Gibberellin metabolism and its regulation

Gene editing of ZmGA20ox3 improves plant architecture and drought tolerance in maize

KEY MESSAGE

Editing ZmGA20ox3 can achieve the effect similar to applying Cycocel, which can reduce maize plant height and enhance stress resistance. Drought stress, a major plant abiotic stress, is capable of suppressing crop yield performance severely. However, the trade-off between crop drought tolerance and yield performance turns out to be significantly challenging in drought-resistant crop breeding. Several phytohormones [e.g., gibberellin (GA)] have been reported to play a certain role in plant drought response, which also take on critical significance in plant growth and development. In this study, the loss-of-function mutations of GA biosynthesis enzyme ZmGA20ox3 were produced using the CRISPR-Cas9 system in maize. As indicated by the result of 2-year field trials, the above-mentioned mutants displayed semi-dwarfing phenotype with the decrease of GA1, and almost no yield loss was generated compared with wild-type (WT) plants. Interestingly, as revealed by the transcriptome analysis, differential expressed genes (DEGs) were notably enriched in abiotic stress progresses, and biochemical tests indicated the significantly increased ABA, JA, and DIMBOA levels in mutants, suggesting that ZmGA20ox3 may take on vital significance in stress response in maize. The in-depth analysis suggested that the loss function of ZmGA20ox3 can enhance drought tolerance in maize seedling, reduce Anthesis-Silking Interval (ASI) delay while decreasing the yield loss significantly in the field under drought conditions. The results of this study supported that regulating ZmGA20ox3 can improve plant height while enhancing drought resistance in maize, thus serving as a novel method for drought-resistant genetic improvement in maize.

Characterization of diterpene synthase genes in Brachypodium distachyon, a monocotyledonous model plant, provides evolutionary insight into their multiple homologs in cereals

Gibberellins are diterpenoid phytohormones that regulate plant growth, and are biosynthesized from a diterpene intermediate, ent-kaurene, which is produced from geranylgeranyl diphosphate via ent-copalyl diphosphate (ent-CDP). The successive 2 cyclization reactions are catalyzed by 2 distinct diterpene synthases, ent-CDP synthase (ent-CPS) and ent-kaurene synthase (KS). Various diterpene synthase genes involved in specialized metabolism were likely created through duplication and neofunctionalization of gibberellin-biosynthetic ent-CPS and KS genes in crops. Brachypodium distachyon is a monocotyledonous species that is a model plant in grasses. We herein found 1 ent-CPS gene homolog BdCPS and 4 tandemly arrayed KS-like genes BdKS1, KSL2, KSL3, and KSL4 in the B. distachyon genome, a simpler collection of paralogs than in crops. Phylogenetic and biochemical analyses showed that BdCPS and BdKS1 are responsible for gibberellin biosynthesis. BdKSL2 and BdKSL3 are suggested to be involved in specialized diterpenoid metabolism. Moreover, we restored KS activity of BdKSL2 through amino acid substitution.

Global analysis of seed transcriptomes reveals a novel PLATZ regulator for seed size and weight control in soybean

Seed size and weight are important factors that influence soybean yield. Combining the weighted gene co-expression network analysis (WGCNA) of 45 soybean accessions and gene dynamic changes in seeds at seven developmental stages, we identified candidate genes that may control the seed size/weight. Among these, a PLATZ-type regulator overlapping with 10 seed weight QTLs was further investigated. This zinc-finger transcriptional regulator, named as GmPLATZ, is required for the promotion of seed size and weight in soybean. The GmPLATZ may exert its functions through direct binding to the promoters and activation of the expression of cyclin genes and GmGA20OX for cell proliferation. Overexpression of the GmGA20OX enhanced seed size/weight in soybean. We further found that the GmPLATZ binds to a 32-bp sequence containing a core palindromic element AATGCGCATT. Spacing of the flanking sequences beyond the core element facilitated GmPLATZ binding. An elite haplotype Hap3 was also identified to have higher promoter activity and correlated with higher gene expression and higher seed weight. Orthologues of the GmPLATZ from rice and Arabidopsis play similar roles in seeds. Our study reveals a novel module of GmPLATZ-GmGA20OX/cyclins in regulating seed size and weight and provides valuable targets for breeding of crops with desirable agronomic traits.

Gibberellic Acid Inhibits Dendrobium nobile-Piriformospora Symbiosis by Regulating the Expression of Cell Wall Metabolism Genes

Orchid seeds lack endosperms and depend on mycorrhizal fungi for germination and nutrition acquisition under natural conditions. Piriformospora indica is a mycorrhizal fungus that promotes seed germination and seedling development in epiphytic orchids, such as Dendrobium nobile. To understand the impact of P. indica on D. nobile seed germination, we examined endogenous hormone levels by using liquid chromatography-mass spectrometry. We performed transcriptomic analysis of D. nobile protocorm at two developmental stages under asymbiotic germination (AG) and symbiotic germination (SG) conditions. The result showed that the level of endogenous IAA in the SG protocorm treatments was significantly higher than that in the AG protocorm treatments. Meanwhile, GA3 was only detected in the SG protocorm stages. IAA and GA synthesis and signaling genes were upregulated in the SG protocorm stages. Exogenous GA3 application inhibited fungal colonization inside the protocorm, and a GA biosynthesis inhibitor (PAC) promoted fungal colonization. Furthermore, we found that PAC prevented fungal hyphae collapse and degeneration in the protocorm, and differentially expressed genes related to cell wall metabolism were identified between the SG and AG protocorm stages. Exogenous GA3 upregulated SRC2 and LRX4 expression, leading to decreased fungal colonization. Meanwhile, GA inhibitors upregulated EXP6, EXB16, and EXP10-2 expression, leading to increased fungal colonization. Our findings suggest that GA regulates the expression of cell wall metabolism genes in D. nobile, thereby inhibiting the establishment of mycorrhizal symbiosis.

Genome resequencing reveals the evolutionary history of garlic reproduction traits

The propagation of cultivated garlic relies on vegetative cloves, thus flowers become non-essential for reproduction in this species, driving the evolution of reproductive feature-derived traits. To obtain insights into the evolutionary alteration of reproductive traits in the clonally propagated garlic, the evolutionary histories of two main reproduction-related traits, bolting and flower differentiation, were explored by genome analyses using 134 accessions displaying wide diversity in these two traits. Resequencing identified 272.8 million variations in the garlic genome, 198.0 million of which represent novel variants. Population analysis identified five garlic groups that have evolved into two clades. Gene expression, single-cell transcriptome sequencing, and genome-wide trait association analyses have identified numerous candidates that correlate with reproductive transition and flower development, some of which display distinct selection signatures. Selective forces acting on the B-box zinc finger protein-encoding Asa2G00291.1, the global transcription factor group E protein-encoding Asa5G01527.1, and VERNALIZATION INSENSITIVE 3-like Asa3G03399.1 appear to be representative of the evolution of garlic bolting. Plenty of novel genomic variations and trait-related candidates represent valuable resources for biological studies of garlic. Numerous selective signatures from genes associated with the two chosen reproductive traits provide important insights into the evolutionary history of reproduction in this clonally propagated crop.

