Life cycle adaptation to latitudinal and seasonal variation in photoperiod and temperature is a major determinant of evolutionary success in flowering plants. Whereas the life cycle of the dicotyledonous model species Arabidopsis thaliana is controlled by two epistatic genes, FLOWERING LOCUS C and FRIGIDA, three unrelated loci (VERNALIZATION) determine the spring and winter habits of monocotyledonous plants such as temperate cereals. In the core eudicot species Beta vulgaris, whose lineage diverged from that leading to Arabidopsis shortly after the monocot-dicot split 140 million years ago, the bolting locus B is a master switch distinguishing annuals from biennials. Here, we isolated B and show that the pseudo-response regulator gene BOLTING TIME CONTROL 1 (BvBTC1), through regulation of the FLOWERING LOCUS T genes, is absolutely necessary for flowering and mediates the response to both long days and vernalization. Our results suggest that domestication of beets involved the selection of a rare partial loss-of-function BvBTC1 allele that imparts reduced sensitivity to photoperiod that is restored by vernalization, thus conferring bienniality, and illustrate how evolutionary plasticity at a key regulatory point can enable new life cycle strategies.

The transition from vegetative growth to reproductive development is a complex process that requires an integrated response to multiple environmental cues and endogenous signals. In Arabidopsis thaliana, which has a facultative requirement for vernalization and long days, the genes of the autonomous pathway function as floral promoters by repressing the central repressor and vernalization-regulatory gene FLC. Environmental regulation by seasonal changes in daylength is under control of the photoperiod pathway and its key gene CO. The root and leaf crop species Beta vulgaris in the caryophyllid clade of core eudicots, which is only very distantly related to Arabidopsis, is an obligate long-day plant and includes forms with or without vernalization requirement. FLC and CO homologues with related functions in beet have been identified, but the presence of autonomous pathway genes which function in parallel to the vernalization and photoperiod pathways has not yet been reported. Here, this begins to be addressed by the identification and genetic mapping of full-length homologues of the RNA-regulatory gene FLK and the chromatin-regulatory genes FVE, LD, and LDL1. When overexpressed in A. thaliana, BvFLK accelerates bolting in the Col-0 background and fully complements the late-bolting phenotype of an flk mutant through repression of FLC. In contrast, complementation analysis of BvFVE1 and the presence of a putative paralogue in beet suggest evolutionary divergence of FVE homologues. It is further shown that BvFVE1, unlike FVE in Arabidopsis, is under circadian clock control. Together, the data provide first evidence for evolutionary conservation of components of the autonomous pathway in B. vulgaris, while also suggesting divergence or subfunctionalization of one gene. The results are likely to be of broader relevance because B. vulgaris expands the spectrum of evolutionarily diverse species which are subject to differential developmental and/or environmental regulation of floral transition.

Using a co-dominant genotypic PCR marker we show for the first time that, in sugar beet, the GA and B-gene pathways are independent for bolt initiation. We show that vernalization permits GA-dependant stem elongation and that the B-allele influences subsequent flowering.

Seed production in hybrid crops such as sugar beet (Beta vulgaris ssp. vulgaris) is greatly facilitated by synchronous flowering times of the hybrid parents. In the model species Arabidopsis thaliana, many of the genes that control flowering time have been identified, but knowledge of the genetic and molecular basis of flowering time control in sugar beet is just beginning to emerge. To start deciphering the genetic landscape of flowering time control in cultivated biennial beets after vernalization over winter, we developed multi-parent QTL populations derived from five breeding lines. Three partially inbred lines were used to generate two segregating populations. One parent was in common. The other segregating populations comprised three full-sib families based on heterozygous parents. The parents spanned a wide range of flowering characteristics and depicted the range of flowering times that can be expected in a common sugar beet breeding population. The offspring (F1) The difference between the two years we suppose was due to the very hot April in 2007 in Provence, France. The April 2007 displayed a mean temperature that was 6 °C higher than average. This led to a strong year but supposedly also to a strong genotype*year interaction. The year effect was 6.2 days for BF and 2.2 days for FF, resp..For genetic map construction and QTL mapping, the individual F2 plants were genotyped with 173 EST-derived SNP markers. In addition, we developed markers for a total of 14 recently described flowering time genes in B. vulgaris or candidate genes which were identified on the basis of homology to floral regulators in A. thaliana. Candidate genes included floral integrators and homologs of key genes in the major floral regulatory pathways. Ten of these genes were