ABA Biosynthesis Research Articles

A Comprehensive Evaluation of Salt Tolerance in Tomato (Var. Ailsa Craig): Responses of Physiological and Transcriptional Changes in RBOH's and ABA Biosynthesis and Signalling Genes.

Salinity is a ubiquitous stressor, depleting osmotic potential and affecting the tomato seedlings’ development and productivity. Considering this critical concern, we explored the salinity response in tomato seedlings by evaluating them under progressive salt stress duration (0, 3, 6, and 12 days). Intriguingly, besides the adverse effect of salt stress on tomato growth the findings exhibited a significant role of tomato antioxidative system, RBOH genes, ABA biosynthesis, and signaling transcription factor for establishing tolerance to salinity stress. For instance, the activities of enzymatic and non-enzymatic antioxidants continued to incline positively with the increased levels of reactive oxygen species (O2•−, H2O2), MDA, and cellular damage, suggesting the scavenging capacity of tomato seedlings against salt stress. Notably, the RBOH transcription factors activated the hydrogen peroxide-mediated signalling pathway that induced the detoxification mechanisms in tomato seedlings. Consequently, the increased gene expression of antioxidant enzymes and the corresponding ratio of non-enzymatic antioxidants AsA-GSH suggested the modulation of antioxidants to survive the salt-induced oxidative stress. In addition, the endogenous ABA level was enhanced under salinity stress, indicating higher ABA biosynthesis and signalling gene expression. Subsequently, the upregulated transcript abundance of ABA biosynthesis and signalling-related genes suggested the ABA-mediated capacity of tomato seedlings to regulate homeostasis under salt stress. The current findings have revealed fascinating responses of the tomato to survive the salt stress periods, in order to improve the abiotic stress tolerance in tomato.

Overexpression of ZmPCK2, a phosphoenolpyruvate carboxykinase gene from maize confers enhanced tolerance to water deficit stress in rice

Water deficit is one of the major abiotic stresses that limit plant growth and global crop yields. Phosphoenolpyruvate carboxykinase (PCK) plays important roles in regulating plant growth and development, but its role in water-deficit stress remains elusive. In this study, we found that overexpression of ZmPCK2 significantly enhanced the water-deficit tolerance of transgenic rice. The expression level of ZmPCK2 was strongly induced by PEG and ABA treatments. Overexpression of ZmPCK2 in rice increased stomatal closure and water saving by regulating malate metabolism under water-deficit conditions. Moreover, the expression of ZmPCK2 in rice up-regulated ABA biosynthesis and responsive genes under water-deficit stress, and ZmPCK2 transgenic rice showed hypersensitive to exogenous ABA at germination stage, suggesting that ZmPCK2 may be involved in ABA signalling pathway. Under water-deficit stress, the ZmPCK2 transgenic rice showed higher antioxidant enzyme activities and lower accumulation of reactive oxygen species (ROS) compared with non-transgenic (NT) plants, resulting in less oxidative damage. Taken together, we suggest that ZmPCK2 plays multiple roles in response to water-deficit stress by enhancing ABA signalling pathway, regulating malate metabolism, promoting stomatal closure and further activating the ROS-scavenging system.

Characterization of wavy root 1, an agravitropism allele, reveals the functions of OsPIN2 in fine regulation of auxin transport and distribution and in ABA biosynthesis and response in rice (Oryza sativa L.)

Root system architecture is influenced by gravity. How the root senses gravity and directs its orientation, so-called gravitropism, is not only a fundamental question in plant biology but also theoretically important for genetic improvement of crop root architecture. However, the mechanism has not been elucidated in most crops. We characterized a rice agravitropism allele, wavy root 1 (war1), a loss-of-function allele in OsPIN2, which encodes an auxin efflux transporter. With loss of OsPIN2 function, war1 leads to altered root system architecture including wavy root, larger root distribution angle, and shallower root system due to the loss of gravitropic perception in root tips. In the war1 mutant, polar auxin transport was disrupted in the root tip, leading to abnormal auxin levels and disturbed auxin transport and distribution in columella cells. Amyloplast sedimentation, an important process in gravitropic sensing, was also decreased in root tip columella cells. The results indicated that OsPIN2 controls gravitropism by finely regulating auxin transport, distribution and levels, and amyloplast sedimentation in root tips. We identified a novel role of OsPIN2 in regulating ABA biosynthesis and response pathways. Loss of OsPIN2 function in the war1 resulted in increased sensitivity to ABA in seed germination, increased ABA level, changes in ABA-associated genes in roots, and decreased drought tolerance in the seedlings. These results suggest that the auxin transporter OsPIN2 not only modulates auxin transport to control root gravitropism, but also functions in ABA signaling to affect seed germination and root development, probably by mediating crosstalk between auxin and ABA pathways.