Coordination of growth and drought responses by GA-ABA signaling in rice

The drought caused by global warming seriously affects the crop growth and agricultural production. Plants have evolved distinct strategies to cope with the drought environment. Under drought stress, energy and resources should be diverted from growth toward stress management. However, the molecular mechanism underlying coordination of growth and drought response remains largely elusive. Here, we discovered that most of the gibberellin (GA) metabolic genes were regulated by water scarcity in rice, leading to the lower GA contents and hence inhibited plant growth. Low GA contents resulted in the accumulation of more GA signaling negative regulator SLENDER RICE 1, which inhibited the degradation of abscisic acid (ABA) receptor PYL10 by competitively binding to the co-activator of anaphase-promoting complex TAD1, resulting in the enhanced ABA response and drought tolerance. These results elucidate the synergistic regulation of crop growth inhibition and promotion of drought tolerance and survival, and provide useful genetic resource in breeding improvement of crop drought resistance.

Important Factors Controlling Gibberellin Homeostasis in Plant Height Regulation

Plant height is an important agronomic trait that is closely associated with crop yield and quality. Gibberellins (GAs), a class of highly efficient plant growth regulators, play key roles in regulating plant height. Increasing reports indicate that transcriptional regulation is a major point of regulation of the GA pathways. Although substantial knowledge has been gained regarding GA biosynthetic and signaling pathways, important factors contributing to the regulatory mechanisms homeostatically controlling GA levels remain to be elucidated. Here, we provide an overview of current knowledge regarding the regulatory network involving transcription factors, noncoding RNAs, and histone modifications involved in GA pathways. We also discuss the mechanisms of interaction between GAs and other hormones in plant height development. Finally, future directions for applying knowledge of the GA hormone in crop breeding are described.

Jasmonate inhibits plant growth and reduces gibberellin levels via microRNA5998 and transcription factor MYC2

Jasmonate (JA) and gibberellins (GAs) exert antagonistic effects on plant growth and development in response to environmental and endogenous stimuli. Although the crosstalk between JA and GA has been elucidated, the role of JA in GA biosynthesis remains unclear. Therefore, in this study, we investigated the mechanism underlying JA-mediated regulation of endogenous GA levels in Arabidopsis (Arabidopsis thaliana). Transient and electrophoretic mobility shift assays showed that transcription factor MYC2 regulates GA inactivation genes. Using transgenic plants, we further evaluated the contribution of MYC2 in regulating GA inactivation genes. JA treatment increased DELLA accumulation but did not inhibit DELLA protein degradation. Additionally, JA treatment decreased bioactive GA content, including GA4, significantly decreased the expression of GA biosynthesis genes, including ent-kaurene synthase (AtKS), GA 3β-hydroxylase (AtGA3ox1), and AtGA3ox2, and increased the expression of GA inactivation genes, including GA 2 oxidase (AtGA2ox4), AtGA2ox7, and AtGA2ox9. Conversely, JA treatment did not significantly affect gene expression in the myc2 myc3 myc4 triple mutant, demonstrating the MYC2-4-dependent effects of JA in GA biosynthesis. Additionally, JA post-transcriptionally regulated AtGA3ox1 expression. We identified microRNA miR5998 as an AtGA3ox1-associated miRNA; its overexpression inhibited plant growth by suppressing AtGA3ox1 expression. Overall, our findings indicate that JA treatment inhibits endogenous GA levels and plant growth by decreasing the expression of GA biosynthesis genes and increasing the expression of GA inactivation genes via miR5998 and MYC2 activities.

Phytohormonal modulation of the drought stress in soybean: outlook, research progress, and cross-talk

Phytohormones play vital roles in stress modulation and enhancing the growth of plants. They interact with one another to produce programmed signaling responses by regulating gene expression. Environmental stress, including drought stress, hampers food and energy security. Drought is abiotic stress that negatively affects the productivity of the crops. Abscisic acid (ABA) acts as a prime controller during an acute transient response that leads to stomatal closure. Under long-term stress conditions, ABA interacts with other hormones, such as jasmonic acid (JA), gibberellins (GAs), salicylic acid (SA), and brassinosteroids (BRs), to promote stomatal closure by regulating genetic expression. Regarding antagonistic approaches, cytokinins (CK) and auxins (IAA) regulate stomatal opening. Exogenous application of phytohormone enhances drought stress tolerance in soybean. Thus, phytohormone-producing microbes have received considerable attention from researchers owing to their ability to enhance drought-stress tolerance and regulate biological processes in plants. The present study was conducted to summarize the role of phytohormones (exogenous and endogenous) and their corresponding microbes in drought stress tolerance in model plant soybean. A total of n=137 relevant studies were collected and reviewed using different research databases.

Effect of Mowing on Wheat Growth at Seeding Stage

Winter wheat is used as forage at the tillering stage in many countries; however, the regrowth pattern of wheat after mowing remains unclear. In this study, the growth patterns of wheat were revealed through cytological and physiological assessments as well as transcriptome sequencing. The results of agronomic traits and paraffin sections showed that the shoot growth rate increased, but root growth was inhibited after mowing. The submicroscopic structure revealed a decrease in heterochromatin in the tillering node cell and a change in mitochondrial shape in the tillering node and secondary root. Analysis of the transcriptome showed the number of differentially expressed genes (DEGs) involved in biological processes, cellular components, and molecular functions; 2492 upregulated DEGs and 1534 downregulated DEGs were identified. The results of the experimental study showed that mowing induced expression of DEGs in the phenylpropanoid biosynthesis pathway and increased the activity of PAL and 4CL. The upregulated DEGs in the starch and sucrose metabolism pathways and related enzyme activity alterations indicated that the sugar degradation rate increased. The DEGs in the nitrogen metabolism pathway biosynthesis of the amino acids, phenylpropanoid biosynthesis metabolism, and in the TCA pathway also changed after mowing. Hormone content and related gene expression was also altered in the tillering and secondary roots after mowing. When jasmonic acid and ethylene were used to treat the wheat after mowing, the regeneration rate increased, whereas abscisic acid inhibited regrowth. This study revealed the wheat growth patterns after mowing, which could lead to a better understanding of the development of dual-purpose wheat.

