Abstract
Ethylene is a gaseous phytohormone involved in various physiological processes, including fruit ripening, senescence, root hair development and stress responses. Recent genomics studies have ...suggested that most homologous genes of ethylene biosynthesis and signaling are conserved from algae to angiosperms, whereas the function and biosynthesis of ethylene remain unknown in basal plants. Here, we examined the physiological effects of ethylene, an ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC) and an inhibitor of ethylene perception, silver thiosulfate (STS), in a basal land plant, Marchantia polymorpha. M. polymorpha plants biosynthesized ethylene, and treatment with high concentrations of ACC slightly promoted ethylene production. ACC remarkably suppressed the growth of thalli (vegetative organs) and rhizoids (root-hair-like cells), whereas exogenous ethylene slightly promoted thallus growth. STS suppressed thallus growth and induced ectopic rhizoid formation on the dorsal surface of thalli. Thus, ACC and ethylene have different effects on the vegetative growth of M. polymorpha. We generated single and double mutants of ACC synthase-like (ACSL) genes, MpACSL1 and MpACSL2. The mutants did not show obvious defects in thallus growth, ACC content and ethylene production, indicating that MpACSL genes are not essential for the vegetative growth and biosynthesis of ACC and ethylene. Gene expression analysis suggested the involvement of MpACSL1 and MpACSL2 in stress responses. Collectively, our results imply ethylene-independent function of ACC and the absence of ACC-mediated ethylene biosynthesis in M. polymorpha.
•Chitosan/alginate based LBL edible coating extended shelf life of ‘Kosui’ pear fruit.•The LBL edible coating suppressed fruit ethylene production and respiration rates.•The LBL edible coating did ...not affect fruit weight loss.•Genes related with ethylene production, softening, and color change were repressed.•Glycolytic pathway genes were upregulated, while TCA cycle genes were repressed.
Edible coatings attract much interest today as safe and effective techniques for maintaining quality and extending shelf life of fruit and vegetables. However, the underlying molecular mechanisms remain unclear. The aim of this study was to identify genes involved in enhancement of shelf life in ‘Kosui’ Japanese pear (Pyrus pyrifolia Nakai) fruit by chitosan/alginate-based layer-by-layer (LBL) edible coatings. Both tri-layer and penta-layer LBL coatings effectively minimized fruit respiration and ethylene production rates, inhibited flesh firmness loss, and prevented peel color change for 21 d at 20 °C but had little effect on weight loss. Gas permeability tests on polyethylene terephthalate films revealed that LBL coatings substantially lowered oxygen transmission rates but had little effect on water vapor transmission rate. In an attempt to identify the pathways involved, we monitored gene expression in LBL-coated and uncoated fruit by RNA-Seq analysis. This analysis revealed a clear downregulation of genes associated with ethylene production and fruit ripening, as well as the tricarboxylic acid cycle following application of LBL edible coating. On the other hand, genes associated with the glycolysis pathway were mostly upregulated. Together, these results indicate that prolonged shelf life by chitosan/alginate-based LBL edible coating could primarily result from control of the balance of aerobic-anaerobic metabolism.
In the evolutionary history of plants, variation in cis-regulatory elements (CREs) resulting in diversification of gene expression has played a central role in driving the evolution of ...lineage-specific traits. However, it is difficult to predict expression behaviors from CRE patterns to properly harness them, mainly because the biological processes are complex. In this study, we used cistrome datasets and explainable convolutional neural network (CNN) frameworks to predict genome-wide expression patterns in tomato (Solanum lycopersicum) fruit from the DNA sequences in gene regulatory regions. By fixing the effects of trans-acting factors using single cell-type spatiotemporal transcriptome data for the response variables, we developed a prediction model for crucial expression patterns in the initiation of tomato fruit ripening. Feature visualization of the CNNs identified nucleotide residues critical to the objective expression pattern in each gene, and their effects were validated experimentally in ripening tomato fruit. This cis-decoding framework will not only contribute to the understanding of the regulatory networks derived from CREs and transcription factor interactions, but also provides a flexible means of designing alleles for optimized expression.
