Molecular, hormonal, and metabolic mechanisms of fruit set, the ovary-to-fruit transition, in horticultural crops

Impact of diverse exogenous hormones on parthenocarpy, yield, and quality of pepino (Solanum muricatum) in the Qinghai-Tibet plateau's natural conditions

Pepino (Solanum muricatum), native to the Andes Mountains, requires exogenous hormones in its brief frost-free plateau environment to induce parthenocarpy and ensure yield.The effects of different plant growth regulators and application methods on pepino's growth, yield, and fruit quality were analyzed. Results showed that exogenous plant growth regulators had significant effects on various plant traits For instance, plant height decreased by 43.56% in the flower dipping treatment with 40 parts per million (ppm) 2,4-Dichlorophenoxyacetic acid (2,4-D), while stem diameter decreased by 21.6% with 40 ppm 4-Chlorophenoxyacetic acid (4-CPA) spraying, indicating a notable inhibition of vegetative growth. In contrast, reproductive growth improved, with the 20 ppm 2,4-D spray treatment boosting yield by 627.06% compared to the control. Furthermore, the 30 ppm 2,4-D spray produced the highest single fruit weight, a 69.16% increase over the control. However, exogenous hormones also caused fruit cracking, with the highest rate (55.5%) in the 20 ppm 2,4-D spray treatment. As for fruit quality, glucose content decreased, while fructose and sucrose levels significantly increased in hormone-treated fruits compared to the control. No significant differences were observed in flavonoid, total phenol, or vitamin C content. Transcriptome sequencing showed that 16,836 genes were significantly downregulated in pepino flower buds 72 h after a 30 ppm 4-CPA spray. KEGG enrichment analysis suggested that 4-CPA regulates parthenocarpy by influencing amino acid and protein synthesis pathways. Applying plant growth regulators in different concentrations and methods significantly impacts pepino's growth, yield, and fruit quality. These findings could guide other crops facing similar environmental challenges and potentially transform agricultural practices in high-altitude regions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01533-7.

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.

Genotypic variations in postfertility traits and yield components of mung bean (Vigna radiata (L.) R. Wilczek) germplasms in Chitwan, Nepal

Assessment of economic traits of germplasms, which are associated with genetic variation, is vital for mung improvement. Therefore, by wielding the randomized complete block design with 3 replications, a probe analysis using multiple trait stability indexing and analysis of variance with Duncan's test at p ≤ 0.05 is performed to compare the means of yield attributes. Moreover, simultaneous application of GA3 and NAA (50 mg/L each) was carried out at 30 DAS and at mid-flowering. Pondering not only factorial analysis but also correlation and path studies revealed that flower shedding before and 12 h after spraying is nearly detrimental to yield. In addition, yield/plant was positively (p < 0.001, r = 0.67-0.96) correlated with the harvesting index and test weight. 'Pratigya', demonstrating heightened sensitivity to environmental cues-unveils increased sensitivity-while 'VC3960A-88' flourished with hormone-boosted pod formation. 'VC6368(46-40-3)' packed 11 pods/cluster, and 'CN95' thrived, excelling in abundant grains as well as clusters. Notably, 'VC6370-A' topped yielder, whereas CN95 augmented an efficient harvest index of 0.48. Moreover, path analysis revealed that all postfertility traits are inherently associated with yield. By employing 17 % selection intensity, the MTSI unequivocally ascertained that not only 'VC6370A' but also 'CN95' are the ideal stable and prime performing genotypes for yield(3.04-2.8 tons/ha) as well as interactive traits, a marker for simultaneous selection, as well as improvement. The MTSI view of strengths and weaknesses harbingers that breeders need to focus on increasing the number of genotypes with the desired phenotypes-lower flower abscission, greater grain dimensions and pod setting, harvesting indices, and yields/ha.

A sexually and vegetatively reproducible diploid seedless watermelon inducer via ClHAP2 mutation

Seedless watermelon production relies on triploid cultivation or the application of plant growth regulators. However, challenges such as chromosomal imbalances in triploid varieties and concerns about food safety with growth regulator application impede progress. To tackle these challenges, we developed a sexually and vegetatively reproducible inducer line of diploid seedless watermelon by disrupting the double fertilization process. This innovative approach has enabled the successful induction of diploid seedless watermelon across diverse varieties.

Dynamic temporal transcriptome analysis reveals grape VlMYB59-VlCKX4 regulatory module controls fruit set

Fruit set is a key stage in determining yield potential and guaranteeing quality formation and regulation. N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) has been widely applied in grape production, the most iconic of which is the promotion of grape fruit set. However, current studies still lack the molecular mechanism of CPPU-induced grape fruit set. Here, the dynamic, high-resolution stage-specific transcriptome profiles were generated based on two different treatments and five developmental periods during fruit set in 'Kyoho' grape (Vitis vinifera L. × V. labrusca L.). Pairwise comparison and functional category analysis showed that phytohormone action cytokinin was significantly enriched during the CPPU-induced grape fruit set, but not the natural one. Value differentially expressed gene (VDEG) was a newly proposed analysis strategy for mining genes related to the grape fruit set. Notably, the cytokinin metabolic process was significantly enriched among up-regulated VDEGs. Of importance, a key VDEG VlCKX4 related to the cytokinin metabolic process was identified as related to the grape fruit set. Overexpression of VlCKX4 gene promoted the Arabidopsis plants that produce more and heavier siliques. The transcription factor VlMYB59 directly bound to the promoter of VlCKX4 and activated its expression. Moreover, overexpression of VlMYB59 gene also promoted the Arabidopsis fruit set. Overall, VlMYB59 responded to CPPU treatment and directly activated the expression of VlCKX4, thus promoting the fruit set. A regulatory pathway of the VlMYB59-VlCKX4 module in the fruit set was uncovered, which provides important insights into the molecular mechanisms of the fruit set and good genetic resources for high fruit set rate breeding.