Research on the Effect of Oriental Fruit Moth Feeding on the Quality Degradation of Chestnut Rose Juice Based on Metabolomics

As a native fruit of China, chestnut rose (Rosa roxburghii Tratt) juice is rich in bioactive ingredients. Oriental fruit moth (OFM), Grapholita molesta (Busck), attacks the fruits and shoots of Rosaceae plants, and its feeding affects the quality and yield of chestnut rose. To investigate the effects of OFM feeding on the quality of chestnut rose juice, the bioactive compounds in chestnut rose juice produced from fruits eaten by OFM were measured. The electronic tongue senses, amino acid profile, and untargeted metabolomics assessments were performed to explore changes in the flavour and metabolites. The results showed that OFM feeding reduced the levels of superoxide dismutase (SOD), tannin, vitamin C, flavonoid, and condensed tannin; increased those of polyphenols, soluble solids, total protein, bitterness, and amounts of bitter amino acids; and decreased the total amino acid and umami amino acid levels. Furthermore, untargeted metabolomics annotated a total of 426 differential metabolites (including 55 bitter metabolites), which were mainly enriched in 14 metabolic pathways, such as flavonoid biosynthesis, tryptophan metabolism, tyrosine metabolism, and diterpenoid biosynthesis. In conclusion, the quality of chestnut rose juice deteriorated under OFM feeding stress, the levels of bitter substances were significantly increased, and the bitter taste was subsequently enhanced.

A gibberellin-deficient maize mutant exhibits altered plant height, stem strength and drought tolerance

KEY MESSAGE

The reduction in endogenous gibberellin improved drought resistance, but decreased cellulose and lignin contents, which made the mutant prone to lodging. It is well known that gibberellin (GA) is a hormone that plays a vital role in plant growth and development. In recent years, a growing number of studies have found that gibberellin plays an important role in regulating the plant height, stem length, and stressed growth surfaces. In this study, a dwarf maize mutant was screened from an EMS-induced mutant library of maize B73. The mutated gene was identified as KS, which encodes an ent-kaurene synthase (KS) enzyme functioning in the early biosynthesis of GA. The mutant was named as ks3-1. A significant decrease in endogenous GA levels was verified in ks3-1. A significantly decreased stem strength of ks3-1, compared with that of wild-type B73, was found. Significant decreases in the cellulose and lignin contents, as well as the number of epidermal cell layers, were further characterized in ks3-1. The expression levels of genes responsible for cellulose and lignin biosynthesis were induced by exogenous GA treatment. Under drought stress conditions, the survival rate of ks3-1 was significantly higher than that of the wild-type B73. The survival rates of both wild-type B73 and ks3-1 decreased significantly after exogenous GA treatment. In conclusion, we summarized that a decreased level of GA in ks3-1 caused a decreased plant height, a decreased stem strength as a result of cell wall defects, and an increased drought tolerance. Our results shed light on the importance of GA and GA-defective mutants in the genetic improvement of maize and breeding maize varieties.

Down-regulation of SlGT-26 gene confers dwarf plants and enhances drought and salt stress resistance in tomato

Plant architecture, an important agronomic trait closely associated with yield, is governed by a highly intricate molecular network. Despite extensive research, many mysteries surrounding this regulation remain unresolved. Trihelix transcription factor family plays a crucial role in the development of plant morphology and abiotic stresses. Here, we identified a novel trihelix transcription factor named SlGT-26, and its down-regulation led to significant alterations in plant architecture, including dwarfing, reduced internode length, smaller leaves, and shorter petioles. The dwarf phenotype of SlGT-26 silenced transgenic plants could be recovered after spraying exogenous GA3, and the GA3 content were decreased in the RNAi plants. Additionally, the expression levels of gibberellin-related genes were affected in the RNAi lines. These results indicate that the dwarf of SlGT-26-RNAi plants may be a kind of GA3-sensitive dwarf. SlGT-26 was response to drought and salt stress treatments. SlGT-26-RNAi transgenic plants demonstrated significantly enhanced drought resistance and salt tolerance in comparison to their wild-type tomato counterparts. SlGT-26-RNAi transgenic plants grew better, had higher relative water content and lower MDA and H2O2 contents. The expression of multiple stress-related genes was also up-regulated. In summary, we have discovered a novel gene, SlGT-26, which plays a crucial role in regulating plant architecture and in respond to drought and salt stress.

The cytochrome P450 gene, MdCYP716B1, is involved in regulating plant growth and anthracnose resistance in apple

Apple is one of the main cultivated fruit trees worldwide. Both biotic and abiotic stresses, especially fungal diseases, have serious effects on the growth and fruit quality of apples. Cytochrome P450, the largest protein family in plants, is critical for plant growth and stress responses. However, the function of apple P450 remains poorly understood. In our previous study, 'Hanfu' autotetraploid showed dwarfism and fungal resistance phenotypes compared to 'Hanfu' diploid. Digital gene expression sequencing analysis revealed that the transcript level of MdCYP716B1 was significantly downregulated in the autotetraploid apple cultivar 'Hanfu'. In this study, we identified and cloned the MdCYP716B1 gene from 'Hanfu' apples. The MdCYP716B1 protein fused to a green fluorescent protein was localized in the cytoplasm. We constructed the plant overexpression vector and RNAi vector of MdCYP716B1, and the apple 'GL-3' was transformed by Agrobacterium-mediated transformation to obtain transgenic plants. Overexpressing and RNAi silencing transgenic plants exhibited an increase and decrease in plant height to 'GL-3', respectively. RNAi silencing transgenic plants displayed increased resistance to Colletotrichum gloeosporioides, whereas overexpression transgenic plants were more sensitive to C. gloeosporioides. According to transcriptome analysis, the transcript levels of gibberellin biosynthesis genes were upregulated in MdCYP716B1-overexpression plants. In contrast with 'GL-3', GA3 accumulation was rose in MdCYP716B1-OE lines and impaired in MdCYP716B1-RNAi lines. Collectively, our data indicate that MdCYP716B1 regulates plant growth and resistance to fungal stress.

