Flowering plants return to the sea…

International audienceFrom 18 to 22 June this year, around 120 fans of floral biology met at Hyères-les-Palmiers on the French Côte d'Azur for the latest in a series of two-yearly workshops on 'Molecular Mechanisms Controlling Flower Development'. These international meetings usually take place somewhere on the Mediterranean coast, and Hyères provided an idyllic setting in which to meet up with colleagues and discuss science on the beach as well as in the lecture hall or poster room. One flowering plant that really did return to the sea, Posidonia oceanica, was to be found growing in the shallow coastal waters surrounding the conference venue, and many delegates could be seen splashing about and (no doubt) thoroughly investigating this marine monocot between scientific sessions. The workshop, of which details can be found at: http:// www.ens-lyon.fr/RDP/FlowerWorkshop2019/, was divided into seven oral sessions and formatted so that a maximum number of speakers could present their data in 20 min highlighted talks, 15 min standard talks, or 4 min 'flash posters'. In all, 74 oral presentations were made, involving nearly two-thirds of delegates, who came mostly from Europe, but also from as far afield as China, Japan, Vietnam, Mexico, and Washington State. It is impossible in a short review to cover all the subjects addressed at the meeting, so the following is a personal view of some of the highlights and novel themes to emerge. The workshop got underway with its traditional starting topic of 'Flowering', namely the complex and interconnecting networks used by flowering plants to initiate their reproductive phase in response to numerous environmental and endogenous cues. Much of what is known about flowering comes from the model plant Arabidopsis thaliana, which is a typical annual species that flowers once in its life cycle, promptly sets seed, and dies. It has been known for several years that multiple cues for flowering in Arabidopsis converge on the FLOWERING TIME (FT) protein, which moves from its site of synthesis in the leaves to the shoot apex where flower production is initiated. However, two recent research trends were evident from this year's workshop. First, several mobile signals other than FT are coming to the fore, including a potentially large list of metabolites that can promote flowering, as highlighted in a talk by Reyes Benlloch (IBMCP, Valencia, Spain). Secondly, several research groups are now focusing on alternative models with contrasting life cycles and flowering requirements. For example, the work of George Coupland's laboratory (MPI-Cologne, Germany) demonstrates that endogenous cues that depend on the age of the plant are of particular importance to flowering in perennial Brassicaceae (Hyun et al., 2019). Indeed, although the workshop included a devoted 'evo-devo' session, the prominent presence of new and emerging models (Fig. 1) in all seven scientific sessions meant that evolutionary considerations were discussed throughout the meeting. Many species require vernalization: cold treatment as a necessary prelude to flowering. However, the need for vernalization can cause unwanted delays in plant breeding programs, which is why Richard Immink's group (Wageningen University, The Netherlands) recently made a screen of some 9000 chemical structures to find a compound that could bypass the vernal-ization requirement (Fiers et al., 2017). Two compounds were found to have the desired effect in Arabidopsis, one of which might prove of practical use in crop species. Interestingly, this compound did not appear to act via any of the known dedicated components of the vernalization pathway, but instead induced FT by a novel mechanism, possibly involving the production of hydrogen peroxide. After deciding to flower, a plant must then determine how its flowers should be arranged, and so the workshop turned its attention to the subject of inflorescence architecture. The enlargement of model species from Arabidopsis was clearly apparent in this theme too, with several impressive talks featuring cereals, legumes, Solanaceae, and Asteraceae. One particularly interesting model for inflorescence architecture is cultivated rice, which has undergone the domestication process twice from distinct wild species in Asia and Africa. These domes-tication events appear to have resulted in parallel changes to the rice panicle, and a collaboration involving Stefan Jouannic and Helene Adam (IRD-Montpellier, France) and Ngang Giang Khong (Agricultural Genetic Institute, Hanoi, Vietnam) is taking a multidisciplinary approach to discover whether similar genetic targets and developmental processes wer

High-stringency subtraction for the identification of differentially regulated cDNA clones