New insights into the role of cyanide in the promotion of seed germination in tomato

BackgroundCyanide is a natural metabolite that exists widely in plants, and it is speculated to be involved in the regulation of various growth and development processes of plants in addition to being regarded as toxic waste. Previous studies have shown that exogenous cyanide treatment helps to improve seed germination, but the mechanism is still unclear. In this study, tomato (Solanum lycopersicum cv. Alisa Craig) was used as the material, and the effects of cyanide pretreatment at different concentrations on tomato seed germination were investigated.ResultsThe results showed that exogenous application of a lower concentration of cyanide (10 μmol/L KCN) for 12 h strongly increased the tomato seed germination rate. RNA-Seq showed that compared with the control, a total of 15,418 differentially expressed genes (P<0.05) were obtained after pretreatment with KCN for 12 h, and in the next 12 h, a total of 13,425 differentially expressed genes (P<0.05) were regulated. GO and KEGG analyses demonstrated that exogenous KCN pretreatment was involved in regulating the expression (mainly downregulation) of seed storage proteins, thereby accelerating the degradation of stored proteins for seed germination. In addition, KCN pretreatment was also involved in stimulating glycolysis, the TCA cycle and oxidative phosphorylation. Notably, it is shown that KCN acted on the regulation of plant hormone biosynthesis and perception, i.e., down-regulated the gene expression of ABA biosynthesis and signal transduction, but up-regulated the expression of genes related to GA biosynthesis and response. Consistent with this, plant hormone measurements confirmed that the levels of ABA were reduced, but GA levels were induced after pretreatment with KCN.ConclusionThese findings provide new insights into the regulation of seed germination by cyanide, that is cyanide-mediated seed germination occurs in a time- and dose-dependent manner, and is related to the mobilization of energy metabolism and the regulation of some plant hormone signals.

Poly-\u03b3-glutamic acid enhanced the drought resistance of maize by improving photosynthesis and affecting the rhizosphere microbial community

BackgroundCompared with other abiotic stresses, drought stress causes serious crop yield reductions. Poly-γ-glutamic acid (γ-PGA), as an environmentally friendly biomacromolecule, plays an important role in plant growth and regulation.ResultsIn this project, the effect of exogenous application of γ-PGA on drought tolerance of maize (Zea mays. L) and its mechanism were studied. Drought dramatically inhibited the growth and development of maize, but the exogenous application of γ-PGA significantly increased the dry weight of maize, the contents of ABA, soluble sugar, proline, and chlorophyll, and the photosynthetic rate under severe drought stress. RNA-seq data showed that γ-PGA may enhance drought resistance in maize by affecting the expression of ABA biosynthesis, signal transduction, and photosynthesis-related genes and other stress-responsive genes, which was also confirmed by RT–PCR and promoter motif analysis. In addition, diversity and structure analysis of the rhizosphere soil bacterial community demonstrated that γ-PGA enriched plant growth promoting bacteria such as Actinobacteria, Chloroflexi, Firmicutes, Alphaproteobacteria and Deltaproteobacteria. Moreover, γ-PGA significantly improved root development, urease activity and the ABA contents of maize rhizospheric soil under drought stress. This study emphasized the possibility of using γ-PGA to improve crop drought resistance and the soil environment under drought conditions and revealed its preliminary mechanism.ConclusionsExogenous application of poly-γ-glutamic acid could significantly enhance the drought resistance of maize by improving photosynthesis, and root development and affecting the rhizosphere microbial community.

Use of Micrografting to Study the Role Played by Peptide Signals in ABA Biosynthesis.

Plants survive by deploying appropriate stress responses under rapidly changing environmental conditions. Vascular plants transmit environmental information among distant organs. Long-distance signaling plays a crucial role in plant adaptation and subsequent survival under severe environmental conditions. In model plants, the micrografting method has recently emerged as an important method to elucidate tissue-to-tissue communication via hormones, RNAs, and peptides. In this chapter, I describe a micrografting method for Arabidopsis thaliana to graft shoots onto roots of plants with different genotypes. This grafting method may facilitate further research investigating how vascular plants integrate environmental information among distant organs via long-distance signaling.