AtHSPR functions in gibberellin-mediated primary root growth by interacting with KNAT5 and OFP1 in Arabidopsis

KEY MESSAGE

AtHSPR forms a complex with KNAT5 and OFP1 to regulate primary root growth through GA-mediated root meristem activity. KNAT5-OFP1 functions as a negative regulator of AtHSPR in response to GA. Plant root growth is modulated by gibberellic acid (GA) signaling and depends on root meristem maintenance. ARABIDOPSIS THALIANA HEAT SHOCK PROTEIN-RELATED (AtHSPR) is a vital regulator of flowering time and salt stress tolerance. However, little is known about the role of AtHSPR in the regulation of primary root growth. Here, we report that athspr mutant exhibits a shorter primary root compared to wild type and that AtHSPR interacts with KNOTTED1-LIKE HOMEOBOX GENE 5 (KNAT5) and OVATE FAMILY PROTEIN 1 (OFP1). Genetic analysis showed that overexpression of KNAT5 or OFP1 caused a defect in primary root growth similar to that of the athspr mutant, but knockout of KNAT5 or OFP1 rescued the short root phenotype in the athspr mutant by altering root meristem activity. Further investigation revealed that KNAT5 interacts with OFP1 and that AtHSPR weakens the inhibition of GIBBERELLIN 20-OXIDASE 1 (GA20ox1) expression by the KNAT5-OFP1 complex. Moreover, root meristem cell proliferation and root elongation in 35S::KNAT5athspr and 35S::OFP1athspr seedlings were hypersensitive to GA3 treatment compared to the athspr mutant. Together, our results demonstrate that the AtHSPR-KNAT5-OFP1 module regulates root growth and development by impacting the expression of GA biosynthetic gene GA20ox1, which could be a way for plants to achieve plasticity in response to the environment.

Jasmonate-mediated gibberellin catabolism constrains growth during herbivore attack in rice

Plant defense against herbivores is costly and often associated with growth repression. The phytohormone jasmonate (JA) plays a central role in prioritizing defense over growth during herbivore attack, but the underlying mechanisms remain unclear. When brown planthoppers (BPH, Nilaparvata lugens) attack rice (Oryza sativa), growth is dramatically suppressed. BPH infestation also increases inactive gibberellin (GA) levels and transcripts of GA 2-oxidase (GA2ox) genes, 2 (GA2ox3 and GA2ox7) of which encode enzymes that catalyze the conversion of bioactive GAs to inactive GAs in vitro and in vivo. Mutation of these GA2oxs diminishes BPH-elicited growth restriction without affecting BPH resistance. Phytohormone profiling and transcriptome analyses revealed that GA2ox-mediated GA catabolism was enhanced by JA signaling. The transcript levels of GA2ox3 and GA2ox7 were significantly attenuated under BPH attack in JA biosynthesis (allene oxide cyclase [aoc]) or signaling-deficient (myc2) mutants. In contrast, GA2ox3 and GA2ox7 expression was increased in MYC2 overexpression lines. MYC2 directly binds to the G-boxes in the promoters of both GA2ox genes to regulate their expression. We conclude that JA signaling simultaneously activates defense responses and GA catabolism to rapidly optimize resource allocation in attacked plants and provides a mechanism for phytohormone crosstalk.

Targeted metabolome and transcriptome analyses reveal changes in gibberellin and related cell wall-acting enzyme-encoding genes during stipe elongation in Flammulina filiformis

Flammulina filiformis, a typical agaric fungus, is a widely cultivated and consumed edible mushroom. Elongation of its stipe (as the main edible part) is closely related to its yield and commercial traits; however, the endogenous hormones during stipe elongation and their regulatory mechanisms are not well understood. Gibberellin (GA) plays an important role in the regulation of plant growth, but little has been reported in macro fungi. In this study, we first treated F. filiformis stipes in the young stage with PBZ (an inhibitor of GA) and found that PBZ significantly inhibited elongation of the stipe. Then, we performed GA-targeted metabolome and transcriptome analyses of the stipe at both the young and elongation stages. A total of 13 types of GAs were detected in F. filiformis; the contents of ten of them, namely, GA3, GA4, GA8, GA14, GA19, GA20, GA24, GA34, GA44, and GA53, were significantly decreased, and the contents of three (GA5, GA9, and GA29) were significantly increased during stipe elongation. Transcriptome analysis showed that the genes in the terpenoid backbone biosynthesis pathway showed varying expression patterns: HMGS, HMGR, GPS, and FPPS were significantly upregulated, while CPS/KS had no significant difference in transcript level during stipe elongation. In total, 37 P450 genes were annotated to be involved in GA biosynthesis; eight of them were upregulated, twelve were downregulated, and the rest were not differentially expressed. In addition, four types of differentially expressed genes involved in stipe elongation were identified, including six signal transduction genes, five cell cycle-controlling genes, twelve cell wall-related enzymes and six transcription factors. The results identified the types and content of GAs and the expression patterns of their synthesis pathways during elongation in F. filiformis and revealed the molecular mechanisms by which GAs may affect the synthesis of cell wall components and the cell cycle of the stipe through the downstream action of cell wall-related enzymes, transcription factors, signal transduction and cell cycle control, thus regulating stipe elongation. This study is helpful for understanding the roles of GAs in stipe development in mushrooms and lays the foundation for the rational regulation of stipe length in agaric mushrooms during production.

Hyphal Growth and Conidia Germination Are Induced by Phytohormones in the Root Colonizing and Plant Growth Promoting Fungus Metarhizium guizhouense

Beneficial associations are very important for plants and soil-dwelling microorganisms in different ecological niches, where communication by chemical signals is relevant. Among the chemical signals, the release of phytohormones by plants is important to establish beneficial associations with fungi, and a recently described association is that of the entomopathogenic ascomycete fungus Metarhizium with plants. Here, we evaluated the effect of four different phytohormones, synthetic strigolactone (GR24), sorgolactone (SorL), 3-indolacetic acid (IAA) and gibberellic acid (GA3), on the fungus Metarhizium guizhouense strain HA11-2, where the germination rate and hyphal elongation were determined at three different times. All phytohormones had a positive effect on germination, with GA3 showing the greatest effect, and for hyphal length, on average, the group treated with synthetic strigolactone GR24 showed greater average hyphal length at 10 h of induction. This work expands the knowledge of the effect of phytohormones on the fungus M. guizhouense, as possible chemical signals for the rapid establishment of the fungus-plant association.

