Two CONSTANS-LIKE genes jointly control flowering time in beet

Abstract

Breeding vegetative crops (e.g. beets, cabbage, forage grasses) is challenged by two conflicting aims. For field production, flowering must be avoided while flowering and seed set is necessary for breeding and seed production. The biennial species sugar beet makes shoot elongation (‘bolting’) followed by flowering after a long period of cold temperatures. Field production in northern geographical regions starts in spring. A thickened storage root is formed only during vegetative growth. It is expected that winter beets, which are sown before winter would have a much higher yield potential. However, field production was not possible so far due to bolting after winter. We propose a strategy to breed winter beets exploiting haplotype variation at two major bolting time loci, B and B2. Both genes encode transcription factors controlling the expression of two orthologs of the Arabidopsis gene FLOWERING LOCUS T (FT). We detected an epistatic interaction between both genes because F2 plants homozygous for two B/B2 mutant alleles did not bolt even after vernalization. Fluorescence complementation studies revealed that both proteins form a heterodimer in vivo. In non-bolting plants, the bolting activator BvFT2 was completely downregulated whereas the repressor BvFT1 was upregulated which suggests that both genes acquire a CONSTANS (CO) like function in beet. Like CO, B and B2 proteins house CCT and BBX domains which, in contrast to CO are split between the two beet genes. We propose an alternative regulation of FT orthologs in beet that can be exploited to breed winter beets.

Evolutionary processes from the perspective of flowering time diversity

“…One gain of this function by CO likely occurred through coding and cis‐ regulatory changes following gene duplication near the origin of the Brassicaceae, as the sole CO homolog in the Cleomaceae, the sister clade to the Brassicaceae, functions similar to COL1 and COL2 , two CO paralogs that have circadian functions but do not impact photoperiodic flowering in A. thaliana (Simon et al , ) . Finally, in a particularly striking instance of convergent evolution, two independently transcribed genes, each of which encodes one of the two major protein functional domains found in CO , physically interact to regulate FT paralogs in sugar beet in a photoperiod‐dependent manner (Dally et al , ).…”

Prospects for the accelerated improvement of the resilient crop quinoa

“…In addition, several species, including Beta vulgaris , contain two orthologues of FT genes, FT1 and FT2 . While BvFT2 promotes flowering, BvFT1 acts antagonistically, repressing flowering before vernalization ( Dally et al , 2018 ). Of the four FT homologues expressed in quinoa, AUR62000271 and AUR62006619 are orthologues of BvFT2 , making them the best targets to promote early flowering in quinoa through overexpression strategies.…”

Validation of suitable genes for normalization of diurnal gene expression studies inChenopodium quinoa

“…quinoa to normalize the expression of saponin biosynthesis genes after methyl jasmonate treatment [23]. In beet, BBX19 acts together with BOLTING TIME CONTROL 1 (BTC1) in the circadian regulation of the flowering pathway [33] and shows diurnal regulation with an expression peak at dawn [20] . Considering the close phylogenetic relationship between B. vulgaris and C. quinoa, CqBBX19 might similarly regulate the flowering time in quinoa through photoperiod pathway.…”