Comparative transcriptome analysis of two pomelo accessions with different parthenocarpic ability provides insight into the molecular mechanisms of parthenocarpy in pomelo (Citrus grandis)

Parthenocarpy is an important way for seedless fruit production in citrus. However, the molecular mechanism(s) of parthenocarpy in pomelo is still unknown. Our initial study found significantly different parthenocarpic abilities in Guanximiyou (G) and Shatianyou (S) pomelo following emasculation, and an endogenous hormone content assay revealed that indole-3-acetic acid (IAA), gibberellic acid (GA3) and zeatin (ZT) jointly promoted fruit expansion and cell division in parthenocarpic pomelo (G pomelo). To unravel the underlying molecular mechanism(s), we conducted the first transcriptome analysis on the two pomelo accessions at these two critical stages: the fruit initiation stage and the rapid expansion stage, in order to identify genes associated with parthenocarpy. This analysis yielded approximately 7.86 Gb of high-quality reads, and the subsequent de novo assembly resulted in the identification of 5,792 DEGs (Differentially Expressed Genes). Among these, a range of transcription factor families such as CgERF, CgC2H2, CgbHLH, CgNAC and CgMYB, along with genes like CgLAX2, CgGH3.6 and CgGH3, emerged as potential candidates contributing to pomelo parthenocarpy, as confirmed by qRT-PCR analysis. The present study provides comprehensive transcriptomic profiles of both parthenocarpic and non-parthenocarpic pomelos, reveals several metabolic pathways linked to parthenocarpy, and highlights the significant role of plant hormones in its regulation. These findings deepen our understanding of the molecular mechanisms underlying parthenocarpy in pomelo.

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.

Galactinol synthase 2 influences the metabolism of chlorophyll, carotenoids, and ethylene in tomato fruits

Galactinol synthase (GolS), which catalyses the synthesis of galactinol, is the first critical enzyme in the biosynthesis of raffinose family oligosaccharides (RFOs) and contributes to plant growth and development, and resistance mechanisms. However, its role in fruit development remains largely unknown. In this study, we used CRISPR/Cas9 gene-editing technology in tomato (Solanum lycopersicum) to create the gols2 mutant showing uniformly green fruits without dark-green shoulders, and promoting fruit ripening. Analysis indicated that galactinol was undetectable in the ovaries and fruits of the mutant, and the accumulation of chlorophyll and chloroplast development was suppressed in the fruits. RNA-sequencing analysis showed that genes related to chlorophyll accumulation and chloroplast development were down-regulated, including PROTOCHLOROPHYLLIDE OXIDOREDUCTASE, GOLDEN 2-LIKE 2, and CHLOROPHYLL A/B-BINDING PROTEINS. In addition, early color transformation and ethylene release was prompted in the gols2 lines by regulation of the expression of genes involved in carotenoid and ethylene metabolism (e.g. PHYTOENE SYNTHASE 1, CAROTENE CIS-TRANS ISOMERASE, and 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHASE2/4) and fruit ripening (e.g. RIPENING INHIBITOR, NON-RIPENING, and APETALA2a). Our results provide evidence for the involvement of GolS2 in pigment and ethylene metabolism of tomato fruits.

Variations in Fruit Ploidy Level and Cell Size between Small- and Large-Fruited Olive Cultivars during Fruit Ontogeny

Olive (Olea europaea L.) is one of the major oil fruit tree crops worldwide. However, the mechanisms underlying olive fruit growth remain poorly understood. Here, we examine questions regarding the interaction of endoreduplication, cell division, and cell expansion with olive fruit growth in relation to the final fruit size by measuring fruit diameter, pericarp thickness, cell area, and ploidy level during fruit ontogeny in three olive cultivars with different fruit sizes. The results demonstrate that differences in the fruit size are related to the maximum growth rate between olive cultivars during early fruit growth, about 50 days post-anthesis (DPA). Differences in fruit weight between olive cultivars were found from 35 DPA, while the distinctive fruit shape became detectable from 21 DPA, even though the increase in pericarp thickness became detectable from 7 DPA in the three cultivars. During early fruit growth, intense mitotic activity appeared during the first 21 DPA in the fruit, whereas the highest cell expansion rates occurred from 28 to 42 DPA during this phase, suggesting that olive fruit cell number is determined from 28 DPA in the three cultivars. Moreover, olive fruit of the large-fruited cultivars was enlarged due to relatively higher cell division and expansion rates compared with the small-fruited cultivar. The ploidy level of olive fruit pericarp between early and late growth was different, but similar among olive cultivars, revealing that ploidy levels are not associated with cell size, in terms of different 8C levels during olive fruit growth. In the three olive cultivars, the maximum endoreduplication level (8C) occurred just before strong cell expansion during early fruit growth in fruit pericarp, whereas the cell expansion during late fruit growth occurred without preceding endoreduplication. We conclude that the basis for fruit size differences between olive cultivars is determined mainly by different cell division and expansion rates during the early fruit growth phase. These data provide new findings on the contribution of fruit ploidy and cell size to fruit size in olive and ultimately on the control of olive fruit development.

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.