The hormone regulatory mechanism underlying parthenocarpic fruit formation in tomato.

Parthenocarpic fruits, known for their superior taste and reliable yields in adverse conditions, develop without the need for fertilization or pollination. Exploring the physiological and molecular mechanisms behind parthenocarpic fruit development holds both theoretical and practical significance, making it a crucial area of study. This review examines how plant hormones and MADS-box transcription factors control parthenocarpic fruit formation. It delves into various aspects of plant hormones-including auxin, gibberellic acid, cytokinins, ethylene, and abscisic acid-ranging from external application to biosynthesis, metabolism, signaling pathways, and their interplay in influencing parthenocarpic fruit development. The review also explores the involvement of MADS family gene functions in these processes. Lastly, we highlight existing knowledge gaps and propose directions for future research on parthenocarpy.

Parthenocarpy, a pollination-independent fruit set mechanism to ensure yield stability.

Fruit development is essential for flowering plants' reproduction and a significant food source. Climate change threatens fruit yields due to its impact on pollination and fertilization processes, especially vulnerable to extreme temperatures, insufficient light, and pollinator decline. Parthenocarpy, the development of fruit without fertilization, offers a solution, ensuring yield stability in adverse conditions and enhancing fruit quality. Parthenocarpic fruits not only secure agricultural production but also exhibit improved texture, appearance, and shelf life, making them desirable for food processing and other applications. Recent research unveils the molecular mechanisms behind parthenocarpy, implicating transcription factors (TFs), noncoding RNAs, and phytohormones such as auxin, gibberellin (GA), and cytokinin (CK). Here we review recent findings, construct regulatory models, and identify areas for further research.

New population of Solanum pimpinellifolium backcross inbred lines as a resource for heat stress tolerance in tomato.

The occurring temperature increase in crop production areas worldwide is generating conditions of heat stress that negatively affect crop productivity. Tomato (Solanum lycopersicum), a major vegetable crop, is highly susceptible to elevated temperatures. Under such conditions, fruit set is dramatically reduced, leading to significant yield losses. Solanum pimpinellifolium, a wild species closely related to the cultivated tomato, was shown to have beneficial attributes under various abiotic stress growth conditions. We have utilized a new population of backcross inbred lines originated from a cross between S. pimpinellifolium and S. lycopersicum, in order to evaluate its potential as a new genetic resource for improvement of reproductive performance of cultivated tomato under heat stress conditions. This population was screened for various heat stress-related traits, under controlled heat stress and non-stress conditions. Our results show that significant variation exists for all the heat stress related traits that were examined and point at individual lines with better reproductive performance under heat stress conditions that share a common introgression from the wild S. pimpinellifolium parent, suggesting several candidate genes as potential drivers of thermotolerance. Thus, our results place this population as a valuable new resource for the discovery of heat stress related genetic loci for the future development of heat stress tolerant tomato cultivars.

Anthropogenic land-use change decreases pollination and male and female fitness in terrestrial flowering plants.

BACKGROUND AND AIMS: The majority of the earth's land area is currently occupied by humans. Measuring how terrestrial plants reproduce in these pervasive environments is essential for understanding their long-term viability and their ability to adapt to changing environments. METHODS: We conducted hierarchical and phylogenetically-independent meta-analyses to assess the overall effects of anthropogenic land-use changes on pollination, and male and female fitness in terrestrial plants. KEY RESULTS: We found negative global effects of land use change (i.e., mainly habitat loss and fragmentation) on pollination and on female and male fitness of terrestrial flowering plants. Negative effects were stronger in plants with self-incompatibility (SI) systems and pollinated by invertebrates, regardless of life form and sexual expression. Pollination and female fitness of pollination generalist and specialist plants were similarly negatively affected by land-use change, whereas male fitness of specialist plants showed no effects. CONCLUSIONS: Our findings indicate that angiosperm populations remaining in fragmented habitats negatively affect pollination, and female and male fitness, which will likely decrease the recruitment, survival, and long-term viability of plant populations remaining in fragmented landscapes. We underline the main current gaps of knowledge for future research agendas and call out not only for a decrease in the current rates of land-use changes across the world but also to embark on active restoration efforts to increase the area and connectivity of remaining natural habitats.