Ghmyb102 Promotes Drought Resistance in Cotton (Gossypium Hirsutum L.) by Regulating Drought-Responsive Genes and Aba Biosynthesis

Ghmyb102 Promotes Drought Resistance in Cotton (Gossypium Hirsutum L.) by Regulating Drought-Responsive Genes and Aba Biosynthesis

DELAY OF GERMINATION 1 (DOG1) regulates dormancy in dimorphic seeds of Xanthium strumarium.

Seed dormancy ensures plant survival but many mechanisms remain unclear. A high-throughput RNA-seq analysis investigated the mechanisms involved in the establishment of dormancy in dimorphic seeds of Xanthium strumarium (L.) developing in one single burr. Results showed that DOG1 , the main dormancy gene in Arabidopsis thaliana L., was over-represented in the dormant seed leading to the formation of two seeds with different cell wall properties. Less expression of DME /EMB1649 , UBP26 , EMF2, MOM, SNL2, and AGO4 in the non-dormant seed was observed, which function in the chromatin remodelling of dormancy-associated genes through DNA methylation. However, higher levels of ATXR7 /SDG25, ELF6 , and JMJ16/PKDM7D in the non-dormant seed that act at the level of histone demethylation and activate germination were found. Dramatically lower expression in the splicing factors SUA, PWI , and FY in non-dormant seed may indicate that variation in RNA splicing for ABA sensitivity and transcriptional elongation control of DOG1 is of importance for inducing seed dormancy. Seed size and germination may be influenced by respiratory factors, and alterations in ABA content and auxin distribution and responses. TOR (a serine/threonine-protein kinase) is likely at the centre of a regulatory hub controlling seed metabolism, maturation, and germination. Over-representation of the respiration-associated genes (ACO3 , PEPC3 , and D2HGDH ) was detected in non-dormant seed, suggesting differential energy supplies in the two seeds. Degradation of ABA biosynthesis and/or proper auxin signalling in the large seed may control germinability, and suppression of endoreduplication in the small seed may be a mechanism for cell differentiation and cell size determination.

Transcriptomic Insights on the Preventive Action of Apple (cv Granny Smith) Skin Wounding on Superficial Scald Development.

Superficial scald is a post-harvest chilling storage injury leading to browning of the surface of the susceptible cv Granny Smith apples. Wounding of skins has been reported to play a preventive role on scald development however its underlying molecular factors are unknown. We have artificially wounded the epidermal and sub-epidermal layers of apple skins consistently obtaining the prevention of superficial scald in the surroundings of the wounds during two independent vintages. Time course RNA-Seq analyses of the transcriptional changes in wounded versus unwounded skins revealed that two transcriptional waves occurred. An early wave included genes up-regulated by wounding already after 6 h, highlighting a specific transcriptional rearrangement of genes connected to the biosynthesis and signalling of JA, ethylene and ABA. A later transcriptional wave, occurring after three months of cold storage, included genes up-regulated exclusively in unwounded skins and was prevented from its occurrence in wounded skins. A significant portion of these genes was related to decay of tissues and to the senescence hormones ABA, JA and ethylene. Such changes suggest a wound-inducible reversed hormonal balance during post-harvest storage which may explain the local inhibition of scald in wounded tissues, an aspect that will need further studies for its mechanistic explanation.

Silencing an E3 Ubiquitin Ligase Gene OsJMJ715 Enhances the Resistance of Rice to a Piercing-Sucking Herbivore by Activating ABA and JA Signaling Pathways.

The RING-type E3 ubiquitin ligases play an important role in plant growth, development, and defense responses to abiotic stresses and pathogens. However, their roles in the resistance of plants to herbivorous insects remain largely unknown. In this study, we isolated the rice gene OsJMJ715, which encodes a RING-domain containing protein, and investigated its role in rice resistance to brown planthopper (BPH, Nilaparvata lugens). OsJMJ715 is a nucleus-localized E3 ligase whose mRNA levels were upregulated by the infestation of gravid BPH females, mechanical wounding, and treatment with JA or ABA. Silencing OsJMJ715 enhanced BPH-elicited levels of ABA, JA, and JA-Ile as well as the amount of callose deposition in plants, which in turn increased the resistance of rice to BPH by reducing the feeding of BPH and the hatching rate of BPH eggs. These findings suggest that OsJMJ715 negative regulates the BPH-induced biosynthesis of ABA, JA, and JA-Ile and that BPH benefits by enhancing the expression of OsJMJ715.

