The wild side of grape genomics.

With broad genetic diversity and as a source of key agronomic traits, wild grape species (Vitis spp.) are crucial to enhance viticulture's climatic resilience and sustainability. This review discusses how recent breakthroughs in the genome assembly and analysis of wild grape species have led to discoveries on grape evolution, from wild species' adaptation to environmental stress to grape domestication. We detail how diploid chromosome-scale genomes from wild Vitis spp. have enabled the identification of candidate disease-resistance and flower sex determination genes and the creation of the first Vitis graph-based pangenome. Finally, we explore how wild grape genomics can impact grape research and viticulture, including aspects such as data sharing, the development of functional genomics tools, and the acceleration of genetic improvement.

Multiple independent recombinations led to hermaphroditism in grapevine.

Hermaphroditic (perfect) flowers were a key trait in grapevine domestication, enabling a drastic increase in yields due to the efficiency of self-pollination in the domesticated grapevine (Vitis vinifera L. ssp. vinifera). In contrast, all extant wild Vitis species are dioecious, each plant having only male or female flowers. In this study, we identified the male (M) and female (f) haplotypes of the sex-determining region (SDR) in the wild grapevine species V. cinerea and confirmed the boundaries of the SDR. We also demonstrated that the SDR and its boundaries are precisely conserved across the Vitis genus using shotgun resequencing data of 556 wild and domesticated accessions from North America, East Asia, and Europe. A high linkage disequilibrium was found at the SDR in all wild grape species, while different recombination signatures were observed along the hermaphrodite (H) haplotype of 363 cultivated accessions, revealing two distinct H haplotypes, named H1 and H2. To further examine the H2 haplotype, we sequenced the genome of two grapevine cultivars, 'Riesling' and 'Chardonnay'. By reconstructing the first two H2 haplotypes, we estimated the divergence time between H1 and H2 haplotypes at ∼6 million years ago, which predates the domestication of grapevine (∼8,000 y ago). Our findings emphasize the important role of recombination suppression in maintaining dioecy in wild grape species and lend additional support to the hypothesis that at least two independent recombination events led to the reversion to hermaphroditism in grapevine.

Comparative RNA-Seq analysis reveals genes associated with masculinization in female Cannabis sativa.

MAIN CONCLUSION: Using RNA profiling, we identified several silver thiosulfate-induced genes that potentially control the masculinization of female Cannabis sativa plants. Genetically female Cannabis sativa plants normally bear female flowers, but can develop male flowers in response to environmental and developmental cues. In an attempt to elucidate the molecular elements responsible for sex expression in C. sativa plants, we developed genetically female lines producing both female and chemically-induced male flowers. Furthermore, we carried out RNA-Seq assays aimed at identifying differentially expressed genes responsible for male flower development in female plants. The results revealed over 10,500 differentially expressed genes, of which around 200 potentially control masculinization of female cannabis plants. These genes include transcription factors and other genes involved in male organ (i.e., anther and pollen) development, as well as genes involved in phytohormone signalling and male-biased phenotypes. The expressions of 15 of these genes were further validated by qPCR assay confirming similar expression patterns to that of RNA-Seq data. These genes would be useful for understanding predisposed plants producing flowers of both sex types in the same plant, and help breeders to regulate the masculinization of female plants through targeted breeding and plant biotechnology.

Unusual positional effects on flower sex in an andromonoecious tree: Resource competition, architectural constraints, or inhibition by the apical flower?

PREMISE OF THE STUDY: Two, nonmutually exclusive, mechanisms-competition for resources and architectural constraints-have been proposed to explain the proximal to distal decline in flower size, mass, and/or femaleness in indeterminate, elongate inflorescences. Whether these mechanisms also explain unusual positional effects such as distal to proximal declines of floral performance in determinate inflorescences, is understudied. METHODS: We tested the relative influence of these mechanisms in the andromonoecious wild olive tree, where hermaphroditic flowers occur mainly on apical and the most proximal positions in determinate inflorescences. We experimentally increased the availability of resources for the inflorescences by removing half of the inflorescences per twig or reduced resource availability by removing leaves. We also removed the apical flower to test its inhibitory effect on subapical flowers. KEY RESULTS: The apical flower had the highest probability of being hermaphroditic. Further down, however, the probability of finding a hermaphroditic flower decreased from the base to the tip of the inflorescences. An experimental increase of resources increased the probability of finding hermaphroditic flowers at each position, and vice versa. Removal of the apical flower increased the probability of producing hermaphroditic flowers in proximal positions but not in subapical positions. CONCLUSIONS: These results indicate an interaction between resource competition and architectural constraints in influencing the arrangement of the hermaphroditic and male flowers within the inflorescences of the wild olive tree. Subapical flowers did not seem to be hormonally suppressed by apical flowers. The study of these unusual positional effects is needed for a general understanding about the functional implications of inflorescence architecture.

Darwin's inflorescence syndrome is indeed associated with bee pollination.

