Ethylene Biosynthesis Research Articles

Comparative Analysis of Gene Expression between Early Maturation Mutant ‘Beni Shogun’ and ‘Fuji’ Cultivars during Fruit Development and Ripening

We aimed to compare the maturation and ripening characteristics of two apple cultivars, early maturation mutant ‘Beni Shogun’ and ‘Fuji’. The study revealed that both cultivars reached full bloom on the same day, but ‘Beni Shogun’ matured earlier than ‘Fuji’. In addition, differences were observed in fruit size, length, width, sweetness, acidity, and ethylene production levels. The study also examined the expression patterns of genes involved in ethylene biosynthesis and signal transduction, as well as those involved in auxin signal transduction and transcriptional regulation, to investigate the putative molecular mechanism behind the distinct fruit development, maturation, and ripening. The expression of the MdACO1 gene showed a sharp increase after the maturation date, whereas the expression of the MdACO7 gene was higher in the early and middle stages of fruit development. The clustering analysis provided insights into the correlation between the phenotypic traits and expression levels of the key genes. They were categorized into three clusters, and the third cluster consisted of six phenotypes, including fruit size, length, width, sweetness, starch content, and ethylene production, as well as the one gene MdACO1. These findings suggest that ‘Beni Shogun’ and ‘Fuji’ have distinct fruit development and ripening behaviors, with ‘Beni Shogun’ maturing earlier than ‘Fuji’.

Cross-Talk and Physiological Role of Jasmonic Acid, Ethylene, and Reactive Oxygen Species in Wound-Induced Phenolic Biosynthesis in Broccoli.

Wounding induces phenolic biosynthesis in broccoli. However, there is scarce information about the physiological and molecular mechanisms governing this stress response. In the present study, a chemical-genetics approach was used to elucidate the role of reactive oxygen species (ROS), jasmonic acid (JA), and ethylene (ET) as stress-signaling molecules in the wound-induced phenolic biosynthesis in broccoli. Wounding activated the biosynthesis of ET and JA. Likewise, the wound-induced biosynthesis of ET and JA was regulated by ROS. JA activated primary metabolism, whereas the three signaling molecules activated phenylpropanoid metabolism. The signaling molecules inhibited the wound-induced activation of the hydroxycinnamoyl-CoA quinate hydroxycinnamoyl transferase (HQT) gene, which is involved in caffeoylquinic acids biosynthesis, and the main phenolics accumulated in wounded broccoli, suggesting that an alternative caffeoylquinic biosynthesis pathway is activated in the tissue due to wounding. ROS mediated the biosynthesis of most individual phenolic compounds evaluated. In conclusion, ROS, ET, and JA are essential in activating broccoli's primary and secondary metabolism, resulting in phenolic accumulation.

The microRNA ppe-miR393 mediates auxin-induced peach fruit softening by promoting ethylene production.

Auxin can inhibit or promote fruit ripening, depending on the species. Melting flesh (MF) peach fruit (Prunus persica L. Batsch) cultivars produce high levels of ethylene caused by high concentrations of indole-3-acetic acid (IAA), which leads to rapid fruit softening at the late stage of development. In contrast, due to the low concentrations of IAA, the fruit of stony hard (SH) peach cultivars does not soften and produces little ethylene. Auxin seems necessary to trigger the biosynthesis of ethylene in peach fruit; however, the mechanism is not well understood. In this study, we identified miRNA gene family members ppe-miR393a and ppe-miR393b that are differentially expressed in SH and MF fruits. RNA ligase-mediated 5' rapid amplification of cDNA ends and transient transformation of Nicotiana benthamiana revealed TRANSPORT INHIBITOR RESPONSE 1 (PpTIR1), part of the auxin perception and response system, as a target of ppe-miR393a and b. Yeast 2-hybrid assay and bimolecular fluorescence complementation assay revealed that PpTIR1 physically interacts with an Aux/IAA protein PpIAA13. The results of yeast 1-hybrid assay, electrophoretic mobility shift assay, and dual-luciferase assay indicated that PpIAA13 could directly bind to and trans-activate the promoter of 1-aminocyclopropane-1-carboxylic acid synthase 1 (PpACS1), required for ethylene biosynthesis. Transient overexpression and suppression of ppe-miR393a and PpIAA13 in peach fruit induced and repressed the expression of PpACS1, confirming their regulatory role in ethylene synthesis. Gene expression analysis in developing MF and SH fruits, combined with postharvest α-naphthalene acetic acid (NAA) treatment, supports a role for a ppe-miR393-PpTIR1-PpIAA13-PpACS1 module in regulating auxin-related differences in ethylene production and softening extent in different types of peach.

