Atemoya fruit development and cytological aspects of GA3-induced growth and 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.

Transcriptomic and genetic approaches reveal that the pipecolate biosynthesis pathway simultaneously regulates tomato fruit ripening and quality

Pipecolic acid (Pip) and N-hydroxypipecolic acid (NHP) have been found to accumulate during the ripening of multiple types of fruits; however, the function and mechanism of pipecolate pathway in fruits remain unclear. Here study was conducted on fruits produced by the model plant tomato, wherein the NHP biosynthesis-related genes, Slald1 and Slfmo1, were mutated. The results showed that the fruits of both the Slald1 and the Slfmo1 mutants exhibited a delayed onset of ripening, decreased fruit size, nutrition and flavor. Exogenous treatment with Pip and NHP promoted fruit ripening and improved fruit quality. Transcriptomic analysis combined with weighted gene co-expression network analysis revealed that the genes involved in the biosynthesis of amino acids, carbon metabolism, photosynthesis, starch and sucrose metabolism, flavonoid biosynthesis, and plant hormone signal transduction were affected by SlFMO1 gene mutation. Transcription factor prediction analysis revealed that the NAC and AP2/ERF-ERF family members are notably involved in the regulation pathway. Overall, our results suggest that the pipecolate biosynthesis pathway is involved in the simultaneous regulation of fruit ripening and quality and indicate that a regulatory mechanism at the transcriptional level exists. However, possible roles of endogenously synthesized Pip and NHP in these processes remain to be determined. The biosynthesis pathway genes SlALD1 and SlFMO1 may be potential breeding targets for promoting fruit ripening and improving fruit quality with concomitant yield increases.

Pericarp histogenesis and histochemistry during fruit development in Butia capitata (Arecaceae)

Palm fruits show great structural complexity, and in-depth studies of their development are still scarce. This work aimed to define the developmental stages of the fruit of the neotropical palm Butia capitata and to characterize the ontogenesis of its pericarp. Biometric, anatomical, and histochemical evaluations were performed on pistillate flowers and developing fruits. The whole fruit develops in three phases: (I) histogenesis (up to 42 days after anthesis - DAA), when the topographic regions of the pericarp are defined; (II) pyrene maturation (42 to 70 DAA), when the sclerified zone of the pericarp is established; and (III) mesocarp maturation (70 to 84 DAA), when reserve deposition is completed. During pericarp ontogenesis (i) the outer epidermis and the outer mesophyll of the ovary give origin to the exocarp (secretory epidermis, collenchyma, parenchyma, sclerenchyma, and vascular bundles); (ii) the median ovarian mesophyll develops into the mesocarp, with two distinct topographical regions; (iii) the inner ovarian epidermis originates the endocarp; and in the micropylar region, it differentiates into the germination pore plate, a structure that protects the embryo and controls germination. (iv) Most of the inner region of the mesocarp fuses with the endocarp and, both lignified, give rise to the stony pyrene; (v) in the other regions of the mesocarp, carbohydrates and lipids are accumulated in a parenchyma permeated with fiber and vascular bundles. The development of the B. capitata pericarp presents high complexity and a pattern not yet reported for Arecaceae, which supports the adoption of the Butia-type pyrenarium fruit class.

A Flashforward Look into Solutions for Fruit and Vegetable Production

One of the most important challenges facing current and future generations is how climate change and continuous population growth adversely affect food security. To address this, the food system needs a complete transformation where more is produced in non-optimal and space-limited areas while reducing negative environmental impacts. Fruits and vegetables, essential for human health, are high-value-added crops, which are grown in both greenhouses and open field environments. Here, we review potential practices to reduce the impact of climate variation and ecosystem damages on fruit and vegetable crop yield, as well as highlight current bottlenecks for indoor and outdoor agrosystems. To obtain sustainability, high-tech greenhouses are increasingly important and biotechnological means are becoming instrumental in designing the crops of tomorrow. We discuss key traits that need to be studied to improve agrosystem sustainability and fruit yield.

Plant Development and Crop Yield: The Role of Gibberellins

Gibberellins have been classically related to a few key developmental processes, thus being essential for the accurate unfolding of plant genetic programs. After more than a century of research, over one hundred different gibberellins have been described. There is a continuously increasing interest in gibberellins research because of their relevant role in the so-called "Green Revolution", as well as their current and possible applications in crop improvement. The functions attributed to gibberellins have been traditionally restricted to the regulation of plant stature, seed germination, and flowering. Nonetheless, research in the last years has shown that these functions extend to many other relevant processes. In this review, the current knowledge on gibberellins homeostasis and mode of action is briefly outlined, while specific attention is focused on the many different responses in which gibberellins take part. Thus, those genes and proteins identified as being involved in the regulation of gibberellin responses in model and non-model species are highlighted. The present review aims to provide a comprehensive picture of the state-of-the-art perception of gibberellins molecular biology and its effects on plant development. This picture might be helpful to enhance our current understanding of gibberellins biology and provide the know-how for the development of more accurate research and breeding programs.