The technique of high-stringency subtraction described here facilitates subtractive hybridizations between directional cDNA libraries constructed in ? ZAP® II cloning vectors and represents an improvement on earlier methods for the subtraction of entire cDNA libraries. High-stringency subtraction is designed to eliminate the subtraction of differentially expressed cDNAs, which show similarity to constitutive sequences by the incorporation of a novel high-stringency wash step. This method also allows the size-selection of target cDNAs and incorporates an improved procedure for the synthesis of driver DNA used in subtractions

Current trends and future directions in flower development research

International audienceFlowers, the reproductive structures of the approximately 400 000 extant species of flowering plants, exist in a tremendous range of forms and sizes, mainly due to developmental differences involving the number, arrangement, size and form of the floral organs of which they consist. However, this tremendous diversity is underpinned by a surprisingly robust basic floral structure in which a central group of carpels forms on an axis of determinate growth, almost invariably surrounded by two successive zones containing stamens and perianth organs, respectively. Over the last 25 years, remarkable progress has been achieved in describing the molecular mechanisms that control almost all aspects of flower development, from the phase change that initiates flowering to the final production of fruits and seeds. However, this work has been performed almost exclusively in a small number of eudicot model species, chief among which is Arabidopsis thaliana. Studies of flower development must now be extended to a much wider phylogenetic range of flowering plants and, indeed, to their closest living relatives, the gymnosperms. Studies of further, more wide-ranging models should provide insights that, for various reasons, cannot be obtained by studying the major existing models alone. The use of further models should also help to explain how the first flowering plants evolved from an unknown, although presumably gymnosperm-like ancestor, and rapidly diversified to become the largest major plant group and to dominate the terrestrial flora. The benefits for society of a thorough understanding of flower development are self-evident, as human life depends to a large extent on flowering plants and on the fruits and seeds they produce. In this preface to the Special Issue, we introduce eleven articles on flower development, representing work in both established and further models, including gymnosperms. We also present some of our own views on current trends and future directions of the flower development field

The Men-10 cDNA encodes a novel form of proline-rich protein expressed in the tapetum of dioecious Silene latifolia

The Men-10 gene is expressed specifically in the tapetum tissue that surrounds and nourishes the developing microspores in the dioecious plant species, Silene latifolia. Men-10 encodes a proline-rich protein that contains a predicted signal region, indicating that it may be secreted from the tapetal cells and function in the extracellular domain of the tapetum or be translocated to the developing microspores. Here we report the sequence and precise expression pattern of the Men-10 cDNA and demonstrate a high level of restriction fragment length polymorphism associated with the Men-10 locus. The possible classification of Men-10 amongst known groups of proline- and hydroxyproline-rich glycoproteins, such as the arabinogalactan proteins, is discussed

Carpel evolution in : fruit development an seed dispersal

International audienc

The evolution of plant development : past, present and future

International audienc

Evolution of the ARF Gene Family in Land Plants: Old Domains, New Tricks

International audienceAuxin response factors (ARF) are key players in plant development. They mediate the cellular response to the plant hormone auxin by activating or repressing the expression of downstream developmental genes. The pivotal activation function of ARF proteins is enabled by their four-domain architecture, which includes both DNA-binding and protein dimerization motifs. To determine the evolutionary origin of this characteristic architecture, we built a comprehensive data set of 224 ARF-related protein sequences that represents all major living divisions of land plants, except hornworts. We found that ARFs are split into three subfamilies that could be traced back to the origin of the land plants. We also show that repeated events of extensive gene duplication contributed to the expansion of those three original subfamilies. Further examination of our data set uncovered a broad diversity in the structure of ARF transcripts and allowed us to identify an additional conserved motif in ARF proteins. We found that additional structural diversity in ARF proteins is mainly generated by two mechanisms: genomic truncation and alternative splicing. We propose that the loss of domains from the canonical, four-domain ARF structure has promoted functional shifts within the ARF family by disrupting either dimerization or DNA-binding capabilities. For instance, the loss of dimerization domains in some ARFs from moss and spikemoss genomes leads to proteins that are reminiscent of Aux/IAA proteins, possibly providing a clue on the evolution of these modulators of ARF function. We also assessed the functional impact of alternative splicing in the case of ARF4, for which we have identified a novel isoform in Arabidopsis thaliana. Genetic analysis showed that these two transcripts exhibit markedly different developmental roles in A. thaliana. Gene duplications, domain rearrangement, and post-transcriptional regulation have thus enabled a subtle control of auxin signaling through ARF proteins that may have contributed to the critical importance of these regulators in plant development and evolution