Transcriptional regulation of MbACO2-mediated ethylene synthesis during postharvest banana ripening

Ethylene plays a central role in climacteric fruit ripening. 1-Aminocyclopropane-1-carboxylic acid oxidase (ACO) is a crucial enzyme for ethylene biosynthesis. Edible cultivated banana varieties are mainly composed of the A- or A/B-genome. Nevertheless, the function and regulatory mechanism of ACO genes in the B-genome of banana fruit are unknown. The present study revealed the function and regulatory mechanism of the B-genome-specific gene MbACO2 in ethylene biosynthesis during postharvest banana ripening. MbACO2 expression significantly increased at 6 d postharvest. MbACO2 overexpression in tomato resulted in an increase in ethylene biosynthesis and the acceleration of fruit ripening. MaNAC29 and MbERF71/MbERF113 showed induction during the postharvest periods and directly activated the transcription of MbACO2 through the CGTC-element and GCC-box in its promoter, respectively. In addition, MaMAPK1 interacted with MaNAC29 to further enhance the transcription of MbACO2. Collectively, our findings demonstrate a novel regulatory cascade involving MaMAPK1, MaNAC29, and MbERF71/MbERF113 that promotes MbACO2 transcription during postharvest banana ripening, which helps design breeding strategies to extend the shelf life of fruit.

Ethanol fermentation- and ethylene physiology-related gene expression profiles in Red Delicious apples stored under variable hypoxic conditions and protocols

Dynamic Controlled Atmosphere (DCA) is beneficial in maintaining specific quality parameters but, due to the extreme oxygen levels applied, can cause adverse effects on the fruit by inducing excessive anaerobic metabolism and the production of off-flavors. The metabolic adaptation and responses of apples (Malus domestica Borkh.) cv. Red Delicious to static or dynamic oxygen concentrations (0.3 and 0.8%, with sequential shifts) during cold storage for 7 months were studied by monitoring quality parameters and the expression of genes involved in sugar, fermentative metabolism, and ethylene physiology. Ethanol content reached the highest levels (around 400 mg/kg FW) under 0.3% oxygen concentration and fruit firmness appeared to be reduced in samples accumulating the highest levels of ethanol. Oxygen switch was effective in reducing the ethanol concentrations with timing-dependent variable effects. The expression of fermentative (alcohol dehydrogenase, lactate dehydrogenase, pyruvate decarboxylase) and sugar metabolism (β-amylase; phosphofructokinase; sucrose synthase) genes resulted to be differently affected by the hypoxic conditions imposed, in particular during the early stages of storage. Sucrose synthase expression appeared to be highly sensitive to changes in low oxygen concentration. Ethylene biosynthesis (ACC synthase and oxidase) genes showed marked differences in their expression in relation to the static and dynamic protocols and the hypoxic conditions, as well as six Ethylene Responsive Factors (ERF) genes, some of them possibly involved in the oxygen sensing mechanism operating in fruit tissues.

Citrus ACC synthase CiACS4 regulates plant height by inhibiting gibberellin biosynthesis.