Identification and Characterization of AUXIN Response Factor Gene Family Reveals Their Regulatory Network to Respond the Multi-Hormones Crosstalk during GA-Induced Grape Parthenocarpic Berry

Exogenous gibberellin (GA) was widely used to improve berry quality through inducing parthenocarpic seedless berries in grapes. We revealed that auxin response factors (ARFs), the key transcription factors in response to auxin, might respond to GA involving modulation of grape parthenocarpy. However, the underlying molecular mechanism in this process remains yet unclear. Here, a total of 19 VvARF members were identified in the ovaries during GA-induced grapes’ parthenocarpy. Interestingly, almost all members were GA-responsive factors, of which 9 could be classified in plant hormone signal transduction (KO04075) and involved in the tryptophan metabolic pathway (K14486). Moreover, VvARFs were predicted to have 310 interacted proteins involved in 19 KEGG pathways. Of them, 32 interacted proteins participated in the KO04075 pathway, including auxin (IAA), salicylic acid (SA), abscisic acid (ABA), cytokinin (CTK), and ethylene signaling pathways by responding to GA-mediated multi-hormone crosstalk. Further analysis demonstrated that VvARF4-2 might be the major factor in the modulation of GA-induced parthenocarpy via the crosstalk of IAA, CTK, SA, and ethylene signaling, followed by VvARF6-1 and VvARF9 involved in SA and ABA signaling pathways, respectively. Finally, we developed a VvARFs-mediated regulatory network by responding to GA-mediated multi-hormone crosstalk during grape parthenocarpy. Collectively, our findings provided novel insights into the regulatory network of VvARFs in GA-guided multi-hormone signaling to modulate grape parthenocarpy, which has great implications for the molecular breeding of high quality seedless grape berries.

Dissecting Breeders' Sense via Explainable Machine Learning Approach: Application to Fruit Peelability and Hardness in Citrus

"Genomics-assisted breeding", which utilizes genomics-based methods, e.g., genome-wide association study (GWAS) and genomic selection (GS), has been attracting attention, especially in the field of fruit breeding. Low-cost genotyping technologies that support genome-assisted breeding have already been established. However, efficient collection of large amounts of high-quality phenotypic data is essential for the success of such breeding. Most of the fruit quality traits have been sensorily and visually evaluated by professional breeders. However, the fruit morphological features that serve as the basis for such sensory and visual judgments are unclear. This makes it difficult to collect efficient phenotypic data on fruit quality traits using image analysis. In this study, we developed a method to automatically measure the morphological features of citrus fruits by the image analysis of cross-sectional images of citrus fruits. We applied explainable machine learning methods and Bayesian networks to determine the relationship between fruit morphological features and two sensorily evaluated fruit quality traits: easiness of peeling (Peeling) and fruit hardness (FruH). In each of all the methods applied in this study, the degradation area of the central core of the fruit was significantly and directly associated with both Peeling and FruH, while the seed area was significantly and directly related to FruH alone. The degradation area of albedo and the area of flavedo were also significantly and directly related to Peeling and FruH, respectively, except in one or two methods. These results suggest that an approach that combines explainable machine learning methods, Bayesian networks, and image analysis can be effective in dissecting the experienced sense of a breeder. In breeding programs, collecting fruit images and efficiently measuring and documenting fruit morphological features that are related to fruit quality traits may increase the size of data for the analysis and improvement of the accuracy of GWAS and GS on the quality traits of the citrus fruits.

Gibberellic Acid (GA3) Applied to Flowering Heracleum sosnowskyi Decreases Seed Viability Even If Seed Development Is Not Inhibited

Sosnowsky’s hogweed (Heracleum sosnowskyi Manden.), an important invasive species in Eastern Europe, is a monocarpic perennial plant that propagates exclusively by seeds. Hence, interfering with seed viability could help control its spread. In the present study, we investigated the effect of exogenous GA₃ (25, 100 and 150 mg/L) sprayed twice onto flowering H. sosnowskyi plants on the development of fruits (mericarps) and their ability to germinate under field conditions over the growing seasons of 2018 and 2019. Mericarps from plants sprayed with GA₃ failed to develop normally. The width/length ratio of mericarps decreased by 23% to 25% after 150 mg/L GA₃ application and their average weight decreased between 7% and 39% under all GA₃ treatments. X-ray radiographs revealed that the internal structure was malformed, with many of the mericarps lacking well-developed seeds. Proportionally fewer well-developed mericarps were produced by GA₃-treated plants than water-sprayed control plants in 2018. Seed germination assessed outdoors in seeds buried in the ground was also severely reduced (from 58% to 99% after 150 mg/L GA₃ application). This indicates that exogenous GA₃ sprays result in incomplete seed development and a consequent decrease in viability and germination. As the highest GA₃ dose used resulted in significantly reduced propagation of Sosnowsky’s hogweed through seeds in the field, GA₃ provides a promising approach to the control of the spread of this invasive weed species.