Gibberellins Promote Seed Conditioning by Up-Regulating Strigolactone Receptors in the Parasitic Plant Striga hermonthica

Dormant seeds of the root parasitic plant Striga hermonthica sense strigolactones from host plants as environmental cues for germination. This process is mediated by a diversified member of the strigolactone receptors encoded by HYPOSENSITIVE TO LIGHT/KARRIKIN INSENSITIVE2 genes. It is known that warm and moist treatment during seed conditioning gradually makes dormant Striga seeds competent to respond to strigolactones, although the mechanism behind it is poorly understood. In this report, we show that plant hormone gibberellins increase strigolactone competence by up-regulating mRNA expression of the major strigolactone receptors during the conditioning period. This idea was supported by a poor germination phenotype in which gibberellin biosynthesis was depleted by paclobutrazol during conditioning. Moreover, live imaging with a fluorogenic strigolactone mimic, yoshimulactone green W, revealed that paclobutrazol treatment during conditioning caused aberrant dynamics of strigolactone perception after germination. These observations revealed an indirect role of gibberellins in seed germination in Striga, which contrasts with their roles as dominant germination-stimulating hormones in non-parasitic plants. We propose a model of how the role of gibberellins became indirect during the evolution of parasitism in plants. Our work also highlights the potential role for gibberellins in field applications, for instance, in elevating the sensitivity of seeds toward strigolactones in the current suicidal germination approach to alleviate the agricultural threats caused by this parasite in Africa.

Strigolactones and Shoot Branching: What Is the Real Hormone and How Does It Work?

There have been substantial advances in our understanding of many aspects of strigolactone regulation of branching since the discovery of strigolactones as phytohormones. These include further insights into the network of phytohormones and other signals that regulate branching, as well as deep insights into strigolactone biosynthesis, metabolism, transport, perception and downstream signaling. In this review, we provide an update on recent advances in our understanding of how the strigolactone pathway co-ordinately and dynamically regulates bud outgrowth and pose some important outstanding questions that are yet to be resolved.

Temporal and spatial transcriptional regulation of phytohormone metabolism during seed development in barley (Hordeum vulgare L.)

Plant hormones play important roles in seed development; however, transcriptional regulation of their metabolism and levels of the respective bioactive forms during barley seed development is poorly understood. To this end, this study performed a comprehensive analysis of changes in the expression patterns phytohormone metabolism genes and levels of the respective bioactive forms in the embryo and endosperm tissues. Our study showed the presence of elevated levels of abscisic acid (ABA), bioactive forms of gibberellins (GAs), jasmonate (JA) and cytokinins (CKs), auxin and salicylic acid (SA) in the endosperm and embryo tissues at early stage of seed filling (SF). The levels of all hormones in both tissues, except that of ABA, decreased to low levels during SF. In contrast, embryonic ABA level increased during SF and peaked at physiological maturity (PM) while the endospermic ABA was maintained at a similar level observed during SF. Although its level decreased high amount of ABA was still present in the embryo during post-PM. We detected low levels of ABA in the endosperm and all the other hormones in both tissues during post-PM phase except the relatively higher levels of jasmonoyl-isoleucine and SA detected at late stage of post-PM. Our data also showed that spatiotemporal changes in the levels of plant hormones during barley seed development are mediated by the expression of specific genes involved in their respective metabolic pathways. These results indicate that seed development in barley is mediated by spatiotemporal modulation in the metabolism and levels of plant hormones.

Promoter deletion in the soybean Compact mutant leads to overexpression of a gene with homology to the C20-gibberellin 2-oxidase family

Height is a critical component of plant architecture, significantly affecting crop yield. The genetic basis of this trait in soybean remains unclear. In this study, we report the characterization of the Compact mutant of soybean, which has short internodes. The candidate gene was mapped to chromosome 17, and the interval containing the causative mutation was further delineated using biparental mapping. Whole-genome sequencing of the mutant revealed an 8.7 kb deletion in the promoter of the Glyma.17g145200 gene, which encodes a member of the class III gibberellin (GA) 2-oxidases. The mutation has a dominant effect, likely via increased expression of the GA 2-oxidase transcript observed in green tissue, as a result of the deletion in the promoter of Glyma.17g145200. We further demonstrate that levels of GA precursors are altered in the Compact mutant, supporting a role in GA metabolism, and that the mutant phenotype can be rescued with exogenous GA3. We also determined that overexpression of Glyma.17g145200 in Arabidopsis results in dwarfed plants. Thus, gain of promoter activity in the Compact mutant leads to a short internode phenotype in soybean through altered metabolism of gibberellin precursors. These results provide an example of how structural variation can control an important crop trait and a role for Glyma.17g145200 in soybean architecture, with potential implications for increasing crop yield.

The DELLA-ABI4-HY5 module integrates light and gibberellin signals to regulate hypocotyl elongation

Plant growth is coordinately controlled by various environmental and hormonal signals, of which light and gibberellin (GA) signals are two critical factors with opposite effects on hypocotyl elongation. Although interactions between the light and GA signaling pathways have been studied extensively, the detailed regulatory mechanism of their direct crosstalk in hypocotyl elongation remains to be fully clarified. Previously, we reported that ABA INSENSITIVE 4 (ABI4) controls hypocotyl elongation through its regulation of cell-elongation-related genes, but whether it is also involved in GA signaling to promote hypocotyl elongation is unknown. In this study, we show that promotion of hypocotyl elongation by GA is dependent on ABI4 activation. DELLAs interact directly with ABI4 and inhibit its DNA-binding activity. In turn, ABI4 combined with ELONGATED HYPOCOTYL 5 (HY5), a key positive factor in light signaling, feedback regulates the expression of the GA2ox GA catabolism genes and thus modulates GA levels. Taken together, our results suggest that the DELLA-ABI4-HY5 module may serve as a molecular link that integrates GA and light signals to control hypocotyl elongation.

Histology, physiology, and transcriptomic and metabolomic profiling reveal the developmental dynamics of annual shoots in tree peonies (Paeonia suffruticosa Andr.)

The development of tree peony annual shoots is characterized by "withering", which is related to whether there are bud points in the leaf axillaries of annual shoots. However, the mechanism of "withering" in tree peony is still unclear. In this study, Paeonia ostii 'Fengdan' and P. suffruticosa 'Luoyanghong' were used to investigate dynamic changes of annual shoots through anatomy, physiology, transcriptome, and metabolome. The results demonstrated that the developmental dynamics of annual shoots of the two cultivars were comparable. The withering degree of P. suffruticosa 'Luoyanghong' was higher than that of P. ostii 'Fengdan', and their upper internodes of annual flowering shoots had a lower degree of lignin deposition, cellulose, C/N ratio, showing no obvious sclerenchyma, than the bottom ones and the whole internodes of vegetative shoot, which resulted in the "withering" of upper internodes. A total of 36 phytohormone metabolites were detected, of which 33 and 31 were detected in P. ostii 'Fengdan' and P. suffruticosa 'Luoyanghong', respectively. In addition, 302 and 240 differentially expressed genes related to lignin biosynthesis, carbon and nitrogen metabolism, plant hormone signal transduction, and zeatin biosynthesis were screened from the two cultivars. Furtherly, 36 structural genes and 40 transcription factors associated with the development of annual shoots were highly co-expressed, and eight hub genes involved in this developmental process were identified. Consequently, this study explained the developmental dynamic on the varied annual shoots through multi-omics, providing a theoretical foundation for germplasm innovation and the mechanized harvesting of tree peony annual shoots.