Dwarfism is an agronomic trait that has substantial effects on crop yield, lodging resistance, planting density, and a high harvest index. Ethylene plays an important role in plant growth and development, including the determination of plant height. However, the mechanism by which ethylene regulates plant height, especially in woody plants, remains unclear. In this study, a 1-aminocyclopropane-1-carboxylic acid synthase (ACC) gene (ACS), which is involved in ethylene biosynthesis, was isolated from lemon (Citrus limon L. Burm) and named CiACS4. Overexpression of CiACS4 resulted in a dwarf phenotype in Nicotiana tabacum and lemon and increased ethylene release and decreased gibberellin (GA) content in transgenic plants. Inhibition of CiACS4 expression in transgenic citrus significantly increased plant height compared with the controls. Yeast two-hybrid assays revealed that CiACS4 interacted with an ethylene response factor (ERF), CiERF3. Further experiments revealed that the CiACS4-CiERF3 complex can bind to the promoters of 2 citrus GA20-oxidase genes, CiGA20ox1 and CiGA20ox2, and suppress their expression. In addition, another ERF transcription factor, CiERF023, identified using yeast one-hybrid assays, promoted CiACS4 expression by binding to its promoter. Overexpression of CiERF023 in N. tabacum caused a dwarfing phenotype. CiACS4, CiERF3, and CiERF023 expression was inhibited and induced by GA3 and ACC treatments, respectively. These results suggest that the CiACS4-CiERF3 complex may be involved in the regulation of plant height by regulating CiGA20ox1 and CiGA20ox2 expression levels in citrus.

Comprehensive transcriptome analysis of different potato cultivars provides insight into early blight disease caused by Alternaria solani

BackgroundEarly blight, caused by the necrotrophic fungal pathogen Alternaria solani, is an economically important disease affecting the tuber yield worldwide. The disease is mainly controlled by chemical plant protection agents. However, over-using these chemicals can lead to the evolution of resistant A. solani strains and is environmentally hazardous. Identifying genetic disease resistance factors is crucial for the sustainable management of early blight but little effort has been diverted in this direction. Therefore, we carried out transcriptome sequencing of the A. solani interaction with different potato cultivars with varying levels of early blight resistance to identify key host genes and pathways in a cultivar-specific manner.ResultsIn this study, we have captured transcriptomes from three different potato cultivars with varying susceptibility to A. solani, namely Magnum Bonum, Désirée, and Kuras, at 18 and 36 h post-infection. We identified many differentially expressed genes (DEGs) between these cultivars, and the number of DEGs increased with susceptibility and infection time. There were 649 transcripts commonly expressed between the potato cultivars and time points, of which 627 and 22 were up- and down-regulated, respectively. Interestingly, overall the up-regulated DEGs were twice in number as compared to down-regulated ones in all the potato cultivars and time points, except Kuras at 36 h post-inoculation. In general, transcription factor families WRKY, ERF, bHLH, MYB, and C2H2 were highly enriched DEGs, of which a significant number were up-regulated. The majority of the key transcripts involved in the jasmonic acid and ethylene biosynthesis pathways were highly up-regulated. Many transcripts involved in the mevalonate (MVA) pathway, isoprenyl-PP, and terpene biosynthesis were also up-regulated across the potato cultivars and time points. Compared to Magnum Bonum and Désirée, multiple components of the photosynthesis machinery, starch biosynthesis and degradation pathway were down-regulated in the most susceptible potato cultivar, Kuras.ConclusionsTranscriptome sequencing identified many differentially expressed genes and pathways, thereby contributing to the improved understanding of the interaction between the potato host and A. solani. The transcription factors identified are attractive targets for genetic modification to improve potato resistance against early blight. The results provide important insights into the molecular events at the early stages of disease development, help to shorten the knowledge gap, and support potato breeding programs for improved early blight disease resistance.

Elevated methylglyoxal levels inhibit tomato fruit ripening by preventing ethylene biosynthesis.

