Light-mediated anthocyanin biosynthesis in rose petals involves a balanced regulatory module comprising transcription factors RhHY5, RhMYB114a, and RhMYB3b.

Roses are significant botanical species with both ornamental and economic value, displaying diverse floral traits, particularly an extensive array of petal colors. The red pigmentation of rose petals is predominantly attributed to anthocyanin accumulation. However, the underlying regulatory mechanism of anthocyanin biosynthesis in roses remains elusive. This study presents a novel light-responsive regulatory module governing anthocyanin biosynthesis in rose petals, which involves the transcription factors RhHY5, RhMYB114a, and RhMYB3b. Under light conditions (1000-1500 µmol m-2 s-1), RhHY5 represses RhMYB3b expression and induces RhMYB114a expression, positively regulating anthocyanin biosynthesis in rose petals. Notably, activation of anthocyanin structural genes probably involves an interaction and synergy between RhHY5 and the MYB114a-bHLH3-WD40 complex. Additionally, RhMYB3b is activated by RhMYB114a to prevent excessive accumulation of anthocyanin. Conversely, under low light conditions (<10 µmol m-2 s-1), the degradation of RhHY5 leads to down-regulation of RhMYB114a and up-regulation of RhMYB3b, which in turn inhibits the expression of both RhMYB114a and anthocyanin structural genes. Additionally, RhMYB3b competes with RhMYB114a for binding to RhbHLH3 and the promoters of anthocyanin-related structural genes. Overall, our study uncovers a complex light-mediated regulatory network that governs anthocyanin biosynthesis in rose petals, providing new insights into the molecular mechanisms underlying petal color formation in rose.

Isolation of Staged and Viable Maize Microspores for DH Production.

Isolated microspore culture systems have been designed in maize by several groups, mainly from the late 1980s to early 2000s. However, even with optimized protocols, microspore embryogenesis induction has remained very dependent on the genotype in maize, with elite germplasm generally displaying no response or very low response. Yet, these last few years, significant progress has been accomplished in understanding and controlling microspore embryogenesis induction in model dicot and monocot species. This knowledge may be transferred to maize, and isolated microspore culture may gain new interest in this crop, at least for embryogenesis research. The methods we hereby present in detail permit the purification of 3-12 × 105 viable microspores per maize tassel, at the favorable stage for microspore embryogenesis. When cultured in appropriate liquid media, microspores from responsive genotypes give rise to androgenic embryos, which can then be regenerated into fertile doubled haploid plants.

Crop plants with improved culture and quality traits for food, feed and other uses.

The large French research project GENIUS (2012-2019, https://www6.inra.genius-project_eng/ ) provides a good showcase of current genome editing techniques applied to crop plants. It addresses a large variety of agricultural species (rice, wheat, maize, tomato, potato, oilseed rape, poplar, apple and rose) together with some models (Arabidopsis, Brachypodium, Physcomitrella). Using targeted mutagenesis as its work horse, the project is limited to proof of concept under confined conditions. It mainly covers traits linked to crop culture, such as disease resistance to viruses and fungi, flowering time, plant architecture, tolerance to salinity and plant reproduction but also addresses traits improving the quality of agricultural products for industrial purposes. Examples include virus resistant tomato, early flowering apple and low-amylose starch potato. The wide range of traits illustrates the potential of genome editing towards a more sustainable agriculture through the reduction of pesticides and to the emergence of innovative bio-economy sectors based on custom tailored quality traits.

Biosynthesis of 2-Phenylethanol in Rose Petals Is Linked to the Expression of One Allele of RhPAAS.