Peel degreening is an important aspect of fruit ripening in many citrus fruit, and previous studies have shown that it can be advanced by ethylene treatment or by low-temperature storage. However, ...the important regulators and pathways involved in natural peel degreening remain largely unknown. To determine how natural peel degreening is regulated in lemon fruit (Citrus limon), we studied transcriptome and physiochemical changes in the flavedo in response to ethylene treatment and low temperatures. Treatment with ethylene induced rapid peel degreening, which was strongly inhibited by the ethylene antagonist, 1-methylcyclopropene (1-MCP). Compared with 25 ºC, moderately low storage temperatures of 5-20 °C also triggered peel degreening. Surprisingly, repeated 1-MCP treatments failed to inhibit the peel degreening induced by low temperature. Transcriptome analysis revealed that low temperature and ethylene independently regulated genes associated with chlorophyll degradation, carotenoid metabolism, photosystem proteins, phytohormone biosynthesis and signalling, and transcription factors. Peel degreening of fruit on trees occurred in association with drops in ambient temperature, and it coincided with the differential expression of low temperature-regulated genes. In contrast, genes that were uniquely regulated by ethylene showed no significant expression changes during on-tree peel degreening. Based on these findings, we hypothesize that low temperature plays a prominent role in regulating natural peel degreening independently of ethylene in citrus fruit.
Fruit quality is determined by multiple complex traits, which are difficult to diagnose by simple criteria and often require expert skills with a long experience. Nevertheless, current fruit sorting ...systems need a non-destructive, costless, and more rapid evaluation of fruit qualities. For peach, although many techniques have been developed for diagnosing fruit (internal) traits that determine commercial values, those techniques often require special facilities with high costs or take a long time for an assessment. Our study aimed to apply deep learning technology to evaluate multiple peach fruit traits using only simple RGB images for practical applications. We targeted seven fruit traits fundamentally involving commercial fruit quality; skin color, flesh firmness, sugar content, and four internal disorders, including colorless early softening, split-pit, watercore, and damage from peach fruit moth. We performed binary classification and regression analysis for these traits by convolutional neural networks (CNNs). Binary classification is performed to judge whether a fruit trait exceeds a threshold or not for a given image. Regression analysis is performed to estimate the degree of a trait quantitatively. Their results suggested that CNNs can successfully diagnose multiple fruit traits and predict quantitative values from RGB images. We also applied an explainable AI (X-AI) technique to spot the hypothetical symptoms for each trait on a fruit image, giving novel interpretations for physiological reactions associated with each fruit trait.
•Implementable peach fruit sorting needs automatic evaluation for multiple traits.•With CNN models, seven important fruit traits were diagnosable from photo images.•Xception regression model allowed estimation of quantitative traits in peach fruit.•Explainable AI technique could spot the premonitory symptoms of fruit disorders.
Abstract
Aluminum (Al)-tolerant tobacco cell line ALT301 derived from SL (wild-type) hardly exhibits Al-triggered reactive oxygen species (ROS) compared with SL. Molecular mechanism leading to this ...phenotype was investigated comparatively with SL. Under normal growth condition, metabolome data suggested the activation of glycolysis and lactate fermentation but the repression of the tricarboxylic acid (TCA) cycle in ALT301, namely aerobic fermentation, which seemed to be transcriptionally controlled partly by higher expression of genes encoding lactate dehydrogenase and pyruvate dehydrogenase kinase. Microarray and gene ontology analyses revealed the upregulation of the gene encoding related to APETALA2.3 (RAP2.3)-like protein, one of the group VII ethylene response factors (ERFVIIs), in ALT301. ERFVII transcription factors are known to be key regulators for hypoxia response that promotes substrate-level ATP production by glycolysis and fermentation. ERFVIIs are degraded under normoxia by the N-end rule pathway of proteolysis depending on both oxygen and nitric oxide (NO), and NO is produced mainly by nitrate reductase (NR) in plants. In ALT301, levels of the NR gene expression (NIA2), NR activity and NO production were all lower compared with SL. Consistently, the known effects of NO on respiratory pathways were also repressed in ALT301. Under Al-treatment condition, NO level increased in both lines but was lower in ALT301. These results suggest that the upregulation of the RAP2.3-like gene and the downregulation of the NIA2 gene and resultant NO depletion in ALT301 coordinately enhance aerobic fermentation, which seems to be related to a higher capacity to prevent ROS production in mitochondria under Al stress.