Identification of novel candidate loci and genes for seed vigor-related traits in upland cotton (Gossypium hirsutum L.) via GWAS

Seed vigor (SV) is a crucial trait determining the quality of crop seeds. Currently, over 80% of China's cotton-planting area is in Xinjiang Province, where a fully mechanized planting model is adopted, accounting for more than 90% of the total fiber production. Therefore, identifying SV-related loci and genes is crucial for improving cotton yield in Xinjiang. In this study, three seed vigor-related traits, including germination potential, germination rate, and germination index, were investigated across three environments in a panel of 355 diverse accessions based on 2,261,854 high-quality single-nucleotide polymorphisms (SNPs). A total of 26 significant SNPs were detected and divided into six quantitative trait locus regions, including 121 predicted candidate genes. By combining gene expression, gene annotation, and haplotype analysis, two novel candidate genes (Ghir_A09G002730 and Ghir_D03G009280) within qGR-A09-1 and qGI/GP/GR-D03-3 were associated with vigor-related traits, and Ghir_A09G002730 was found to be involved in artificial selection during cotton breeding by population genetic analysis. Thus, understanding the genetic mechanisms underlying seed vigor-related traits in cotton could help increase the efficiency of direct seeding by molecular marker-assisted selection breeding.

Wheat gibberellin oxidase genes and their functions in regulating tillering

Multiple genetic factors control tillering, a key agronomy trait for wheat (Triticum aestivum L.) yield. Previously, we reported a dwarf-monoculm mutant (dmc) derived from wheat cultivar Guomai 301, and found that the contents of gibberellic acid 3 (GA3) in the tiller primordia of dmc were significantly higher. Transcriptome analysis indicated that some wheat gibberellin oxidase (TaGAox) genes TaGA20ox-A2, TaGA20ox-B2, TaGA3ox-A2, TaGA20ox-A4, TaGA2ox-A10 and TaGA2ox-B10 were differentially expressed in dmc. Therefore, this study systematically analyzed the roles of gibberellin oxidase genes during wheat tillering. A total of 63 TaGAox genes were identified by whole genome analysis. The TaGAoxs were clustered to four subfamilies, GA20oxs, GA2oxs, GA3oxs and GA7oxs, including seven subgroups based on their protein structures. The promoter regions of TaGAox genes contain a large number of cis-acting elements closely related to hormone, plant growth and development, light, and abiotic stress responses. Segmental duplication events played a major role in TaGAoxs expansion. Compared to Arabidopsis, the gene collinearity degrees of the GAoxs were significantly higher among wheat, rice and maize. TaGAox genes showed tissue-specific expression patterns. The expressions of TaGAox genes (TaGA20ox-B2, TaGA7ox-A1, TaGA2ox10 and TaGA3ox-A2) were significantly affected by exogenous GA3 applications, which also significantly promoted tillering of Guomai 301, but didn't promote dmc. TaGA7ox-A1 overexpression transgenic wheat lines were obtained by Agrobacterium mediated transformation. Genomic PCR and first-generation sequencing demonstrated that the gene was integrated into the wheat genome. Association analysis of TaGA7ox-A1 expression level and tiller number per plant demonstrated that the tillering capacities of some TaGA7ox-A1 transgenic lines were increased. These data demonstrated that some TaGAoxs as well as GA signaling were involved in regulating wheat tillering, but the GA signaling pathway was disturbed in dmc. This study provided valuable clues for functional characterization of GAox genes in wheat.

Ectopic expression of Camellia oleifera Abel. gibberellin 20-oxidase gene increased plant height and promoted secondary cell walls deposition in Arabidopsis

MAIN CONCLUSION

Ectopic expression of Camellia oleifera Abel. gibberellin 20-oxidase 1 caused a taller phenotype, promoted secondary cell wall deposition, leaf enlargement, and early flowering, and reduced chlorophyll and anthocyanin accumulation and seed enlargement phenotype in Arabidopsis. Plant height and secondary cell wall (SCW) deposition are important plant traits. Gibberellins (GAs) play important roles in regulating plant height and SCWs deposition. Gibberellin 20-oxidase (GA20ox) is an important enzyme involved in GA biosynthesis. In the present study, we identified a GA synthesis gene in Camellia oleifera. The total length of the CoGA20ox1 gene sequence was 1146 bp, encoding 381 amino acids. Transgenic plants with CoGA20ox1 had a taller phenotype; a seed enlargement phenotype; promoted SCWs deposition, leaf enlargement, and early flowering; and reduced chlorophyll and anthocyanin accumulation. Genetic analysis showed that the mutant ga20ox1-3 Arabidopsis partially rescued the phenotype of CoGA20ox1 overexpression plants. The results showed that CoGA20ox1 participates in the growth and development of C. oleifera. The morphological changes in CoGA20ox1 overexpressed plants provide a theoretical basis for further exploration of GA biosynthesis and analysis of the molecular mechanism in C. oleifera.

GA20ox Family Genes Mediate Gibberellin and Auxin Crosstalk in Moso bamboo (Phyllostachys edulis)

Moso bamboo (Phyllostachys edulis) is one of the fastest growing plants. Gibberellin (GA) is a key phytohormone regulating growth, but there are few studies on the growth of Moso bamboo regulated by GA. The gibberellin 20 oxidase (GA20ox) gene family was targeted in this study. Chromosomal distribution and collinearity analysis identified 10 GA20ox genes evenly distributed on chromosomes, and the family genes were relatively conservative in evolution. The genetic relationship of GA20ox genes had been confirmed to be closest in different genera of plants in a phylogenetic and selective pressure analysis between Moso bamboo and rice. About 1/3 GA20ox genes experienced positive selective pressure with segmental duplication being the main driver of gene family expansion. Analysis of expression patterns revealed that only six PheGA20ox genes were expressed in different organs of shoot development and flowers, that there was redundancy in gene function. Underground organs were not the main site of GA synthesis in Moso bamboo, and floral organs are involved in the GA biosynthesis process. The auxin signaling factor PheARF47 was located upstream of PheGA20ox3 and PheGA20ox6 genes, where PheARF47 regulated PheGA20ox3 through cis-P box elements and cis-AuxRR elements, based on the result that promoter analysis combined with yeast one-hybrid and dual luciferase detection analysis identified. Overall, we identified the evolutionary pattern of PheGA20ox genes in Moso bamboo and the possible major synthesis sites of GA, screened for key genes in the crosstalk between auxin and GA, and laid the foundation for further exploration of the synergistic regulation of growth by GA and auxin in Moso bamboo.