Floral scent is one of the most important characters in horticultural plants. Roses (Rosa spp.) have been cultivated for their scent since antiquity. However, probably by selecting for cultivars with long vase life, breeders have lost the fragrant character in many modern roses, especially the ones bred for the cut flower market. The genetic inheritance of scent characters has remained elusive so far. In-depth knowledge of this quantitative trait is thus very much needed to breed more fragrant commercial cultivars. Furthermore, rose hybrids harbor a composite genomic structure, which complexifies quantitative trait studies. To understand rose scent inheritance, we characterized a segregating population from two diploid cultivars, Rosa × hybrida cv H190 and Rosa wichurana, which have contrasting scent profiles. Several quantitative trait loci for the major volatile compounds in this progeny were identified. One among these loci contributing to the production of 2-phenylethanol, responsible for the characteristic odor of rose, was found to be colocalized with a candidate gene belonging to the 2-phenylethanol biosynthesis pathway: the PHENYLACETALDEHYDE SYNTHASE gene RhPAAS An in-depth allele-specific expression analysis in the progeny demonstrated that only one allele was highly expressed and was responsible for the production of 2-phenylethanol. Unexpectedly, its expression was found to start early during flower development, before the production of the volatile 2-phenylethanol, leading to the accumulation of glycosylated compounds in petals.

Independence between friction and velocity distribution in fluids subjected to severe shearing and confinement.

Friction reduction is more than ever a key point in saving natural resources and energy, and the question of how to achieve this concerns first and foremost every lubricated system. Among the observed phenomena related to lubricated friction, limiting shear stress (LSS) appears to be one of the most challenging to explain, since its origin is still uncertain. Various scenarios have been proposed involving a transition to a glassy state under high pressure, shear banding, shear localization, or even the occurrence of slip at the solid-liquid interface, none of which have proven conclusive. This work provides new insights into the mechanisms leading to LSS and the underlying flow organization. It bridges a gap between the scenarios previously discussed in the literature to explain the mechanisms behind LSS and friction experiments, which provide macroscopic results only. We first present some general molecular dynamics (MD) simulations developed to characterize molecular fluids in their bulk state and then proceed to study their response under severe shearing and confinement. Results from simulations are compared to experimental data derived from friction tests. A further analysis of the pressure and temperature involved hints that LSS and the physical state of the lubricant are strongly interconnected concepts. Additionally, the friction results were uncorrelated to the choice of surfaces, contrary to velocity distribution.

The Rosa genome provides new insights into the domestication of modern roses.

Roses have high cultural and economic importance as ornamental plants and in the perfume industry. We report the rose whole-genome sequencing and assembly and resequencing of major genotypes that contributed to rose domestication. We generated a homozygous genotype from a heterozygous diploid modern rose progenitor, Rosa chinensis 'Old Blush'. Using single-molecule real-time sequencing and a meta-assembly approach, we obtained one of the most comprehensive plant genomes to date. Diversity analyses highlighted the mosaic origin of 'La France', one of the first hybrids combining the growth vigor of European species and the recurrent blooming of Chinese species. Genomic segments of Chinese ancestry identified new candidate genes for recurrent blooming. Reconstructing regulatory and secondary metabolism pathways allowed us to propose a model of interconnected regulation of scent and flower color. This genome provides a foundation for understanding the mechanisms governing rose traits and should accelerate improvement in roses, Rosaceae and ornamentals.

Quantum dots to probe temperature and pressure in highly confined liquids.

A new in situ technique for temperature and pressure measurement within dynamic thin-film flows of liquids is presented. The technique is based on the fluorescence emission sensitivity of CdSe/CdS/ZnS quantum dots to temperature and pressure variations. In this respect, the quantum dots were dispersed in squalane, and their emission energy dependence on temperature and pressure was calibrated under static conditions. Temperature calibration was established between 295 K and 393 K showing a temperature sensitivity of 0.32 meV K-1. Pressure calibration was, in turn, conducted up to 1.1 GPa using a diamond anvil cell, yielding a pressure sensitivity of 33.2 meV GPa-1. The potential of CdSe/CdS/ZnS quantum dots as sensors to probe temperature and pressure was proven by applying the in situ technique to thin films of liquids undergoing dynamic conditions. Namely, temperature rises have been measured in liquid films subjected to shear heating between two parallel plates in an optical rheometer. In addition, pressure rises have been measured in a lubricated point contact under pure rolling and isothermal conditions. In both cases, the measured values have been successfully compared with theoretical or numerical predictions. These comparisons allowed the validation of the new in situ technique and demonstrated the potential of the quantum dots for further mapping application in more complex and/or severe conditions.

Nanolubrication by ionic liquids: molecular dynamics simulations reveal an anomalous effective rheology.