A major challenge in terms of commercializing 1-methylclopropene (1-MCP) to extend the storage life and control physiological disorders in European pears is that it irreversibly inhibits fruit ...ripening in some cultivars, particularly flesh softening that is necessary for optimal consumption quality. In this study, we examined the effect of 1-MCP pretreatments on fruit ripening and associated transcriptomic changes in ‘La France’ (Pyrus communis L.) pears during storage at 20°C and 5°C. Compared to non-treated controls, 1-MCP pretreatment suppressed fruit respiration and ethylene production rates, and markedly delayed flesh softening. Normal ripening (ethylene production and flesh softening to eating quality firmness) was observed in 1-MCP treated fruit after 42 d at 20°C, and 112 d at 5°C. Subsequent RNA-Seq analysis revealed that 6,427 genes, including those associated with ethylene biosynthesis (ACS1, ACS1b, ACO1, and ACO2), cell wall degrading enzymes (PG3, β-GAL, EG, and EXP1), and transcription factors (AGL18 and NAC29) were up- or down-regulated in non-treated fruit both at 20°C and 5°C. The expression patterns of these genes were disrupted by 1-MCP pretreatment, but up- or down-regulation was also observed when ethylene was detected in 1-MCP-treated fruit. Together, these findings demonstrate the potential for practical use of 1-MCP to extend storage life in ‘La France’ pears given that (i) a single application markedly extended storage life to 56 d at 20°C and 112 d at 5°C, and (ii) treated fruit could regain their softening capacity, thus eliminating previous irreversible ripening blockage concerns.
In contrast to the progress in the research on physiological disorders relating to shelf life in fruit crops, it has been difficult to non-destructively predict their occurrence. Recent high-tech ...instruments have gradually enabled non-destructive predictions for various disorders in some crops, while there are still issues in terms of efficiency and costs. Here, we propose application of a deep neural network (or simply deep learning) to simple RGB images to predict a severe fruit disorder in persimmon, rapid over-softening. With 1,080 RGB images of ‘Soshu’ persimmon fruits, three convolutional neural networks (CNN) were examined to predict rapid over-softened fruits with a binary classification and the date to fruit softening. All of the examined CNN models worked successfully for binary classification of the rapid over-softened fruits and the controls with > 80% accuracy using multiple criteria. Furthermore, the prediction values (or confidence) in the binary classification were correlated to the date to fruit softening. Although the features for classification by deep learning have been thought to be in a black box by conventional standards, recent feature visualization methods (or “explainable” deep learning) has allowed identification of the relevant regions in the original images. We applied Grad-CAM, Guided backpropagation, and layer-wise relevance propagation (LRP), to find early symptoms for CNNs classification of rapid over-softened fruits. The focus on the relevant regions tended to be on color unevenness on the surface of the fruit, especially in the peripheral regions. These results suggest that deep learning frameworks could potentially provide new insights into early physiological symptoms of which researchers are unaware.
The objective of this study was to evaluate the physico-chemical and postharvest quality characteristics of intra- and interspecific grafted tomato fruit. Anna F1, a commercial tomato variety was ...interspecifically (Tomato Scion and African eggplant rootstock (Solanum aethiopicum)) and intraspecifically (Tomato Scion and bacterial wilt resistant hybrid tomato rootstock) grafted. The tomatoes were grown in a greenhouse and harvested at mature green, turning and ripe stages respectively. The tomatoes were analyzed for size, weight, cumulative weight loss, color changes, texture, respiration and ethylene gas production rates, vitamin C and lycopene content. Interspecific grafting on Manyire green, AB2, and intraspecific grafting on Armada, and B.B rootstocks significantly improved physical and physiological attributes of the tomato fruit. There was significant difference (p < 0.05) in size and weight of grafted tomatoes and control at all the three maturity stages. Intraspecific grafted tomato fruits on Armada rootstocks had the best quality characteristics in terms of firmness, low weight loss, respiration and ethylene production rates which are associated with extended postharvest shelf-life. Intraspecific grafting reduced respiration and ethylene gas production rates with tomatoes grafted onto Armada rootstocks attaining the least climacteric peaks of 20.20 ml CO2 Kg-1h-1 and 0.34 μL C2H4 Kg-1h-1 respectively at mature green stage, thus leading to extendend postharvest life of these tomatoes. Tomatoes grafted onto B.B rootstock had the highest vitamin C content (28.11 mg/100 g). In general, intraspecific grafting recorded the best quality traits over the interspecific grafting. However interspecific grafting of tomato onto African eggplant Manyire and AB2 rootstocks had lower but comparable fruit quality to intraspecific grafting.
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•The effect of grafting on tomato quality is dependent on scion/rootstock combination.•Tomatoes from Manyire and AB2 rootstocks grafts (interspecific), and Armada and B.B rootstocks (intraspecific) had improved physical, physiological qualities as compared to nongrafted control.•Fruits from the Armada rootstock reported the best quality characteristics in terms of firmness and low weight loss, respiration and ethylene production rates which are associated with prolonging shelf-life.•Lycopene content was not affected by grafting.•In general, intraspecific grafting had the best quality traits over the interspecific grafting. However interspecific grafting of tomato onto African eggplant Manyire and AB2 rootstocks has comparable fruit quality to intraspecific grafting especially for resource poor farmers.
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