ERECTA Modulates Seed Germination and Fruit Development via Auxin Signaling in Tomato.

Tomato (Solanum lycopersicum) breeding for improved fruit quality emphasizes selecting for desirable taste and characteristics, as well as enhancing disease resistance and yield. Seed germination is the initial step in the plant life cycle and directly affects crop productivity and yield. ERECTA (ER) is a receptor-like kinase (RLK) family protein known for its involvement in diverse developmental processes. We characterized a Micro-Tom EMS mutant designated as a knock-out mutant of sler. Our research reveals that SlER plays a central role in controlling critical traits such as inflorescence development, seed number, and seed germination. The elevation in auxin levels and alterations in the expression of ABSCISIC ACID INSENSITIVE 3 (ABI3) and ABI5 in sler seeds compared to the WT indicate that SlER modulates seed germination via auxin and abscisic acid (ABA) signaling. Additionally, we detected an increase in auxin content in the sler ovary and changes in the expression of auxin synthesis genes YUCCA flavin monooxygenases 1 (YUC1), YUC4, YUC5, and YUC6 as well as auxin response genes AUXIN RESPONSE FACTOR 5 (ARF5) and ARF7, suggesting that SlER regulates fruit development via auxin signaling.

Genetic and molecular mechanisms underlying the parthenocarpic fruit mutation in tomato.

Parthenocarpy allows fruit set independently of fertilization. In parthenocarpic-prone tomato genotypes, fruit set can be achieved under pollen-limiting environmental conditions and in sterile mutants. Parthenocarpy is also regarded as a quality-related trait, when seedlessness is associated with positive fruit quality aspects. Among the different sources of genetic parthenocarpy described in tomato, the parthenocarpic fruit (pat) mutation is of particular interest because of its strong expressivity, high fruit set, and enhanced fruit quality. The complexity of the pat "syndrome" associates a strong competence for parthenocarpy with a complex floral phenotype involving stamen and ovule developmental aberrations. To understand the genetic basis of the phenotype, we mapped the pat locus within a 0.19-cM window of Chr3, comprising nine coding loci. A non-tolerated missense mutation found in the 14th exon of Solyc03g120910, the tomato ortholog of the Arabidopsis HD-Zip III transcription factor HB15 (SlHB15), cosegregated with the pat phenotype. The role of SlHB15 in tomato reproductive development was supported by its expression in developing ovules. The link between pat and SlHB15 was validated by complementation and knock out experiments by co-suppression and CRISPR/Cas9 approaches. Comparing the phenotypes of pat and those of Arabidopsis HB15 mutants, we argued that the gene plays similar functions in species with fleshy and dry fruits, supporting a conserved mechanism of fruit set regulation in plants.

What are the drivers of female success in food-deceptive orchids?

A large suite of floral signals, and environmental and biotic characteristics influence the behavior of pollinators, affecting the female success of food-deceptive orchids. In this study, we examined the many factors shaping the reproductive output of three orchid taxa: Dactylorhiza majalis, D. incarnata var. incarnata, and D. fuchsii. We applied a statistical model to correlate female success (number of fruit sets) with individual characteristics (plant and inflorescence height, number of flowers, and spur length), number of pollinaria removed, flowering time, and density of floral units of co-flowering rewarding plants. Our findings suggested that the broad spectrum of variations in Dactylorhiza's morphological traits, floral display, and flowering phenology within different environmental contexts has a significant impact on their reproductive success. The number of fruits increased with an increase in the number of pollinaria removed in the studied Dactylorhiza taxa. In contrast, a higher number of flowers per inflorescence and higher inflorescences in relation to individual height always decreased fruit set. We observed that low number of co-flowering rewarding plants in populations could affect the Dactylorhiza reproductive output as magnets and competitor plants. The synchronization of flowering, or lack thereof, between Dactylorhiza and rewarding plants can limit reproductive success. This demonstrates that the food deception strategy is multidirectional, and reproductive output can vary considerably both spatially and temporally within the context of this strategy.