The bHLH transcription factor AhbHLH112 improves the drought tolerance of peanut

BackgroundBasic helix-loop-helix (bHLH) transcription factors (TFs) are one of the largest gene families in plants. They regulate gene expression through interactions with specific motifs in target genes. bHLH TFs are not only universally involved in plant growth but also play an important role in plant responses to abiotic stress. However, most members of this family have not been functionally characterized.ResultsHere, we characterized the function of a bHLH TF in the peanut, AhHLH112, in response to drought stress. AhHLH112 is localized in the nucleus and it was induced by drought stress. The overexpression of this gene improves the drought tolerance of transgenic plants both in seedling and adult stages. Compared to wild-type plants, the transgenic plants accumulated less reactive oxygen species (ROS), accompanied by increased activity and transcript levels of antioxidant enzymes (superoxide dismutase, peroxidase and catalase). In addition, the WT plants demonstrated higher MDA concentration levels and higher water loss rate than the transgenic plants under drought treatment. The Yeast one-hybrid result also demonstrates that AhbHLH112 directly and specifically binds to and activates the promoter of the peroxidase (POD) gene. Besides, overexpression of AhHLH112 improved ABA level under drought condition, and elevated the expression of genes associated with ABA biosynthesis and ABA responding, including AtNCED3 and AtRD29A.ConclusionsDrawing on the results of our experiments, we propose that, by improving ROS-scavenging ability, at least in part through the regulation of POD -mediated H2O2 homeostasis, and possibly participates in ABA-dependent stress-responding pathway, AhbHLH112 acts as a positive factor in drought stress tolerance.

Unique features of the m6A methylome and its response to drought stress in sea buckthorn (Hippophae rhamnoides Linn.)

ABSTRACT In plants, recent studies have revealed that N6-methyladenosine (m6A) methylation of mRNA has potential regulatory functions of this mRNA modification in many biological processes. m6A methyltransferase, m6A demethylase and m6A-binding proteins can cause differential phenotypes, indicating that m6A may have critical roles in the plant. In this study, we depicted the m6A map of sea buckthorn (Hippophae rhamnoides Linn.) transcriptome. Similar to A. thaliana, m6A sites of sea buckthorn transcriptome is significantly enriched around the stop codon and within 3ʹ-untranslated regions (3ʹUTR). Gene ontology analysis shows that the m6A modification genes are associated with metabolic biosynthesis. In addition, we identified 13,287 different m6A peaks (DMPs) between leaf under drought (TR) and control (CK) treatment. It reveals that m6A has a high level of conservation and has a positive correlation with mRNA abundance in plants. GO and KEGG enrichment results showed that DMP modification DEGs in TR were particularly associated with ABA biosynthesis. Interestingly, our results showed three m6A demethylase (HrALKBH10B, HrALKBH10C and HrALKBH10D) genes were significantly increased following drought stress, which indicated that it may contributed the decreased m6A levels. This exhaustive m6A map provides a basis and resource for the further functional study of mRNA m6A modification in abiotic stress.

Ipa1 improves rice drought tolerance at seedling stage mainly through activating abscisic acid pathway.

KEY MESSAGE: ipa1 enhances rice drought tolerance mainly through activating the ABA pathway. It endows rice seedlings with a more developed root system, smaller leaf stomata aperture, and enhanced carbon metabolism. Drought is a major abiotic stress to crop production. IPA1 (IDEAL PLANT ARCHITECTURE 1)/OsSPL14 encodes a transcription factor and has been reported to function in both rice ideal plant architecture and biotic resistance. Here, with a pair of IPA1 and ipa1-NILs (Near Iso-genic Lines), we found that ipa1 could significantly improve rice drought tolerance at seedling stage. The ipa1 plants had a better-developed root system and smaller leaf stomatal aperture. Analysis of carbon-nitrogen metabolism-associated enzyme activity, gene expression, and metabolic profile indicated that ipa1 could tip the carbon-nitrogen metabolism balance towards an increased carbon metabolism pattern. In both the control and PEG-treated conditions, ABA content in the ipa1 seedlings was significantly higher than that in the IPA1 seedlings. Expression of the ABA biosynthesis genes was detected to be up-regulated, whereas the expression of ABA catabolism genes was down-regulated in the ipa1 seedlings. In addition, based on yeast one-hybrid assay and dual-luciferase assay, IPA1 was found to directly activate the promoter activity of OsHOX12, a transcription factor promoting ABA biosynthesis, and OsNAC52, a positive regulator of the ABA pathway. The expression of OsHOX12 and OsNAC52 was significantly up-regulated in the ipa1 plants. Combined with the previous studies, our results suggested that ipa1 could improve rice seedling drought tolerance mainly through activating the ABA pathway and that regulation of the ipa1-mediated ABA pathway will be an important strategy for improving drought resistance of rice.

