The TFL1 homologue KSN is a regulator of continuous flowering in rose and strawberry

Flowering is a key event in plant life, and is finely tuned by environmental and endogenous signals to adapt to different environments. In horticulture, continuous flowering (CF) is a popular trait introduced in a wide range of cultivated varieties. It played an essential role in the tremendous success of modern roses and woodland strawberries in gardens. CF genotypes flower during all favourable seasons, whereas once-flowering (OF) genotypes only flower in spring. Here we show that in rose and strawberry continuous flowering is controlled by orthologous genes of the TERMINAL FLOWER 1 (TFL1) family. In rose, six independent pairs of CF/OF mutants differ in the presence of a retrotransposon in the second intron of the TFL1 homologue. Because of an insertion of the retrotransposon, transcription of the gene is blocked in CF roses and the absence of the floral repressor provokes continuous blooming. In OF-climbing mutants, the retrotransposon has recombined to give an allele bearing only the long terminal repeat element, thus restoring a functional allele. In OF roses, seasonal regulation of the TFL1 homologue may explain the seasonal flowering, with low expression in spring to allow the first bloom. In woodland strawberry, Fragaria vesca, a 2-bp deletion in the coding region of the TFL1 homologue introduces a frame shift and is responsible for CF behaviour. A diversity analysis has revealed that this deletion is always associated with the CF phenotype. Our results demonstrate a new role of TFL1 in perennial plants in maintaining vegetative growth and modifying flowering seasonality

The continuous flowering gene in rose is a floral inhibitor

In rose, RoKSN, a TFL1 homologue, is a key regulator of continuous flowering. To study the function of this gene in planta, protocols of plant transformation are needed. We complemented tfl1 Arabidopsis mutants and ectopically expressed RoKSN in a continuous-flowering rose. In Arabidopsis, RoKSN complemented the tfl1 mutant by rescuing late flowering and indeterminate growth. In continuous-flowering rose, the ectopic expression of RoKSN led to the absence of flowering. In these transgenic roses, a study of genes implied in the floral regulation was carried out. The floral activator transcripts decreased whereas the FD transcription factor is up-regulated. We conclude that RoKSN is a floral repressor and could regulate the expression of transcripts as RoFT and RoFD. These results could strengthen a mechanism of competitive interactions of RoFT and RoKSN with a common partner, FD to move towards flowering or vegetative developments

RoKSN, a floral repressor, forms protein complexes with RoFD and RoFT to regulate vegetative and reproductive development in rose

FT/TFL1 family members have been known to be involved in the development and flowering in plants. In rose, RoKSN, a TFL1 homologue, is a key regulator of flowering, whose absence causes continuous flowering. Our objectives are to functionally validate RoKSN and to explore its mode of action in rose.We complemented Arabidopsis tfl1 mutants and ectopically expressed RoKSN in a continuous-flowering (CF) rose. Using different protein interaction techniques, we studied RoKSN interactions with RoFD and RoFT and possible competition. In Arabidopsis, RoKSN complemented the tfl1 mutant by rescuing late flowering and indeterminate growth. In CF roses, the ectopic expression of RoKSN led to the absence of flowering. Different branching patterns were observed and some transgenic plants had an increased number of leaflets per leaf. In these transgenic roses, floral activator transcripts decreased. Furthermore, RoKSN was able to interact both with RoFD and the floral activator, RoFT. Protein interaction experiments revealed that RoKSN and RoFT could compete with RoFD for repression and activation of blooming, respectively. We conclude that RoKSN is a floral repressor and is also involved in the vegetative development of rose. RoKSN forms a complex with RoFD and could compete with RoFT for repression of flowering

A high-quality sequence of Rosa chinensis to elucidate genome structure and ornamental traits

Rose is the worlds most important ornamental plant with economic, cultural and symbolic value. Roses are cultivated worldwide and sold as garden roses, cut flowers and potted plants. Rose has a complex genome with high heterozygosity and various ploidy levels. Our objectives were (i) to develop the first high-quality reference genome sequence for the genus Rosa by sequencing a doubled haploid, combining long and short read sequencing, and anchoring to a high-density genetic map and (ii) to study the genome structure and the genetic basis of major ornamental traits. We produced a haploid rose line from R. chinensis "Old Blush" and generated the first rose genome sequence at the pseudo-molecule scale (512 Mbp with N50 of 3.4 Mb and L75 of 97). The sequence was validated using high-density diploid and tetraploid genetic maps. We delineated hallmark chromosomal features including the pericentromeric regions through annotation of TE families and positioned centromeric repeats using FISH. Genetic diversity was analysed by resequencing eight Rosa species. Combining genetic and genomic approaches, we identified potential genetic regulators of key ornamental traits, including prickle density and number of flower petals. A rose APETALA2 homologue is proposed to be the major regulator of petals number in rose. This reference sequence is an important resource for studying polyploidisation, meiosis and developmental processes as we demonstrated for flower and prickle development. This reference sequence will also accelerate breeding through the development of molecular markers linked to traits, the identification of the genes underlying them and the exploitation of synteny across Rosaceae