The patterns of inbreeding depression in food-deceptive Dactylorhiza orchids.

Introduction: Inbreeding depression (ID) in food-deceptive plants have been reported previously, however, it has not been often proven that selfed seeds germinate better than outbred ones or that selfing affects ID. To resolved these issues, food-deceptive related Dactylorhiza majalis, D. incarnata var. incarnata and D. fuchsii orchids were investigated. Methods: Hand pollination treatments and control pollination were conducted. Fruit set, number of seeds per fruit, seed length, number of well-developed seeds per fruit, and proportion of in vitro asymbiotic germination seeds, were analyzed in relation to inflorescence levels and used as fitness indicators for these orchids. The ID and pollen limitation were measured. Results: The lowest ID (δ = -1.000) was in D. majalis, and present in combination with a high pollen limitation in its populations. D. fuchsii showed higher ID (δ = 0.366), and D. incarnata var. incarnata weak ID (δ = 0.065), although ID varied between its fitness components. The seed number per fruit differed significantly between the treatments and the inflorescence levels in treatments. Discussion: This study emphasizes that the breeding system rather than the flower position on the inflorescence shaped the quality and quantity of reproductive output. The ID and its effect on germination of food-deceptive orchid seeds undoubtedly played an important role.

Olive reproductive biology: implications for yield, compatibility conundrum, and environmental constraints.

Olive (Olea europaea L.) is an important Mediterranean tree species with a longstanding history of cultivation, boasting a diverse array of local cultivars. While traditional olive orchards are valued for their cultural and aesthetic significance, they often face economic sustainability challenges in the modern context. The success of both traditional and newly introduced cultivars (e.g. those obtained by cross-breeding) is hindered by self-incompatibility, a prevalent issue for this species that results in low fruit set when limited genetic diversity is present. Further, biological, environmental, and agronomic factors have been shown to interlink in shaping fertilization patterns, hence impacting on the final yield. Climatic conditions during pollination, such as excessive rainfall or high temperatures, can further exacerbate the problem. In this work, we provide an overview of the various factors that trigger the phenomenon of suboptimal fruit set in olive trees. This work provides a comprehensive understanding of the interplay among these factors, shedding light on potential mechanisms and pathways that contribute to the observed outcomes in the context of self-incompatibility in olive.

Plant Reproductive Success Mediated by Nectar Offered to Pollinators and Defensive Ants in Terrestrial Bromeliaceae.

Most plants produce floral nectar to attract pollinators that impact pollination and seed production; some of them also secrete extrafloral nectar harvested by insects that may influence the plant reproductive success. The aim of this study was to analyze the effects of excluding pollinators and/or ants on the per-plant reproductive success in two species (Dyckia floribunda Griseb. and Dyckia longipetala Baker, Bromeliaceae) that produce floral and extrafloral nectar. The hypothesis states that both ecological processes (pollination and ant defense) involving nectar-mediated animal-plant interactions are beneficial for plant reproductive success. We expected the highest decrease in the plant fruit and seed sets when the pollinators and ants were excluded, and a moderate decrease when solely ants were excluded, compared to the control plants (those exposed to pollinators and ants). In addition, a lower natural reproductive success was also expected in the self-incompatible D. longipetala than in the self-compatible D. floribunda, as the former totally depends on animal pollination for seed production. D. floribunda and D. longipetala presented similar trends in the response variables, and the expected results for the experimental treatments were observed, with some variations between species and among populations. The ecological function of nectar is important because these two plant species depend on pollinators to produce seeds and on ants to defend flowers from the endophytic larvae of Lepidoptera. The study of multispecies interactions through mechanistic experiments could be necessary to clarify the specific effects of different animals on plant reproductive success.