Methylglyoxal (MG), a toxic compound produced as a by-product of several cellular processes, such as respiration and photosynthesis, is well known for its deleterious effects, mainly through glycation of proteins during plant stress responses. However, very little is known about its impact on fruit ripening. Here, we found that MG levels are maintained at high levels in green tomato (Solanum lycopersicum L.) fruits and decline during fruit ripening despite a respiratory burst during this transition. We demonstrate that this decline is mainly mediated through a glutathione-dependent MG detoxification pathway and primarily catalyzed by a Glyoxalase I enzyme encoded by the SlGLYI4 gene. SlGLYI4 is a direct target of the MADS-box transcription factor RIPENING INHIBITOR (RIN), and its expression is induced during fruit ripening. Silencing of SlGLYI4 leads to drastic MG overaccumulation at ripening stages of transgenic fruits and interferes with the ripening process. MG most likely glycates and inhibits key enzymes such as methionine synthase and S-adenosyl methionine synthase in the ethylene biosynthesis pathway, thereby indirectly affecting fruit pigmentation and cell wall metabolism. MG overaccumulation in fruits of several nonripening or ripening-inhibited tomato mutants suggests that the tightly regulated MG detoxification process is crucial for normal ripening progression. Our results underpin a SlGLYI4-mediated regulatory mechanism by which MG detoxification controls fruit ripening in tomato.

Nitric oxide in co-ordination with nitrogen reverses cadmium-inhibited photosynthetic activity by interacting with ethylene synthesis, strengthening the antioxidant system, and nitrogen and sulfur assimilation in mustard (Brassica juncea L.)

Nitric oxide (NO) is a gaseous signaling molecule with known prominent roles in plant development and abiotic stress acclimation. This study reports that NO plus nitrogen (N) conspicuously alleviated cadmium (Cd)-inhibited photosynthetic activity by interacting with ethylene synthesis, and modifying the mechanisms of antioxidant enzymes, N and sulfur (S) assimilation in mustard (Brassica juncea L.) cv. Giriraj plants. The application of 100 µM sodium nitroprusside (SNP; NO donor) and 200 mg N kg−1 soil (as ammonium nitrate) to 200 mg Cd kg−1 soil-grown plants reduced oxidative stress (superoxide radical, hydrogen peroxide, and thiobarbituric acid reactive species content) and cell death through enhanced synthesis of metal chelators (non-protein thiols and phytochelatins) and limited Cd translocation. The reduced cellular ROS was also related to NO and N-mediated enhancement of S and N-assimilation, and antioxidants. The NO and N-mediated higher expression of psbA and psbB genes of D1 protein of PSII resulted into higher photosynthetic performance even under higher Cd regimes. Further, NO and N in the presence of aminoethoxyvinylglycine (AVG, ethylene biosynthesis inhibitor) under Cd stress showed reduced growth and photosynthetic attributes, with greater oxidative stress, substantiating ethylene involvement in NO and N-mediated reversal of Cd-inhibited photosynthesis. The principal component analysis showed a positive correlation between the treatment SNP + N + Cd and NO production, antioxidant enzymes, glutathione and metal chelators which resulted in higher N and S-assimilation, and better growth and photosynthetic capacity under Cd stress. The results indicate that NO-mediated alleviation of Cd toxicity and protection of photosynthetic activity were more conspicuous with N availability through the coordination with ethylene synthesis. The outcome of the study may be utilized in maintaining and managing hostile soils polluted with potentially toxic metals like Cd.

Insights into metabolite biosynthesis and regulation in rice immune signaling.

Plant metabolites are critical components of immune signaling pathways; however, how these small molecules contribute to plant immunity remains largely elusive. Emerging evidence demonstrates that the rice nucleotide-binding leucine-rich repeat receptor (NLR)-interacting proteins regulate the biosynthesis of ethylene, hydroxycinnamoylputrescines and diterpenoid phytoalexins to modulate plant immunity.

Extracellular self-DNA induced a PTI-related local defence against Rhizopus rot in postharvest peach fruit