Identification of GA2ox Family Genes and Expression Analysis under Gibberellin Treatment in Pineapple (Ananas comosus (L.) Merr.)

Gibberellin (GAs) plays an important regulatory role in the development and growth of pineapple (Ananas comosus (L.) Merr.). Bioinformatics was used to confirm the differential expression of GA2 gibberellin oxidase gene AcGA2oxs in the pineapple genome, which laid the foundation for exploring its role in pineapple. In this study, 42 GA2ox genes (AcGA2oxs) were identified in the pineapple genome, named from AcGA2ox1 to AcGA2ox42, and divided into four groups according to phylogenetic analysis. We also analyzed the gene structure, conserved motifs and chromosome localization of AcGA2oxs. AcGA2oxs within the same group had similar gene structure and motifs composition. Collinear analysis and cis-element analysis provided the basis for understanding the evolution and function of GA2ox genes in pineapple. In addition, we selected different tissue parts to analyze the expression profile of AcGA2oxs, and the results show that 41 genes were expressed, except for AcGA2ox18. AcGA2ox18 may not be expressed in these sites or may be pseudogenes. qRT-PCR (real-time fluorescence quantitative PCR) was used to detect the relative expression levels of the GA2ox gene family under different concentrations of GA3 treatment, and it was found that AcGA2ox gene expression was upregulated in different degrees under GA3 treatment. These results provide useful information for further study on the evolution and function of the GA2ox family in pineapple.

Integrated morphological, metabolome, and transcriptome analyses revealed the mechanism of exogenous gibberellin promoting petiole elongation in Oenanthe javanica

Oenanthe javanica (Blume) DC. is a popular vegetable with unique flavor and its leaf is the main product organ. Gibberellin (GA) is an important plant hormone that plays vital roles in regulating the growth of plants. In this study, the plants of water dropwort were treated with different concentrations of GA₃. The plant height of water dropwort was significantly increased after GA₃ treatment. Anatomical structure analysis indicated that the cell length of water dropwort was elongated under exogenous application of GA₃. The metabolome analysis showed flavonoids were the most abundant metabolites and the biosynthesis of secondary metabolites were also regulated by GA₃. The exogenous application of GA₃ altered the gene expressions of plant hormone signal transduction (GID and DELLA) and metabolites biosynthesis pathways to regulate the growth of water dropwort. The GA contents were modulated by up-regulating the expression of GA metabolism gene GA2ox. The differentially expressed genes related to cell wall formation were significantly enriched. A total of 22 cellulose synthase involved in cellulose biosynthesis were identified from the genome of water dropwort. Our results indicated that GA treatment promoted the cell elongation by inducing the expression of cellulose synthase and cell wall formation in water dropwort. These results revealed the molecular mechanism of GA-mediated cell elongation, which will provide valuable reference for using GA to regulate the growth of water dropwort.

Characterization and the comprehensive expression analysis of tobacco valine-glutamine genes in response to trichomes development and stress tolerance

Valine-glutamine genes (VQ) acted as transcription regulators and played the important roles in plant growth and development, and stress tolerance through interacting with transcription factors and other co-regulators. In this study, sixty-one VQ genes containing the FxxxVQxxTG motif were identified and updated in the Nicotiana tobacum genome. Phylogenetic analysis indicated that NtVQ genes were divided into seven groups and genes of each group had highly conserved exon-intron structure. Expression patterns analysis firstly showed that NtVQ genes expressed individually in different tobacco tissues including mixed-trichome (mT), glandular-trichome (gT), and nonglandular-trichome (nT), and the expression levels were also distinguishing in response to methyl jasmonate (MeJA), salicylic acid (SA), gibberellic acid (GA), ethylene (ETH), high salinity and PEG stresses. Besides, only NtVQ17 of its gene family was verified to have acquired autoactivating activity. This work will not only lead a foundation on revealing the functions of NtVQ genes in tobacco trichomes but also provided references to VQ genes related stress tolerance research in more crops.

Ent-kaurane diterpenoids from the Annonaceae family: a review of research progress and call for further research

The Annonaceae is one of the plant families with members that are credited with numerous pharmacological functions. Among the group of compounds responsible for these bioactivities are the ent-kaurane diterpenoids. The ent-kauranes are a group of 20-Carbon, tetracyclic diterpenoids that are widely distributed in other plant families including the Annonaceae family. This mini-review focuses mainly on the ent-kaurane diterpenoids isolated from the Annonaceae family, delineates the various biological activities of these compounds, and highlights the research gaps that exist for further scientific scrutiny.

Domestication has altered the ABA and gibberellin profiles in developing pea seeds

MAIN CONCLUSION

We showed that wild pea seeds contained a more diverse combination of bioactive GAs and had higher ABA content than domesticated peas. Although the role of abscisic acid (ABA) and gibberellins (GAs) interplay has been extensively studied in Arabidopsis and cereals models, comparatively little is known about the effect of domestication on the level of phytohormones in legume seeds. In legumes, as in other crops, seed dormancy has been largely or entirely removed during domestication. In this study, we have measured the endogenous levels of ABA and GAs comparatively between wild and domesticated pea seeds during their development. We have shown that wild seeds contained more ABA than domesticated ones, which could be important for preparing the seeds for the period of dormancy. ABA was catabolised particularly by an 8´-hydroxylation pathway, and dihydrophaseic acid was the main catabolite in seed coats as well as embryos. Besides, the seed coats of wild and pigmented cultivated genotypes were characterised by a broader spectrum of bioactive GAs compared to non-pigmented domesticated seeds. GAs in both seed coat and embryo were synthesized mainly by a 13-hydroxylation pathway, with GA29 being the most abundant in the seed coat and GA20 in the embryos. Measuring seed water content and water loss indicated domesticated pea seeds´ desiccation was slower than that of wild pea seeds. Altogether, we showed that pea domestication led to a change in bioactive GA composition and a lower ABA content during seed development.

The plant protection preparation GZM improves crop immunity, yield, and quality

Lauryl alcohol, a natural compound found in plants and other organisms, is widely used to make surfactants, food, and pharmaceuticals. GZM, a plant protection preparation with lauryl alcohol as its major component is thought to establish a physical barrier on the plant surface, but its physiological functions are unknown. Here, we show that GZM improves the performance of peanut (Arachis hypogaea) plants in both the laboratory and the field. We demonstrate that the treatment with GZM or lauryl alcohol raises the contents of several specific lysophospholipids and induces the biosynthesis of phenylpropanoids, flavonoids, and wax in various plant species. In the field, GZM improves crop immunity, yield, and quality. In addition, GZM and lauryl alcohol can inhibit the growth of some pathogenic fungi. Our findings provide insights into the physiological and biological effects of GZM treatment on plants and show that GZM and lauryl alcohol are promising preparations in agricultural production.