This article describes molecular dynamics simulations of an ionic liquid (IL) confined between iron oxide surfaces under relatively high pressure and severe shearing, representative of a typical steel-steel lubricated contact. The simulations reveal the presence of hydrodynamic and thermal slip at the walls, despite the wetting nature of the fluid/wall interface. A crucial consequence of the temperature slip is the subsequent increase of the fluid temperature under shear, which modifies its effective rheology, resulting in saturation of the shear stress at high shear rates. Overall, this article provides a methodology for accurate modeling of tribological contacts lubricated by a nanometer-thick IL film. The results contribute to the debate on the saturation of the shear stress at high shear rates, and reveal the rich phenomenology arising in severe tribological conditions, departing from the traditional understanding of nanofluidic transport, mainly built in the linear response regime and standard thermodynamic conditions.

PLANT VOLATILES. Biosynthesis of monoterpene scent compounds in roses.

The scent of roses (Rosa x hybrida) is composed of hundreds of volatile molecules. Monoterpenes represent up to 70% percent of the scent content in some cultivars, such as the Papa Meilland rose. Monoterpene biosynthesis in plants relies on plastid-localized terpene synthases. Combining transcriptomic and genetic approaches, we show that the Nudix hydrolase RhNUDX1, localized in the cytoplasm, is part of a pathway for the biosynthesis of free monoterpene alcohols that contribute to fragrance in roses. The RhNUDX1 protein shows geranyl diphosphate diphosphohydrolase activity in vitro and supports geraniol biosynthesis in planta.

Luminescence nanothermometry with alkyl-capped silicon nanoparticles dispersed in nonpolar liquids.

Silicon nanoparticles (Si NPs) with a diameter size ranging from 4 to 8 nm were successfully fabricated. They exhibit a visible photoluminescence (PL) due to the quantum confinement effect. Chemical functionalization of these Si NPs with alkyl groups allowed to homogeneously disperse them in nonpolar liquids (NPLs). In comparison to most of literature results for Si NPs, an important PL peak position variation with temperature (almost 1 meV/K) was obtained from 303 to 390 K. The influence of the liquid viscosity on the peak positions is also presented. These variations are discussed considering energy transfer between nanoparticles. The high PL thermal sensitivity of the alkyl-capped Si NPs paves the way for their future application as nanothermometers.

Genomic approach to study floral development genes in Rosa sp.

Cultivated for centuries, the varieties of rose have been selected based on a number of flower traits. Understanding the genetic and molecular basis that contributes to these traits will impact on future improvements for this economically important ornamental plant. In this study, we used scanning electron microscopy and sections of meristems and flowers to establish a precise morphological calendar from early rose flower development stages to senescing flowers. Global gene expression was investigated from floral meristem initiation up to flower senescence in three rose genotypes exhibiting contrasted floral traits including continuous versus once flowering and simple versus double flower architecture, using a newly developed Affymetrix microarray (Rosa1_Affyarray) tool containing sequences representing 4765 unigenes expressed during flower development. Data analyses permitted the identification of genes associated with floral transition, floral organs initiation up to flower senescence. Quantitative real time PCR analyses validated the mRNA accumulation changes observed in microarray hybridizations for a selection of 24 genes expressed at either high or low levels. Our data describe the early flower development stages in Rosa sp, the production of a rose microarray and demonstrate its usefulness and reliability to study gene expression during extensive development phases, from the vegetative meristem to the senescent flower.

Energy dissipation in non-isothermal molecular dynamics simulations of confined liquids under shear.

Energy is commonly dissipated in molecular dynamics simulations by using a thermostat. In non-isothermal shear simulations of confined liquids, the choice of the thermostat is very delicate. We show in this paper that under certain conditions, the use of classical thermostats can lead to an erroneous description of the dynamics in the confined system. This occurs when a critical shear rate is surpassed as the thermo-viscous effects become prominent. In this high-shear-high-dissipation regime, advanced dissipation methods including a novel one are introduced and compared. The MD results show that the physical modeling of both the accommodation of the surface temperature to liquid heating and the heat conduction through the confining solids is essential. The novel method offers several advantages on existing ones including computational efficiency and easiness of application for complex systems.

Tinkering with the C-function: a molecular frame for the selection of double flowers in cultivated roses.