KEY MESSAGE: A relationship between vertical acropetal inflorescences with protandrous flowers and bee pollination was hypothesized by Darwin back in 1877. Here we provide empirical evidence supporting this association across the angiosperms. Plant reproduction is not only determined by flower traits but also by the arrangement of flowers within inflorescences. Based on his observations of the orchid Spiranthes autumnalis, Darwin proposed in 1877 that bee-pollinated plants presenting protandrous flowers on vertical acropetal inflorescences, where proximal flowers open first, can exploit the stereotypical foraging behavior of their pollinators (i.e., upward movement through the inflorescence) to promote pollen exportation and reduce self-pollination. In these inflorescences, male-phase flowers lie spatially above female-phase flowers. To examine this untested hypothesis, we compiled literature information from 718 angiosperms species and evaluated the association between vertical acropetal inflorescences with protandrous flowers and bee pollination within a phylogenetic comparative framework. Results reveal that this type of inflorescence is indeed more common in species pollinated by bees. Moreover, this association does not seem to be weakened by the presence of alternative self-pollination avoidance mechanisms, like self-incompatibility, suggesting that this inflorescence type benefits mainly male rather than female fitness. Other inflorescence types placing male-phase flowers above female-phase flowers, e.g., vertical basipetal inflorescences with protogynous flowers, do not provide strong evidence of a differential association with pollination by bees. Female-biased nectar production in vertical acropetal inflorescences with protandrous flowers may reinforce the behavior of bees to fly upwards, rendering Darwin's configuration more adaptive than other inflorescence configurations.

Flower heterochrony and crop yield.

Crop improvement has focused on enhancing yield, nutrient content, harvestability, and stress resistance using a trait-centered reductionist approach. This has downplayed the fact that plants are developmentally integrated and respond coordinately and predictably to genetic and environmental variation, with potential consequences for food production. Crop yield, including both fruit/seed production and the possibility of generating hybrid crop varieties, is highly dependent on flower morphology and sex, which, in turn, can be profoundly affected by slight shifts in the timing and rate of flower organ development (i.e., flower heterochrony). We argue that understanding the genetic and environmental bases of flower heterochrony and their effect on flower morphology and sex in cultivated plants and in their wild relatives can facilitate crop improvement.

Floral Characterization of Pomegranate Genotypes to Improve Hybridization Efficiency.

Pomegranate (Punica granatum) has staminate (male), androgynous (hermaphrodite), and intermediate flower types. Floral characterization is difficult for breeding efficiency across many pomegranate genotypes in Pakistan, which is essential for pomegranate cultivar enhancements. The present research focused on the floral characterization and breeding efficiency of fifteen pomegranate genotypes. Flower sex ratio, floral morphological parameters, i.e., flower length, ovary width, flower notch, flower tip and stigma with style length, and fruit set percentage were examined during the experiment. In terms of sex ratio, male flowers were found to be higher among all genotypes. Due to clear differences in flower length, width, and heterostyly facilitating visual identification of the hermaphrodite flowers, genotype Ternab-2, Kandhari White, and Kandhari Red had higher fruit set (≥70%) among all cross combinations attempted. Genotype Sava had higher flower length and heterostyly of hermaphrodite flower type, but ovary width was not very distinct, leading to average crossing success (85-34%). In conclusion, single or combination of morphological characters can be used for accurate identification of hermaphrodite flowers, which can improve hybrid efficiency and fruit set after artificial cross-pollination.

Visita de abejas (Apis mellifera, Hymenoptera: Apoidea) a flores de melón Cucumis melo (Cucurvitaceae) en Panamá

Bee (Apis mellifera, Hymenoptera: Apoidea) visitation to cantaloupe Cucumis melo (Cucurvitaceae) flowers in Panama. Flower visits by bees were observed in a melon cultivated field of San Lorenzo district, in Chiriquí, Panama, from January 6 to February 19, 2002, from 6:30 am to 4:30 pm We recorded the duration of each foraging event and the type of resource collected. Flower visits were mostly for nectar collection (∼75 %). Pollen foraging was concentrated in the first hours of the morning and ended by 11:00 am The mean collection time was similar for both food resources, but was different between flower sexes. Flower visits to female flowers took longer (Student's t test, p<0.0001), with a mean time duration of 8.4±4.4 s, whereas in male flowers mean visitation time was of 4.0±1.5 s. Finally, the mean time for each floral sex remained practically constant through the evolution of the crop. Our results were similar to the found ones in temperate zone crops, so apparently tropical conditions of Panama do not change the bee visit patterns on melon flowers. Rev. Biol. Trop. 55 (2): 677-680. Epub 2007 June, 29.

Se observaron las visitas observadas a flores seleccionadas en un cultivo del Distrito de San Lorenzo, Chiriquí, del 6 de Enero y el 19 de Febrero del 2002, desde las 6:30 am hasta las 4:30 pm, y se anotaron características de las visita, como el tiempo de visita y el tipo de recurso colectado. Las visitas fueron mayormente para la recolección de néctar (casi 3/4). La recolección de polen se concentró hacia las primeras horas de la mañana, cesando definitivamente a las 11:00 am. El tiempo medio de recolección fue similar para ambos recursos, pero fue marcadamente distinto para cada sexo floral. Las visitas a flores femeninas fueron significativamente (Prueba t Student, p<0.0001) más largas, con un tiempo medio de duración de 8.4±4.4 s, mientras que en las flores masculinas, el tiempo medio de visita fue 4.0±1.5 s. Por último, el tiempo medio de recolección por sexo floral permaneció prácticamente constante conforme evolucionó el cultivo. Nuestros resultados fueron similares a los encontrados en cultivos de zonas templadas, por lo que aparentemente las condiciones tropicales de Panamá no cambian los patrones de visita que presentan las abejas en las flores de melón.