bolting before winter is controlled by the dominant allele of the B locus. Recently, the BOLTING TIME CONTROL 1 (BTC1) gene has been cloned from this locus. BTC1 promotes early bolting through repression of the downstream bolting repressor B. vulgaris FLOWERING LOCUS T1 (BvFT1) and activation of the downstream floral activator BvFT2. We have identified a new bolting locus B2 acting epistatically to B. B2 houses a transcription factor which is diurnally regulated and acts like BTC1 upstream of BvFT1 and BvFT2. It was termed BvBBX19 according to its closest homolog from Arabidopsis thaliana. The encoded protein has two conserved domains with homology to zinc finger B-boxes. Ethyl methanesulfonate-induced mutations within the second B-box caused up-regulation of BvFT1 and complete down-regulation of BvFT2. In Arabidopsis, the expression of FT is promoted by the B-box containing protein CONSTANS (CO). We performed a phylogenetic analysis with B-box genes from beet and A. thaliana but only BvCOL1 clustered with CO. However, BvCOL1 had been excluded as a CO ortholog by previous studies. Therefore, a new model for flowering induction in beet is proposed in which BTC1 and BvBBX19 complement each other and thus acquire a CO function to regulate their downstream targets BvFT1 and BvFT2.winter beet | sucrose | map-based cloning

BBX19 Interacts with CONSTANS to RepressFLOWERING LOCUS TTranscription, Defining a Flowering Time Checkpoint inArabidopsis

“…Previously, BBX19 was reported to be a circadian-regulated gene with a function in the output pathway downstream of the clock (Kumagai et al, 2008;Dally et al, 2014). Our data corroborate the circadian regulation of BBX19 and further demonstrate its antiphasic circadian rhythm compared with those of FT and CO.…”

“…This suggests that BBX19 functions as a checkpoint to prevent the expression of FT soon after the onset of CO expression and the light-induced stabilization of its protein necessary for binding to the FT promoter. Intriguingly, the B2 flowering time locus of the biennial root crop sugar beet (Beta vulgaris) was recently identified as Bv-BBX19, a close homolog of Arabidopsis BBX19 (Dally et al, 2014). The authors reported that induced mutations within the second B-box of Bv-BBX19 caused the upregulation of FLOWERING LOCUS1 (Bv-FT1), and they further proposed a model of action by which Bv-BBX19 and BOLTING TIME CONTROL1 (BTC1) complement each other and thereby acquire a CO function to regulate the downstream Bv-FT1 and Bv-FT2 genes.…”

Winter Memory throughout the Plant Kingdom: Different Paths to Flowering

“…Recessive alleles of another bolting locus, called B2, confer a biennial behavior to plants homozygous for the annual allele BTC1 (Büttner et al, 2010). This locus encodes the DOUBLE B-BOX TYPE ZINC FINGER protein BvBBX19, which is orthologous to an Arabidopsis protein that negatively influences the induction of FT (Dally et al, 2014;Wang et al, 2014). Interestingly, the expression of both BvBBX19 and BvBTC1 is diurnally regulated (Pin et al, 2012;Dally et al, 2014), and although the functional relationship between these two proteins is still unclear, they both participate in the regulation of an antagonistic pair of FT-like proteins, BvFT1 and BvFT2 ( Fig.…”

“…Interestingly, the expression of both BvBBX19 and BvBTC1 is diurnally regulated (Pin et al, 2012;Dally et al, 2014), and although the functional relationship between these two proteins is still unclear, they both participate in the regulation of an antagonistic pair of FT-like proteins, BvFT1 and BvFT2 ( Fig. 1D; Pin et al, 2010Pin et al, , 2012Dally et al, 2014). The short-day-expressed BvFT1 represses floral transition and negatively influences BvFT2 levels, whose expression is promoted by long days (Pin et al, 2010).…”

Vernalisation mediated LncRNA-like gene expression in Beta vulgaris

“…Sugar beet (Beta vulgaris L.) is a biennial root crop that requires vernalisation to initiate the transition from vegetative to reproductive growth. Sugar beet is a member of the Amaranthaceae family that evolved from the monocot-dicot split~140 million years ago (Dally et al 2014). Two FLOWERING LOCUS T (FT) genes such as BvFT1 and BvFT2 of B. vulgaris had evolved antagonistic functions.…”