Dioecy in Amborella trichopoda: evidence for genetically based sex determination and its consequences for inferences of the breeding system in early angiosperms

Background and Aims This work aimed to gain insight into the breeding system at the base of living angiosperms through both character state reconstructions and the study of sex ratios and phenotypes in the likely sister to all other living angiosperms, Amborella trichopoda. Methods Sex phenotypes were mapped onto a phylogeny of basally diverging angiosperms using maximum parsimony. In parallel, sex ratios and phenotypes were studied over two consecutive flowering seasons in an ex situ population of A. trichopoda, while the sex ratio of an in situ population was also assessed. Key Results Parsimony analyses failed to resolve the breeding system present at the base of living angiosperms, but indicated the importance of A. trichopoda for the future elucidation of this question. The ex situ A. trichopoda population studied showed a primary sex ratio close to 1:1, though sex ratio bias was found in the in situ population studied. Instances of sexual instability were quantified in both populations. Conclusions Sex ratio data support the presence of genetic sex determination in A. trichopoda, whose further elucidation may guide inferences on the breeding system at the base of living angiosperms. Sexual instability in A. trichopoda suggests the operation of epigenetic mechanisms, and the evolution of dioecy via a gynodioecious intermediate

Laser isolation of plant sex chromosomes:Studies on the DNA composition of the X and Y sex chromosomes of Silene latifolia

X and Y sex chromosomes from the dioecious plant Silene latifolia (white campion) were isolated from mitotic metaphase chromosome preparations on polyester membranes. Autosomes were ablated using an argon ion laser microbeam and isolated sex chromosomes were then recovered on excised fragments of polyester membrane. Sex chromosome associated DNA sequences were amplified using the degenerate oligonucleotide primed polymerase chain reaction (DOP-PCR) and pools of DOP-PCR products were used to investigate the genomic organization of the S. latifolia sex chromosomes. The chromosomal locations of cloned sex chromosome repeat sequences were analysed by fluorescence in situ hybridization and data complementary to laser ablation studies were obtained by genomic in situ hybridization. In combination, these studies demonstrate that the X and Y sex chromosomes of S. latifolia are of very similar DNA composition and also that they share a significant repetitive DNA content with the autosomes. The evolution of sex chromosomes in Silene is discussed and compared with that in another dioecious species, Rumex acetosa

Cloning of PCP1, a member of a family of pollen coat protein (PCP) genes from Brassica oleracea encoding novel cysteine-rich proteins involved in pollen-stigma interactions.

The pollen coatings of both Brassica oleracea and Brassica napus contain a small family of basic 6-8 kDa proteins which are released on to the stigmatic surface on pollination. Following partial amino-acid sequencing of one of these pollen coat proteins (PCPs), PCR primers were constructed to isolate the PCP sequence from anther mRNA using RT-PCR. A cDNA was obtained which, in Northern hybridization experiments, revealed a characteristic pattern of expression during late stages of anther development. Interestingly, in situ hybridization revealed expression of this sequence to be confined to the cytoplasm of the trinucleate pollen grains: no signal was detected in the tapetum. Southern hybridization experiments have shown the gene (PCP1) to be a member of a large family of between 30 and 40 PCP genes in the genome of Brassica oleracea. Surprisingly, RFLP experiments showed reduced copy number (one to two copies) in some of the F2 segregants, perhaps resulting from the clustering of PCP sequences. PCP1 contains a single intron and encodes a small, basic peptide 83 amino acids in length featuring a hydrophobic signal peptide sequence separated from the more hydrophilic, cysteine-rich mature protein. The central part and C-terminal region of the peptide contain a characteristic and invariant pattern of eight cysteines which show clear homology with a number of other anther-specific genes; the remainder of the sequence shows little similarity to other sequences on the data bases. The product of PCP1 is a member of a large family of similar proteins, some of which have been demonstrated to bind specifically to S-locus glycoproteins, but does not appear to be genetically linked to the S-locus