The plant immune response against various pathogens relies on a convoluted recognition system based on perceiving exogenous or endogenous stimuli, such as pathogen- or damage-associated molecular patterns (PAMPs or DAMPs). Extracellular self-DNA (sDNA) is an established DAMP source, but the plant intracellular signaling mechanism after sDNA perception remains largely unclear. Here, we observed that peach fruit was more resistant to the fungus Rhizopus stolonifer after sDNA perception. We identified a complete MAPK cascade (MAPKKK1, MAPKK2 and MAPK1) that functions downstream of the FLS2-BAK1 receptor complex following the perception of sDNA-derived DAMPs by means of transcriptome sequencing. The results of yeast two-hybrid (Y2H) and glutathione S-transferase (GST) pull-down assays confirmed the protein interaction of FLS2 and BAK1; meanwhile, the interaction of MAPKKK1 and MAPKK2 and its downstream interaction of MAPKK2 and MAPK1 were both exhibited following the another Y2H results. Accordingly, MAPK1 interacted with 1-aminocyclopropane-1-carboxylate oxidase (ACO1), which was directly associated with increased ethylene production and upregulation of the transcription profile of ethylene synthesis-related genes (PpSAMDC, PpACS1 and PpACO1), ethylene receptors (ETRs and ERS1), ethylene-responsive transcription factors (ERFs) and three ethylene-inducible marker genes, PLANT DEFENSIN1.2 (PDF1.2), CHITINASE (CHI) and HOOKLESS1 (HLS1). Accordingly, the overexpression of MAPK1 enhanced the disease resistance of transgenic tomato against the fungus R. stolonifer and increased ethylene biosynthesis and ethylene signaling-related gene transcription. Taken together, our data provide insight into the putative mechanism underlying the recognition of sDNA components by the FLS2-BAK1 complex and its downstream events in the transduction of ethylene signaling by the MAPK cascade to mediate local resistance in postharvest peach fruit.

Comparative Transcriptome Analysis of the Differential Effects of Florpyrauxifen-Benzyl Treatment on Phytohormone Transduction between Florpyrauxifen-Benzyl-Resistant and -Susceptible Barnyard Grasses (Echinochloa crus-galli (L.) P. Beauv)

Echinochloa crus-galli (L.) P. Beauv (common name: barnyard grass) is a major weed in rice-growing areas and has evolved resistance to multiple herbicides. Florpyrauxifen-benzyl (trade name Rinskor) is a novel synthetic auxin herbicide that was approved in China in 2017 and is widely used in rice production to control resistant weeds, including barnyard grass. We identified a florpyrauxifen-benzyl-resistant E. crus-galli biotype with a resistance index (RI) of 11.89 using screen house herbicide experiments. To understand the phytotoxicity mechanisms of florpyrauxifen-benzyl, we used transcriptomics technologies to compare the gene expression profiles of florpyrauxifen-benzyl treatment on phytohormone transduction between florpyrauxifen-benzyl-resistant and -susceptible barnyard grasses (Echinochloa crus-galli (L.) P. Beauv). A total of 1810 DEGs were identified in the S comparison setting (FTS vs. UTS), and 915 DEGs were identified in the R comparison setting (FTR vs. UTR); 464 genes overlapped between the two comparison groups. Approximately sixty-nine hormone-related DEGs were detected after treatment with florpyrauxifen-benzyl in both R and S biotypes. At 24 h after florpyrauxifen-benzyl treatment, compared with the R biotype, the S biotype showed a stronger auxin response and higher expression of related genes involved in ethylene and abscisic acid biosynthesis and signal transduction. In addition, a brassinolide receptor gene was upregulated after florpyrauxifen-benzyl treatment and had higher expression in the S biotype than in the R biotype. This study is the first transcriptome analysis of the differential effects of florpyrauxifen-benzyl treatment between florpyrauxifen-benzyl-resistant and -susceptible E. crus-galli. It reflects the difference in phytohormone biosynthesis and signal transduction between R and S barnyard grasses in response to florpyrauxifen-benzyl treatment and will be helpful for understanding the phytotoxicity mechanisms of florpyrauxifen-benzyl.