BACKGROUND: Roses have been cultivated for centuries and a number of varieties have been selected based on flower traits such as petal form, color, and number. Wild-type roses have five petals (simple flowers), whereas high numbers of petals (double flowers) are typical attributes of most of the cultivated roses. Here, we investigated the molecular mechanisms that could have been selected to control petal number in roses. METHODOLOGY/PRINCIPAL FINDINGS: We have analyzed the expression of several candidate genes known to be involved in floral organ identity determination in roses from similar genetic backgrounds but exhibiting contrasting petal numbers per flower. We show that the rose ortholog of AGAMOUS (RhAG) is differentially expressed in double flowers as compared to simple flowers. In situ hybridization experiments confirm the differential expression of RhAG and demonstrate that in the double-flower roses, the expression domain of RhAG is restricted toward the center of the flower. Conversely, in simple-flower roses, RhAG expression domain is wider. We further show that the border of RhAG expression domain is labile, which allows the selection of rose flowers with increased petal number. Double-flower roses were selected independently in the two major regions for domestication, China and the peri-Mediterranean areas. Comparison of RhAG expression in the wild-type ancestors of cultivated roses and their descendants both in the European and Chinese lineages corroborates the correlation between the degree of restriction of RhAG expression domain and the number of petals. Our data suggests that a restriction of RhAG expression domain is the basis for selection of double flowers in both the Chinese and peri-Mediterranean centers of domestication. CONCLUSIONS/SIGNIFICANCE: We demonstrate that a shift in RhAG expression domain boundary occurred in rose hybrids, causing double-flower phenotype. This molecular event was selected independently during rose domestication in Europe/Middle East and in China.

Role of petal-specific orcinol O-methyltransferases in the evolution of rose scent.

Orcinol O-methyltransferase (OOMT) 1 and 2 catalyze the last two steps of the biosynthetic pathway leading to the phenolic methyl ether 3,5-dimethoxytoluene (DMT), the major scent compound of many rose (Rosa x hybrida) varieties. Modern roses are descended from both European and Chinese species, the latter being producers of phenolic methyl ethers but not the former. Here we investigated why phenolic methyl ether production occurs in some but not all rose varieties. In DMT-producing varieties, OOMTs were shown to be localized specifically in the petal, predominantly in the adaxial epidermal cells. In these cells, OOMTs become increasingly associated with membranes during petal development, suggesting that the scent biosynthesis pathway catalyzed by these enzymes may be directly linked to the cells' secretory machinery. OOMT gene sequences were detected in two non-DMT-producing rose species of European origin, but no mRNA transcripts were detected, and these varieties lacked both OOMT protein and enzyme activity. These data indicate that up-regulation of OOMT gene expression may have been a critical step in the evolution of scent production in roses.

Biosynthesis of the major scent components 3,5-dimethoxytoluene and 1,3,5-trimethoxybenzene by novel rose O-methyltransferases.

In Chinese rose species and in many modern varieties, two methylated phenolic derivatives, 3,5-dimethoxytoluene and 1,3,5-trimethoxybenzene, are major scent components. We show that cell-free extracts of rose petals catalyse the synthesis of 3,5-dimethoxytoluene and 1,3,5-trimethoxybenzene by methylation of precursor molecules. An expressed sequence tag approach was used to identify four highly similar O-methyltransferase sequences expressed specifically in petals and anthers. Thin layer chromatography analysis showed that the activities of these enzymes with different substrates and the proportions of reaction products produced closely mimicked those observed using cell-free petal extracts, indicating that orcinol O-methyltransferases are responsible for the biosynthesis of 3,5-dimethoxytoluene and 1,3,5-trimethoxybenzene from un-methylated precursors in this organ.

Analysis of gene expression in rose petals using expressed sequence tags.

Single-pass sequences were obtained from the 5'-ends of a total of 1794 rose petal cDNA clones. Cluster analysis identified 242 groups of sequences and 635 singletons indicating that the database represents a total of 877 genes. Putative functions could be assigned to 1151 of the transcripts. Expression analysis indicated that transcripts of several of the genes identified accumulated specifically in petals and stamens. The cDNA library and expressed sequence tag database described here represent a valuable resource for future research aimed at improving economically important rose characteristics such as flower form, longevity and scent.