Characterization of Phytochrome-Interacting Factor Genes in Pepper and Functional Analysis of CaPIF8 in Cold and Salt Stress.

As a subfamily of basic helix-loop-helix (bHLH) transcription factors, phytochrome-interacting factors (PIFs) participate in regulating light-dependent growth and development of plants. However, limited information is available about PIFs in pepper. In the present study, we identified six pepper PIF genes using bioinformatics-based methods. Phylogenetic analysis revealed that the PIFs from pepper and some other plants could be divided into three distinct groups. Motif analysis revealed the presence of many conserved motifs, which is consistent with the classification of PIF proteins. Gene structure analysis suggested that the CaPIF genes have five to seven introns, exhibiting a relatively more stable intron number than other plants such as rice, maize, and tomato. Expression analysis showed that CaPIF8 was up-regulated by cold and salt treatments. CaPIF8-silenced pepper plants obtained by virus-induced gene silencing (VIGS) exhibited higher sensitivity to cold and salt stress, with an obvious increase in relative electrolyte leakage (REL) and variations in the expression of stress-related genes. Further stress tolerance assays revealed that CaPIF8 plays different regulatory roles in cold and salt stress response by promoting the expression of the CBF1 gene and ABA biosynthesis genes, respectively. Our results reveal the key roles of CaPIF8 in cold and salt tolerance of pepper, and lay a solid foundation for clarifying the biological roles of PIFs in pepper and other plants.

Transcriptomic and Metabolic Analyses Reveal the Mechanism of Ethylene Production in Stony Hard Peach Fruit during Cold Storage.

Stony hard (SH) peach (Prunus persica L. Batsch) fruit does not release ethylene and has very firm and crisp flesh at ripening, both on- and off-tree. Long-term cold storage can induce ethylene production and a serious risk of chilling injury in SH peach fruit; however, the regulatory mechanism underlying ethylene production in stony hard peach is relatively unclear. In this study, we analyzed the phytohormone levels, fruit firmness, transcriptome, and lipidome changes in SH peach ‘Zhongtao 9’ (CP9) during cold storage (4 °C). The expression level of the ethylene biosynthesis gene PpACS1 and the content of ethylene in SH peach fruit were found to be upregulated during cold storage. A peak in ABA release was observed before the release of ethylene and the genes involved in ABA biosynthesis and degradation, such as zeaxanthin epoxidase (ZEP) and 8’-hydroxylase (CYP707A) genes, were specifically induced in response to low temperatures. Fruit firmness decreased fairly slowly during the first 20 d of refrigeration, followed by a sharp decline. Furthermore, the expression level of genes encoding cell wall metabolic enzymes, such as polygalacturonase, pectin methylesterase, expansin, galactosidase, and β-galactosidase, were upregulated only upon refrigeration, as correlated with the decrease in fruit firmness. Lipids belonging to 23 sub-classes underwent differential rearrangement during cold storage, especially ceramide (Cer), monoglycosylceramide (CerG1), phosphatidic acid (PA), and diacyglyceride (DG), which may eventually lead to ethylene production. Exogenous PC treatment provoked a higher rate of ethylene production. We suspected that the abnormal metabolism of ABA and cell membrane lipids promotes the production of ethylene under low temperature conditions, causing the fruit to soften. In addition, ERF transcription factors also play an important role in regulating lipid, hormone, and cell wall metabolism during long-term cold storage. Overall, the results of this study give us a deeper understanding of the molecular mechanism of ethylene biosynthesis during the postharvest storage of SH peach fruit under low-temperature conditions.

Maize WRKY Transcription Factor ZmWRKY79 Positively Regulates Drought Tolerance through Elevating ABA Biosynthesis.