Vertebrates can be more important pollinators than invertebrates on islands: the case of Malva (=Lavatera) arborea L.

Premise of the study: On islands, flowering plants tend to be more generalist in their pollination needs, as insects (the main pollinators of flowering plants) are underrepresented in these ecosystems compared to the mainland. In addition, some vertebrate species that are typically insectivorous or granivorous on the mainland are forced to broaden their diet and consume other resources such as nectar or pollen on the islands. The shrub Malva arborea, with its large and colourful flowers, attracts different groups of potential pollinators. This study aimed to compare the effectiveness of vertebrates versus insects in an insular population of M. arborea and to investigate its reproductive system. Methods: For three groups of taxa (insects, birds and lizards), we assessed the two components of pollination effectiveness: (i) the quantitative component (i.e. number of visits and number of flowers contacted) through direct observations of flowers; and (ii) the qualitative component (fruit and seed set, number and size of seeds and proportion of seedling emergence) through pollinator exclusion experiments. Key results: Vertebrates (birds and lizards) were quantitatively the most effective pollinators, followed by insects. However, when all three groups visited the flowers, fruit and seed set were higher than when any of them were excluded. We also found that M. arborea has hermaphrodite flowers and is able to reproduce by autogamy, although less efficiently than when pollinated by animals. Conclusions: Both vertebrates and insects play an important role in the reproduction of M. arborea. Although the plant does not need pollinators to produce seeds, its reproductive success increases when all pollinators are allowed to visit the flowers. Besides providing new information on M. arborea, these findings may help to better understand the role of different pollinator groups in the reproduction of other plant species, especially on islands where the co-occurrence of vertebrate and invertebrate pollination in the same plant species is usual.

New Advances in the Study of Regulation of Tomato Flowering-Related Genes Using Biotechnological Approaches.

The tomato is a convenient object for studying reproductive processes, which has become a classic. Such complex processes as flowering and fruit setting require an understanding of the fundamental principles of molecular interaction, the structures of genes and proteins, the construction of signaling pathways for transcription regulation, including the synchronous actions of cis-regulatory elements (promoter and enhancer), trans-regulatory elements (transcription factors and regulatory RNAs), and transposable elements and epigenetic regulators (DNA methylation and acetylation, chromatin structure). Here, we discuss the current state of research on tomatoes (2017-2023) devoted to studying the function of genes that regulate flowering and signal regulation systems using genome-editing technologies, RNA interference gene silencing, and gene overexpression, including heterologous expression. Although the central candidate genes for these regulatory components have been identified, a complete picture of their relationship has yet to be formed. Therefore, this review summarizes the latest achievements related to studying the processes of flowering and fruit set. This work attempts to display the gene interaction scheme to better understand the events under consideration.

Mating strategies of Vitex negundo L. var. heterophylla (Franch.) Rehder (Lamiaceae): A mixed mating system with inbreeding depression.

Plant reproductive ecology is one of the research hotspots in ecology. With the increasing attention paid to the conservation of plant diversity, the research on reproductive characteristics and flowering biological characteristics of more species has attracted more attention. However, plant reproduction is affected by multiple interacting factors such as pollen limitation and resource availability. Vitex negundo var. heterophylla (Franch.) Rehder (Lamiaceae) is a significant species for water and soil conservation. Previous studies have revealed its mating system by the biological characteristics of flowering and SSR markers, but its reproductive strategies remain to be further studied. We evaluated reproductive success through artificial pollination to explore the reproductive characteristics of V. negundo var. heterophylla for the first time. From the results of fruit set, there is a mixed mating system dominated by outcrossing in V. negundo var. heterophylla accompanied by self-compatibility, and it cannot carry out autonomous selfing. Our data show the pollinator-mediated interaction in the success of reproduction, whereas the effect of anemophily is very weak. And the seed germination rate of inbred line progenies was lower than that of hybrid progenies, which is suspected to be caused by inbreeding depression. The research will provide scientific information for the protection and conservation of V. negundo var. heterophylla from the point of view of reproduction. In sum, the results are necessary to protect animal vectors in the background of insect decline.