Quality Improvement of Tomato Fruits by Preharvest Application of Chitosan Oligosaccharide

Chitosan oligosaccharide (COS), a degradation product of chitosan, is easily accessible, highly bioactive, non-toxic, and well-soluble in water. The effects of COS on the qualitative attributes of tomato fruits were investigated in the current study. COS was administered to tomato plants (Solanum lycopersicum cv. Ruixinghongniu) by foliar spray and root irrigation in alternate cycles at concentrations of 0.5 g·L−1 and 0.16 g·L−1, respectively. The experimental outcomes revealed that COS treatment promoted the coloring and softening of tomato fruits. Lycopene, vitamin C, fructose, and glucose levels increased by 49.0%, 25.4%, 30.2%, and 33.4%, respectively, in COS-treated ripe fruits compared to controls. The volatile metabolome showed that COS application also increased the release of ten volatiles correlated with consumer preference (1-penten-3-one, (E)-2-pentenal, (E)-3-hexen-1-ol, (E)-2-heptenal, 2-isobutylthiazole, phenylacetaldehyde, 2-phenylethanol, 6-methyl-5-hepten-2-one, 6-methyl-5-hepten-2-ol, and β-ionone), contributing to an improved tomato flavor. Moreover, increased transcript levels of genes participating in ethylene biosynthesis, perception, and response along with enhanced ethylene production were observed in COS-treated fruits, suggesting that COS may regulate tomato fruit quality via the ethylene pathway. Taken together, our results indicated that the pre-harvest application of COS could improve tomato fruit quality attributes.

Chromosome-level wild Hevea brasiliensis genome provides new tools for genomic-assisted breeding and valuable loci to elevate rubber yield.

The rubber tree (Hevea brasiliensis) is grown in tropical regions and is the major source of natural rubber. Using traditional breeding approaches, the latex yield has increased by sixfold in the last century. However, the underlying genetic basis of rubber yield improvement is largely unknown. Here, we present a high-quality, chromosome-level genome sequence of the wild rubber tree, the first report on selection signatures and a genome-wide association study (GWAS) of its yield traits. Population genomic analysis revealed a moderate population divergence between the Wickham clones and wild accessions. Interestingly, it is suggestive that H. brasiliensis and six relatives of the Hevea genus might belong to the same species. The selective sweep analysis found 361 obvious signatures in the domesticated clones associated with 245 genes. In a 15-year field trial, GWAS identified 155 marker-trait associations with latex yield, in which 326 candidate genes were found. Notably, six genes related to sugar transport and metabolism, and four genes related to ethylene biosynthesis and signalling are associated with latex yield. The homozygote frequencies of the causal nonsynonymous SNPs have been greatly increased under selection, which may have contributed to the fast latex yield improvement during the short domestication history. Our study provides insights into the genetic basis of the latex yield trait and has implications for genomic-assisted breeding by offering valuable resources in this new domesticated crop.

Phytohormone ethylene mediates oligogalacturonic acid-induced growth inhibition in tomato etiolated seedlings

Plant growth and immunity are tightly interconnected. Oligogalacturonic acids (OGs) are pectic fragments and have been well investigated in plant immunity as a damage-associated molecular pattern. However, little is known regarding how OGs affect plant growth. Here, we reveal that OGs inhibit the growth of intact etiolated seedling by using the horticultural crop tomato as a model. This inhibitory effect is partially suppressed by the action of ethylene biosynthesis inhibitors, or the gene silencing of SlACS2, an essential rate-limiting enzyme for ethylene biosynthesis, suggesting that SlACS2-mediated ethylene production promotes OG-induced growth inhibition. Furthermore, OGs treatment elevates the SlACS2 protein phosphorylation, and its decrease by the kinase inhibitor K252a partially rescue OG-induced growth inhibition, indicating that SlACS2 phosphorylation involves in OG-induced growth inhibition. Moreover, the mitogen-activated protein kinase SlMPK3 could be activated by OGs treatment and can directly phosphorylate SlACS2 in vitro, and the bimolecular fluorescence complementation combining with the yeast two-hybrid assay shows that SlMPK3 interacts with SlACS2, indicating that SlMPK3 may participate in modulating the OG-induced SlACS2 phosphorylation and growth inhibition. Our results reveal a regulatory mechanism at both the transcriptional and post-transcriptional levels by which OGs inhibit the growth of intact plant seedlings.

Ethylene Signal Is Involved in the Regulation of Anthocyanin Accumulation in Flesh of Postharvest Plums (Prunus salicina Lindl.)

