Laurence Hibrand-Saint Oyant

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.

Differential Recruitment of T- and IgA B-lymphocytes in the Developing Mammary Gland in Relation to Homing Receptors and Vascular Addressins

The mammary gland (MG) develops new vasculature and is colonized by lymphocytes, primarily T-cells, during pregnancy. In contrast, during lactation it is colonized primarily by IgA-containing B-cells (c-IgA cells). To explain this difference, we analyzed the spatiotemporal relationships between lymphocytes that expressed peripheral or mucosal homing receptors (HR) and the location of their vascular counterreceptors using quantitative immunohistochemical techniques. We observed that the density of β7+/CD3+ T-cells varied with the amount of the mucosal addressin cell adhesion molecule-1 (MAdCAM-1)-stained area. Both increased during pregnancy to peak at delivery, decreased rapidly in early lactation to a steady level in mid- and late lactation, and returned to resting values after weaning. Although 60% of these β7 +/CD3+ T-cells scattered in the epithelium co-expressed αEβ7, whereas the remaining 40% in association with blood vessels were α4β7, these results are consistent with a role of MAdCAM-1 in the localization of α4β7 + T-cells. In contrast to T-cells, β7 +/c-IgA+ B plasmablasts (∼ 30% of total c-IgA cells) were located at the alveolar confluence, and their numbers increased in mid- and late lactation when MAdCAM-1 density plateaued. However, both T-and B-cells decreased after weaning. These results show an association between MAdCAM-1 expression level and recruitment of T-cells that does not hold for c-IgA B cells. Furthermore, the recruitment and accumulation of α4β7 + c-IgA cells are reminiscent of locally produced chemoattractants.

A survey of flowering genes reveals the role of gibberellins in floral control in rose

Exhaustive studies on flowering control in annual plants have provided a framework for exploring this process in other plant species, especially in perennials for which little molecular data are currently available. Rose is a woody perennial plant with a particular flowering strategy—recurrent blooming, which is controlled by a recessive locus (RB). Gibberellins (GA) inhibit flowering only in non-recurrent roses. Moreover, the GA content varies during the flowering process and between recurrent and non-recurrent rose. Only a few rose genes potentially involved in flowering have been described, i.e. homologues of ABC model genes and floral genes from EST screening. In this study, we gained new information on the molecular basis of rose flowering: date of flowering and recurrent blooming. Based on a candidate gene strategy, we isolated genes that have similarities with genes known to be involved in floral control in Arabidopsis (GA pathway, floral repressors and integrators). Candidate genes were mapped on a segregating population, gene expression was studied in different organs and transcript abundance was monitored in growing shoot apices. Twenty-five genes were studied. RoFT, RoAP1 and RoLFY are proposed to be good floral markers. RoSPY and RB co-localized in our segregating population. GA metabolism genes were found to be regulated during floral transition. Furthermore, GA signalling genes were differentially regulated between a non-recurrent rose and its recurrent mutant. We propose that flowering gene networks are conserved between Arabidopsis and rose. The GA pathway appears to be a key regulator of flowering in rose. We postulate that GA metabolism is involved in floral initiation and GA signalling might be responsible for the recurrent flowering character.

Quantitative trait loci for flowering time and inflorescence architecture in rose

The pattern of development of the inflorescence is an important characteristic in ornamental plants, where the economic value is in the flower. The genetic determinism of inflorescence architecture is poorly understood, especially in woody perennial plants with long life cycles. Our objective was to study the genetic determinism of this characteristic in rose. The genetic architectures of 10 traits associated with the developmental timing and architecture of the inflorescence, and with flower production were investigated in a F1 diploid garden rose population, based on intensive measurements of phenological and morphological traits in a field. There were substantial genetic variations in inflorescence development traits, with broad-sense heritabilities ranging from 0.82 to 0.93. Genotypic correlations were significant for most (87%) pairs of traits, suggesting either pleiotropy or tight linkage among loci. However, non-significant and low correlations between some pairs of traits revealed two independent developmental pathways controlling inflorescence architecture: (1) the production of inflorescence nodes increased the number of branches and the production of flowers; (2) internode elongation connected with frequent branching increased the number of branches and the production of flowers. QTL mapping identified six common QTL regions (cQTL) for inflorescence developmental traits. A QTL for flowering time and many inflorescence traits were mapped to the same cQTL. Several candidate genes that are known to control inflorescence developmental traits and gibberellin signaling in Arabidopsis thaliana were mapped in rose. Rose orthologues of FLOWERING LOCUS T (RoFT), TERMINAL FLOWER 1 (RoKSN), SPINDLY (RoSPINDLY), DELLA (RoDELLA), and SLEEPY (RoSLEEPY) co-localized with cQTL for relevant traits. This is the first report on the genetic basis of complex inflorescence developmental traits in rose.

Genetic Engineering and Tissue Culture of Roses

The recent advances in rose genetics and in functional genetics described in the previous two chapters have improved our knowledge about interesting characteristics of the rose. Gene transfer technologies may facilitate the introgression of homologous or heterologous genes to improve major ornamental traits as e.g., scent, plant architecture and color as well as biotic and abiotic stress responses and yield. Genetic transformation of roses requires the availability of reliable protocols for in vitro culture, for the transfer of genes and for selection and regeneration of transgenic plants. As for many other ornamental crops, in vitro culture of roses can be used (i) for rapid multiplication of commercial cultivars, (ii) to produce healthyand diseasefree plants and finally (iii) as a source of explants for plant regeneration as a prerequisite for transformation techniques. In vitro propagation of roses is common practice, particularly for the propagation of pot roses. First reports of in vitro culture of rose (Rosa multiflora) were made by Elliot (1970). The methods of micro propagation of roses in vitro were reviewed several times (Skirvin et al., 1984; Rout et al., 1999; Borissova et al., 2000; Jabbarzadeh and Khosh-Khui, 2005; Pati et al., 2006). An efficient in vitro plant regeneration protocol with high multiplication rates is the ‘key’ technology for various biotechnological techniques such as multiplication of clonal plants, mutation breeding programs by exposing to irradiation or by somaclonal variation, and biolistic or Agrobacterium-mediated transformation. However, the wide range of explants and experimental approaches that have been employed with different rose species and cultivars strongly suggest that a universal, cultivar-independent method for the production of regenerating tissues, coupled with efficient conversion and ex vitro acclimation of regenerants, will be difficult