Gametophytic self-incompatibility in Maxillariinae orchids.

Gametophytic self-incompatibility (GSI) has been mainly described in species-rich clades within Orchidaceae. We report GSI for a genus within Maxillariinae, one of the most conspicuous and diverse subtribes of neotropical orchids. Here, we describe the reproductive system of Brasiliorchis picta, B. phoenicanthera, and B. porphyrostele. Anatomical studies of fruit development showed that pollen tubes of aborted, self-pollinated flowers degenerate half-way in the stylar channel and never reach the ovules. Spontaneous self-pollination and emasculation set no fruits for none of the sampled species, thus supporting the hypothesis that these three species studied rely on the agency of pollinators and pollinator-mediated cross-pollination to set fruit. Fruit set from cross-pollinations ranged from 33.4 to 77.5%. One self-pollinated fruit of B. porphyrostele developed to completion. All other fruits aborted between 10 and 21 days after pollination. These data support previous evidence of variable strength GSI being exhibited in orchid species. Additional studies of self-incompatibility systems are needed to evaluate their role in species diversification and evolution of reproductive strategies in Maxillariinae and to allow for effective conservation strategies of threatened orchid species.

From flower to fruit: fruit growth and development in olive (Olea europaea L.)-a review.

The olive (Olea europaea L.) is the most cultivated tree crop in the Mediterranean and among the most cultivated tree crops worldwide. Olive yield is obtained by the product of fruit number and fruit size; therefore, understanding fruit development, in terms of both number and size, is commercially and scientifically relevant. This article reviews the literature on fruit development, from the flower to the mature fruit, considering factors that affect both fruit size and number. The review focuses on olive but includes literature on other species when relevant. The review brings the different factors affecting different phases of fruit development, addressed separately in the literature, under a single frame of interpretation. It is concluded that the different mechanisms regulating the different phases of fruit development, from pistil abortion to fruit set and fruit size, can be considered as different aspects of the same overall strategy, that is, adjusting fruit load to the available resources while striving to achieve the genetically determined fruit size target and the male and female fitness targets.

Transcription factor VviWOX13C regulates fruit set by directly activating VviEXPA37/38/39 in grape (Vitis vinifera L).

KEY MESSAGE: VviWOX13C plays a key regulatory role in the expansin during fruit set. Expansins as a type of non-enzymatic cell wall proteins, are responsible for the loosening and extension in cell walls leading to the enlargement of the plant cells. However, the current studies are still lacking in expansin genes associated with promoting fruit set. Here, 29 members of the expansin gene family were identified in the whole genome of grapes (Vitis vinifera L.), and the functional prediction of expansins was based on the gene annotated information. Results showed that the 29 members of grape expansin gene family could be mainly divided into four subfamilies (EXPA, EXPB, LIKE A, and LIKE B), distributed on 16 chromosomes. Replication analysis showed that there were four segmental duplications and two tandem duplications. Each expansins sequence contained two conserved domain features of grape EXPs (DPBB_1 and Expansin_C) through protein sequence analysis. The transcriptome sequencing results revealed that VviEXPA37, VviEXPA38, and VviEXPA39 were induced and upregulated by CPPU. Furthermore, transcriptional regulatory prediction network indicated that VviWOX13C targeted regulates VviEXPA37, VviEXPA38, and VviEXPA39 simultaneously. EMSA and dual luciferase assays demonstrated that VviWOX13C directly activated the expression of VviEXPA37, VviEXPA38, and VviEXPA39 by directly binding to its promoter. These results provide a basis for further studies on the function and regulatory mechanisms of expansin genes in fruit set.

Effects of Leaf Removal on Free and Glycoconjugate Aromas of Skins and Pulps of Two Italian Red Grapevine Varieties.