Ethylene is positively correlated with the anthocyanin accumulation in postharvest plum fruit, but the regulation mechanism has not been fully clarified. In this work, the 'Friar' plum fruit under different storage temperatures (0, 10 and 25 °C) and treatments (100.0 μL L-1 ethylene and 1.0 μL L-1 1-MCP) were applied to study the relationship between anthocyanin accumulation and ethylene signal pathway. The fruits stored at 10 °C had higher ethylene production rate and more anthocyanin in flesh than those stored at 0 °C and 25 °C. Ten ethylene biosynthesis associated genes and forty-one ethylene signal transduction related genes were obtained from the previous transcriptome data. Among them, the expression levels of ethylene biosynthesis associated genes (PsACS1, PsACS4 and PsACO1), and ethylene signal transduction related genes (PsERS1s, PsETR2, PsERF1a, and PsERF12) were markedly higher in the fruits stored at 10 °C than those at 0 °C and 25 °C. Exogenous ethylene treatment enhanced while 1-MCP treatment inhibited the anthocyanin accumulation in the flesh under storage at 10 °C. In addition, exogenous ethylene treatment markedly increased the expression levels of PsACS1, PsACS4, PsACO1, PsETR2, PsERF1a, and PsERF12 in the flesh once it turning red, as well as the anthocyanin biosynthesis related genes (PsPAL, PsCHS, PsF3H, PsDRF, PsANS, PsUFGT and PsMYB10), whereas 1-MCP treatment manifested the contrary effects. Correlation analysis indicated that there was a significant positive correlation between genes expression related to ethylene signal pathway and anthocyanin biosynthesis, except for PsERF11. In conclusion, ethylene signal pathway is involved in the flesh reddening by up-regulating the anthocyanin biosynthesis related genes.

Integrating Transcriptomics and Hormones Dynamics Reveal Seed Germination and Emergence Process in Polygonatum cyrtonema Hua.

Polygonatum cyrtonema Hua is a traditional Chinese herb propagated using rhizomes, and excessive demand for seedlings and quality deterioration caused by rhizome propagation has highlighted that seed propagation may be an ideal solution to address these issues. However, the molecular mechanisms involved in P. cyrtonema Hua seed germination and emergence stages are not well understood. Therefore, in the present study, we performed transcriptomics combined with hormone dynamics during different seed germination stages, and 54,178 unigenes with an average length of 1390.38 bp (N50 = 1847 bp) were generated. Significant transcriptomic changes were related to plant hormone signal transduction and the starch and carbohydrate pathways. Genes related to ABA(abscisic acid), IAA(Indole acetic acid), and JA(Jasmonic acid) signaling, were downregulated, whereas genes related to ethylene, BR(brassinolide), CTK(Cytokinin), and SA(salicylic acid) biosynthesis and signaling were activated during the germination process. Interestingly, GA biosynthesis- and signaling-related genes were induced during the germination stage but decreased in the emergence stage. In addition, seed germination significantly upregulated the expression of genes associated with starch and sucrose metabolism. Notably, raffinose biosynthesis-related genes were induced, especially during the emergence stage. In total, 1171 transcription factor (TF) genes were found to be differentially expressed. Our results provide new insights into the mechanisms underlying P. cyrtonema Hua seed germination and emergence processes and further research for molecular breeding.

Suppression of the target of rapamycin kinase accelerates tomato fruit ripening through reprogramming the transcription profile and promoting ethylene biosynthesis.

Tomato fruit ripening is a unique process of nutritional and energy metabolism. Target of rapamycin (TOR), a conserved serine/threonine protein kinase in eukaryotes, controls cell growth and metabolism by integrating nutrient, energy, and hormone signals. However, it remains unclear whether TOR participates in the modulation of tomato fruit ripening. Here, we showed that the manipulation of SlTOR by chemical or genetic methods greatly alters the process of tomato fruit maturation. Expression pattern analysis revealed that the transcripts of SlTOR declined as fruit ripening progressed. Moreover, suppression of SlTOR by TOR inhibitor AZD8055 or knock down of its transcripts by inducible RNA interference, accelerated fruit ripening, and led to overall effects on fruit maturity, including changes in colour and metabolism, fruit softening, and expression of ripening-related genes. Genome-wide transcription analysis indicated that silencing SlTOR reprogrammed the transcript profile associated with ripening, including cell wall and phytohormone pathways, elevated the expression of ethylene biosynthetic genes, and further promoted ethylene production. In contrast, the ethylene action inhibitor 1-MCP efficiently blocked fruit maturation, even following SlTOR inhibition. These results suggest that accelerated fruit ripening caused by SlTOR inhibition depends on ethylene, and that SlTOR may function as a regulator in ethylene metabolism.