Gibberellins regulate the transcription of the continuous flowering regulator, RoKSN, a rose TFL1 homologue

International audienceThe role of gibberellins (GAs) during floral induction has been widely studied in the annual plant Arabidopsis thaliana. Less is known about this control in perennials. It is thought that GA is a major regulator of flowering in rose. In spring, low GA content may be necessary for floral initiation. GA inhibited flowering in once-flowering roses, whereas GA did not block blooming in continuous-flowering roses. Recently, RoKSN, a homologue of TFL1, was shown to control continuous flowering. The loss of RoKSN function led to continuous flowering behaviour. The objective of this study was to understand the molecular control of flowering by GA and the involvement of RoKSN in this inhibition. In once-flowering rose, the exogenous application of GA(3) in spring inhibited floral initiation. Application of GA(3) during a short period of 1 month, corresponding to the floral transition, was sufficient to inhibit flowering. At the molecular level, RoKSN transcripts were accumulated after GA(3) treatment. In spring, this accumulation is correlated with floral inhibition. Other floral genes such as RoFT, RoSOC1, and RoAP1 were repressed in a RoKSN-dependent pathway, whereas RoLFY and RoFD repression was RoKSN independent. The RoKSN promoter contained GA-responsive cis-elements, whose deletion suppressed the response to GA in a heterologous system. In summer, once-flowering roses did not flower even after exogenous application of a GA synthesis inhibitor that failed to repress RoKSN. A model is presented for the GA inhibition of flowering in spring mediated by the induction of RoKSN. In summer, factors other than GA may control RoKSN

Widely tunable Tm:CaF2 laser in-band pumped by a fiber laser at 1610 nm

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Genetic determinism of prickles in rose

International audienceRose is one of the major ornamental plants. The selection of glabrous cultivars is an important breeding target but remains a difficult task due to our limited genetic knowledge. Our objective was to understand the genetic and molecular determinism of prickles. Using a segregating diploid rose F1 population, we detected two types of prickles (glandular and non-glandular) in the progeny. We scored the number of non-glandular prickles on the floral and main stems for three years. We performed QTL analysis and detected four prickle loci on LG1, 3, 4 and 6. We determined the credible interval on the reference genome. The QTL on LG3 is a major locus that controls the presence of prickles, and three QTLs (LG3, 4 and 1) may be responsible for prickle density. We further revealed that glabrous hybrids are caused by the combination of the two recessive alleles from both parents. In order to test whether rose prickles could originate from a ‘trichome-like structure,’ we used a candidate approach to characterize rose gene homologues known in Arabidopsis, involved in trichome initiation. Four of these homologues were located within the overlapping credible interval of the detected QTLs. Transcript accumulation analysis weakly supports the involvement of trichome homologous genes, in the molecular control of prickle initiation. Our studies provide strong evidence for a complex genetic determinism of stem prickle and could help to establish guidelines for glabrous rose breeding. New insights into the relationship between prickles and trichomes constitute valuable information for reverse genetic research on prickles

The Continuous Flowering Gene in Rose Is a Floral Inhibitor

International audienceIn rose, RoKSN, a TFL1 homologue, is a key regulator of continuous flowering. To study the function of this gene in planta, protocols of plant transformation are needed. We complemented tfl1 Arabidopsis mutants and ectopically expressed RoKSN in a continuous-flowering rose. In Arabidopsis, RoKSN complemented the tfl1 mutant by rescuing late flowering and indeterminate growth. In continuous-flowering rose, the ectopic expression of RoKSN led to the absence of flowering. In these transgenic roses, a study of genes implied in the floral regulation was carried out. The floral activator transcripts decreased whereas the FD transcription factor is up-regulated. We conclude that RoKSN is a floral repressor and could regulate the expression of transcripts as RoFT and RoFD. These results could strengthen a mechanism of competitive interactions of RoFT and RoKSN with a common partner, FD to move towards flowering or vegetative developments

Linearly-polarized high-power Raman fiber lasers near 1670 nm

International audienceWe developed linearly-polarized and diffraction-limited Raman fiber laser (RFL) sources in the 1650–1680 nm spectral range with up to 6.2 W of output power. The pump laser near 1550 nm is a MOPA consisting of a laser diode seed source and two amplifier stages based on different erbium-doped fibers. Two RFL configurations using a PM single-mode fiber as Raman gain fiber are demonstrated and laser performances are numerically simulated. The first is a free-running laser configuration achieving 6.25 W of output power at 1655 nm and a conversion efficiency of 79%. In the second scheme, an all-fibered RFL using fiber Bragg gratings and emitting 5 W of output power at 1679 nm is demonstrated. In the latter case, performances limitations due to spectral broadening are analyzed

The rose genome sequencing initiative.

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