Drought stress causes heavy damages to crop growth and productivity under global climatic changes. Transcription factors have been extensively studied in many crops to play important roles in plant growth and defense. However, there is a scarcity of studies regarding WRKY transcription factors regulating drought responses in maize crops. Previously, ZmWRKY79 was identified as the regulator of maize phytoalexin biosynthesis with inducible expression under different elicitation. Here, we elucidated the function of ZmWRKY79 in drought stress through regulating ABA biosynthesis. The overexpression of ZmWRKY79 in Arabidopsis improved the survival rate under drought stress, which was accompanied by more lateral roots, lower stomatal aperture, and water loss. ROS scavenging was also boosted by ZmWRKY79 to result in less H2O2 and MDA accumulation and increased antioxidant enzyme activities. Further analysis detected more ABA production in ZmWRKY79 overexpression lines under drought stress, which was consistent with up-regulated ABA biosynthetic gene expression by RNA-seq analysis. ZmWRKY79 was observed to target ZmAAO3 genes in maize protoplast through acting on the specific W-boxes of the corresponding gene promoters. Virus-induced gene silencing of ZmWRKY79 in maize resulted in compromised drought tolerance with more H2O2 accumulation and weaker root system architecture. Together, this study substantiates the role of ZmWRKY79 in the drought-tolerance mechanism through regulating ABA biosynthesis, suggesting its broad functions not only as the regulator in phytoalexin biosynthesis against pathogen infection but also playing the positive role in abiotic stress response, which provides a WRKY candidate gene to improve drought tolerance for maize and other crop plants.

Chromosome-scale assembly of the Dendrobium chrysotoxum genome enhances the understanding of orchid evolution

As one of the largest families of angiosperms, the Orchidaceae family is diverse. Dendrobium represents the second largest genus of the Orchidaceae. However, an assembled high-quality genome of species in this genus is lacking. Here, we report a chromosome-scale reference genome of Dendrobium chrysotoxum, an important ornamental and medicinal orchid species. The assembled genome size of D. chrysotoxum was 1.37 Gb, with a contig N50 value of 1.54 Mb. Of the sequences, 95.75% were anchored to 19 pseudochromosomes. There were 30,044 genes predicted in the D. chrysotoxum genome. Two whole-genome polyploidization events occurred in D. chrysotoxum. In terms of the second event, whole-genome duplication (WGD) was also found to have occurred in other Orchidaceae members, which diverged mainly via gene loss immediately after the WGD event occurred; the first duplication was found to have occurred in most monocots (tau event). We identified sugar transporter (SWEET) gene family expansion, which might be related to the abundant medicinal compounds and fleshy stems of D. chrysotoxum. MADS-box genes were identified in D. chrysotoxum, as well as members of TPS and Hsp90 gene families, which are associated with resistance, which may contribute to the adaptive evolution of orchids. We also investigated the interplay among carotenoid, ABA, and ethylene biosynthesis in D. chrysotoxum to elucidate the regulatory mechanisms of the short flowering period of orchids with yellow flowers. The reference D. chrysotoxum genome will provide important insights for further research on medicinal active ingredients and breeding and enhances the understanding of orchid evolution.

The Complexity of Modulating Anthocyanin Biosynthesis Pathway by Deficit Irrigation in Table Grapes.

Deficit irrigation (DI) is an irrigation scheduling technique that is used in grapes to improve red color development; however, results are not always satisfactory in table grapes. The red color in grapes is mainly due to the plant pigment anthocyanin. In the present study, the anthocyanin biosynthesis in Scarlet Royal grapes (Vitis vinifera L.) grown in the San Joaquin and Coachella Valleys, and subjected to two different DI strategies was investigated. The objective of this study was to identify potential regulatory factors that may lead to potential treatments to improve red color in table grapes, especially under warm climate conditions. In both locations, DI induced the expression of several genes involved in three major pathways that control the red color in table grapes: anthocyanin biosynthesis, hormone biosynthesis, and antioxidant system. DI at veraison induced anthocyanin accumulation and enhanced red color in berries at harvest time. However, anthocyanin accumulation was lower at the Coachella Valley compared to the San Joaquin Valley. The lower level of anthocyanin was associated with lower expression of critical genes involved in anthocyanin biosynthesis, such as flavonoid-3-O-glucosyltransferase (UFGT), myb-related regulatory gene (R2R3-MYB) (MYBA1), basic helix-loop-helix (bHLH) (MYCA1) and the tryptophan-aspartic acid repeat (WDR or WD40) proteins (WDR1). Further, gene expression analysis revealed the association of ABA biosynthesis gene 9-cis-epoxycarotenoid dioxygenase (NCED1), 1-aminocyclopropane-1-carboxylic acid oxidase (ACO3), and the gibberellic acid (GA) catabolic gene GA2 oxidase (GA2ox1) in the induction of anthocyanin biosynthesis. An increase in the chalcone synthase gene (CHS2) was observed in response to DI treatments in both sites. However, CHS2 expression was higher in Coachella Valley after ending the DI treatment, suggesting the involvement of environmental stress in elevating its transcripts. This data was also supported by the lower level of antioxidant gene expression and enzyme activities in the Coachella Valley compared to the San Joaquin Valley. The present data suggested that the lack of grape red coloration could partially be due to the lower level of antioxidant activities resulting in accelerated anthocyanin degradation and impaired anthocyanin biosynthesis. It seems that under challenging warmer conditions, several factors are required to optimize anthocyanin accumulation via DI, including an active antioxidant system, proper light perception, and hormonal balance.