CRISPR/Cas9-mediated SNAC9 mutants reveal the positive regulation of tomato ripening by SNAC9 and the mechanism of carotenoid metabolism regulation.

NAC transcriptional regulators are crucial for tomato ripening. Virus-induced gene silencing (VIGS) of SNAC9 (SlNAC19, Gene ID: 101248665) affects tomato ripening, and SNAC9 is involved in ethylene and abscisic acid (ABA) metabolic pathways. However, the function of SNAC9 in pigment metabolism in tomatoes remains unclear. This work seeks to discover the mechanism of SNAC9 involvement in pigment metabolism during tomato ripening by establishing a SNAC9 knockout model using CRISPR/Cas9 technology. The results indicated that fruit ripening was delayed in knockout (KO) mutants, and SNAC9 mutation significantly affected carotenoid metabolism. The chlorophyll (Chl) degradation rate, total carotenoid content, and lycopene content decreased significantly in the mutants. The transformation rate of chloroplasts to chromoplasts in mutants was slower, which was related to the carotenoid content. Furthermore, SNAC9 changed the expression of critical genes (PSY1, PDS, CRTISO, Z-ISO, SGR1, DXS2, LCYE, LCYB, and CrtR-b2) involved in pigment metabolism in tomato ripening. SNAC9 knockout also altered the expression levels of critical genes involved in the biosynthesis of ethylene and ABA. Accordingly, SNAC9 regulated carotenoid metabolism by directly regulating PSY1, DXS2, SGR1, and CrtR-b2. This research provides a foundation for developing the tomato ripening network and precise tomato ripening regulation.

Transcriptomic and physiological analysis reveal phytohormone and phenylpropanoid biosynthesis in root of Cynanchum auriculatum

Baishouwu (Cynanchum auriculatum), a medicinal and food dual-use plant, has been cultivated for centuries and is favored by consumers. C. auriculatum tuberous roots contain enormous amounts of flavonoids, lignin, and other nutrients. However, the developmental characteristics and phenylpropanoid metabolic mechanism in C. auriculatum have not been clarified. Here, the phenotypes of C. auriculatum tuberous roots at three stages of developmental were observed, compared with root forming stage (S1), there were significant morphological differences at root expanding stage (S2) and harvest stage (S3). Through next-generation sequencing (NGS) on Illumina HiSeq2500 platform, nine transcriptomic libraries were constructed for transcriptomic analysis. A total of 28,926 DEGs were identified during the development of C. auriculatum tuberous root, and many DEGs were enriched in GO terms/ KEGG pathways of ‘phytohormone signal transduction’ and ‘phenylpropanoid biosynthesis’. The analysis of phytohormone content and gene expression revealed that auxin and cytokinin acted in concert to regulate C. auriculatum tuberous root development, while the biosynthesis and signaling of ethylene were inhibited. Phloroglucinol staining results showed that lignified cells were mainly distributed in the central xylem at S1, followed by ring-like structure formation at S2, and finally formed the connecting rays between the xylem and the phloem at S3. Lignin content increased at S2 and then decreased at S3, and the expression of lignin synthesis genes also presented a similar trend. Total flavonoids content showed a gradually increasing trend, and the expression of flavonoid synthesis genes was also gradually up-regulated. The flavonoid synthesis pathway was enhanced by reducing the activity of key enzymes in lignin synthesis in C. auriculatum. This study provided a basis for the developmental mechanism of C. auriculatum and the further utilization of C. auriculatum tuberous roots.