Leaf removal is a cultural practice mainly aimed at improving cluster zone microclimates and impacting primary and secondary metabolites, such as volatiles. This research aimed to assess the impact of defoliation on free and glycosylated aromas of a neutral ('Nebbiolo') and a semi-aromatic ('Aleatico') red variety. Defoliation was performed at fruit set (BBCH 71) and, for 'Nebbiolo', also at berries touch (BBCH 81) phenological stages. Skins and pulps were separately analyzed by Solid Phase Extraction-Gas Chromatography/Mass Spectrometry. Results showed that the response to defoliation was variety-dependent. For 'Nebbiolo', especially when performed at the berries' touch stage, defoliation had a significant effect on the accumulation of free volatiles and glycosidic precursors. Differently, free and bound 'Aleatico' volatiles were less impacted by defoliation. Interestingly, in both grapevine varieties, defoliation significantly enhanced the accumulation of aroma precursors in grapes' skins, which is of particular relevance for red wine production and their aging potential. Moreover, results could be helpful for the management of grape quality, as defoliation is currently considered as a strategy to address climate change issues.

Agronomic and hormonal approaches for enhancing flowering intensity in white Guinea yam (Dioscorea rotundata Poir.).

Developing novel white Guinea yam (Dioscorea rotundata) varieties is constrained by the sparse, erratic, and irregular flowering behavior of most genotypes. We tested the effectiveness of nine agronomic and hormonal treatments to enhance flowering on D. rotundata under field conditions. Genotypes responded differently to flower-inducing treatments (p<0.001). Of the test treatments, pruning and silver thiosulfate (STS) were effective in increasing the number of spikes per plant and the flowering intensity on both sparse flowering and monoecious cultivars. STS and tuber removal treatments promoted female flowers on the monoecious variety while pruning and most treatments involving pruning favored male flowers. None of the treatments induced flowering on Danacha, a non-flowering yam landrace. Flower-enhancing treatments had no significant effect on flower fertility translated by the fruit set, since most treatments recorded fruit sets above the species' average crossability rate. Flower-enhancing techniques significantly influenced number of tubers per plant (p = 0.024) and tuber dry matter content (DMC, p = 0.0018) but did not significantly affect plant tuber yield. Nevertheless, treatments that could enhance substantially flowering intensity, such as pruning and STS, reduced tuber yield. DMC had negative associations with all flowering-related traits. This study provided insights into white yam flower induction and suggests promising treatments that can be optimized and used routinely to increase flowering in yam crop, without significantly affecting flower fertility and tuber yield.

MicroRNAs associated with AGL6 and IAA9 function in tomato fruit set.

OBJECTIVE: Fruit set is triggered after ovule fertilization, as a consequence of the downregulation of ovary growth repressors, such as the tomato transcription factors Auxin/indole-3-acetic acid 9 (IAA9) and Agamous-like 6 (AGL6). In a recent work, we developed a method to silence IAA9 and AGL6 in tomato ovaries using exogenous dsRNAs. We also produced small RNA libraries from IAA9- and AGL6-silenced ovaries to confirm the presence of siRNAs, derived from exogenous dsRNA, targeting IAA9 and AGL6. The objective of this work is to exploit these sRNA libraries to identify miRNAs differentially expressed in IAA9- and AGL6-silenced ovaries as compared with unpollinated control ovaries. RESULTS: We identified by RNA sequencing 125 and 104 known and 509 and 516 novel miRNAs from reads mapped to mature or hairpin sequences, respectively. Of the known miRNAs, 7 and 45 were differentially expressed in IAA9- and AGL6-silenced ovaries compared to control ones, respectively. Six miRNAs were common to both datasets, suggesting their importance in the fruit set process. The expression pattern of two of these (miR393 and miR482e-5p) was verified by stem-loop qRT-PCR. The identified miRNAs represent a pool of regulatory sRNAs potentially involved in tomato fruit initiation.