Transcriptomics of Improved Fruit Retention by Hexanal in 'Honeycrisp' Reveals Hormonal Crosstalk and Reduced Cell Wall Degradation in the Fruit Abscission Zone.

Apples (Malus domestica Borkh) are prone to preharvest fruit drop, which is more pronounced in ‘Honeycrisp’. Hexanal is known to improve fruit retention in several economically important crops. The effects of hexanal on the fruit retention of ‘Honeycrisp’ apples were assessed using physiological, biochemical, and transcriptomic approaches. Fruit retention and fruit firmness were significantly improved by hexanal, while sugars and fresh weight did not show a significant change in response to hexanal treatment. At commercial maturity, abscisic acid and melatonin levels were significantly lower in the treated fruit abscission zone (FAZ) compared to control. At this stage, a total of 726 differentially expressed genes (DEGs) were identified between treated and control FAZ. Functional classification of the DEGs showed that hexanal downregulated ethylene biosynthesis genes, such as S-adenosylmethionine synthase (SAM2) and 1-aminocyclopropane-1-carboxylic acid oxidases (ACO3, ACO4, and ACO4-like), while it upregulated the receptor genes ETR2 and ERS1. Genes related to ABA biosynthesis (FDPS and CLE25) were also downregulated. On the contrary, key genes involved in gibberellic acid biosynthesis (GA20OX-like and KO) were upregulated. Further, hexanal downregulated the expression of genes related to cell wall degrading enzymes, such as polygalacturonase (PG1), glucanases (endo-β-1,4-glucanase), and expansins (EXPA1-like, EXPA6, EXPA8, EXPA10-like, EXPA16-like). Our findings reveal that hexanal reduced the sensitivity of FAZ cells to ethylene and ABA. Simultaneously, hexanal maintained the cell wall integrity of FAZ cells by regulating genes involved in cell wall modifications. Thus, delayed fruit abscission by hexanal is most likely achieved by minimizing ABA through an ethylene-dependent mechanism.

OsMADS23 phosphorylated by SAPK9 confers drought and salt tolerance by regulating ABA biosynthesis in rice.

Some of MADS-box transcription factors (TFs) have been shown to play essential roles in the adaptation of plant to abiotic stress. Still, the mechanisms that MADS-box proteins regulate plant stress response are not fully understood. Here, a stress-responsive MADS-box TF OsMADS23 from rice conferring the osmotic stress tolerance in plants is reported. Overexpression of OsMADS23 remarkably enhanced, but knockout of the gene greatly reduced the drought and salt tolerance in rice plants. Further, OsMADS23 was shown to promote the biosynthesis of endogenous ABA and proline by activating the transcription of target genes OsNCED2, OsNCED3, OsNCED4 and OsP5CR that are key components for ABA and proline biosynthesis, respectively. Then, the convincing evidence showed that the OsNCED2-knockout mutants had lower ABA levels and exhibited higher sensitivity to drought and oxidative stress than wild type, which is similar to osmads23 mutant. Interestingly, the SnRK2-type protein kinase SAPK9 was found to physically interact with and phosphorylate OsMADS23, and thus increase its stability and transcriptional activity. Furthermore, the activation of OsMADS23 by SAPK9-mediated phosphorylation is dependent on ABA in plants. Collectively, these findings establish a mechanism that OsMADS23 functions as a positive regulator in response to osmotic stress by regulating ABA biosynthesis, and provide a new strategy for improving drought and salt tolerance in rice.