Bacillus velezensis Strain HN-Q-8 Induced Resistance to Alternaria solani and Stimulated Growth of Potato Plant

Bacillus velezensis HN-Q-8, isolated in our previous study, has an antagonistic effect on Alternaria solani. After being pretreated with a fermentation liquid with HN-Q-8 bacterial cell suspensions, the potato leaves inoculated with A. solani displayed smaller lesion areas and less yellowing than the controls. Interestingly, the activity levels of superoxide dismutase, peroxidase, and catalase in potato seedlings were enhanced by the addition of the fermentation liquid with bacterial cells. Additionally, the overexpression of key genes related to induced resistance in the Jasmonate/Ethylene pathway was activated by the addition of the fermentation liquid, suggesting that the HN-Q-8 strain induced resistance to potato early blight. In addition, our laboratory and field experiments showed that the HN-Q-8 strain can promote potato seedling growth and significantly increase tuber yield. The root activity and chlorophyll content of potato seedlings were significantly increased along with the levels of indole acetic acid, gibberellic acid 3, and abscisic acid upon addition of the HN-Q-8 strain. The fermentation liquid with bacterial cells was more efficient in inducing disease resistance and promoting growth than bacterial cell suspensions alone or the fermentation liquid without bacterial cells. Thus, the B. velezensis HN-Q-8 strain is an effective bacterial biocontrol agent, augmenting the options available for potato cultivation.

ZmCIPK32 positively regulates germination of stressed seeds via gibberellin signal

Calcineurin B-like proteins (CBLs) as specific calcium sensors that interact with CBL-interacting protein kinases (CIPKs) play a key role in the regulation of plant development and abiotic stress tolerance. In this study, we isolated and characterized the CIPK32 gene from Zea mays. ZmCIPK32 showed that it comprised 440 amino acids and a conserved NAF motif responsible for the interaction with CBLs localized in the cytoplasm and cell membrane. The interaction of ZmCIPK32 with ZmCBL1 and ZmCBL9 demonstrated using yeast two-hybrid system and bimolecular fluorescence complementation assay required the presence of the NAF domain. Overexpression of ZmCIPK32 promoted early germination in transgenic Arabidopsis seeds relative to that observed in wild-type (WT) plants under mannitol treatment. In addition, ZmCIPK32-overexpressing plants were insensitive to treatments with exogenous abscisic acid and paclobutrazol (PBZ) at seed germination and early seedling stages. Expression levels of the key genes GA20ox and GA3ox involved in the synthesis of gibberellin (GA) were increased, whereas expression levels of genes involved in the conversion of active GA to inactive forms and GA signaling were reduced in ZmCIPK32-overexpressing plants relative to those in WT plants under mannitol and PBZ treatments. Furthermore, overexpression of ZmCIPK32 increased GA level but decreased abscisic acid level in transgenic lines compared to the respective levels in WT plants under PBZ or mannitol treatments. Our results suggest that ZmCIPK32 positively regulates seed germination under stressed conditions by modulating GA signals.

Tomato sucrose transporter SlSUT4 participates in flowering regulation by modulating gibberellin biosynthesis

The functions of sucrose transporters (SUTs) differ among family members. The physiological function of SUT1 has been studied intensively, while that of SUT4 in various plant species including tomato (Solanum lycopersicum) is less well-understood. In this study, we characterized the function of tomato SlSUT4 in the regulation of flowering using a combination of molecular and physiological analyses. SlSUT4 displayed transport activity for sucrose when expressed in yeast (Saccharomyces cerevisiae), and it localized at both the plasma membrane and tonoplast. SlSUT4 interacted with SlSUT1, causing partial internalization of the latter, the main phloem loader of sucrose in tomato. Silencing of SlSUT4 promoted SlSUT1 localization to the plasma membrane, contributing to increased sucrose export and thus increased sucrose level in the shoot apex, which promoted flowering. Both silencing of SlSUT4 and spraying with sucrose suppressed gibberellin biosynthesis through repression of ent-kaurene oxidase and gibberellin 20-oxidase-1 (2 genes encoding key enzymes in gibberellin biosynthesis) expression by SlMYB76, which directly bound to their promoters. Silencing of SlMYB76 promoted gibberellin biosynthesis. Our results suggest that SlSUT4 is a functional SUT in tomato; downregulation of SlSUT4 expression enhances sucrose transport to the shoot apex, which promotes flowering by inhibiting gibberellin biosynthesis.

Calcium-binding protein OsANN1 regulates rice blast disease resistance by inactivating jasmonic acid signaling

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is one of the most devastating diseases in rice (Oryza sativa L.). Plant annexins are calcium- and lipid-binding proteins that have multiple functions; however, the biological roles of annexins in plant disease resistance remain unknown. Here, we report a rice annexin gene, OsANN1 (Rice annexin 1), that was induced by M. oryzae infection and negatively regulated blast disease resistance in rice. By yeast 2-hybrid screening, we found that OsANN1 interacted with a cytochrome P450 monooxygenase, HAN1 ("HAN" termed "chilling" in Chinese), which has been reported to catalyze the conversion of biologically active jasmonoyl-L-isoleucine (JA-Ile) to the inactive form 12-hydroxy-JA-Ile. Pathogen inoculation assays revealed that HAN1 was also a negative regulator in rice blast resistance. Genetic evidence showed that OsANN1 acts upstream of HAN1. OsANN1 stabilizes HAN1 in planta, resulting in the inactivation of the endogenous biologically active JA-Ile. Taken together, our study unravels a mechanism where an OsANN1-HAN1 module impairs blast disease resistance via inactivating biologically active JA-Ile and JA signaling in rice.

Seed dormancy loss from dry after-ripening is associated with increasing gibberellin hormone levels in Arabidopsis thaliana

Introduction

The seeds of many plants are dormant and unable to germinate at maturity, but gain the ability to germinate through after-ripening during dry storage. The hormone abscisic acid (ABA) stimulates seed dormancy, whereas gibberellin A (GA) stimulates dormancy loss and germination.

Methods

To determine whether dry after-ripening alters the potential to accumulate ABA and GA, hormone levels were measured during an after-ripening time course in dry and imbibing ungerminated seeds of wildtype Landsberg erecta (Ler) and of the highly dormant GA-insensitive mutant sleepy1-2 (sly1-2).

Results

The elevated sly1-2 dormancy was associated with lower rather than higher ABA levels. Ler germination increased with 2-4 weeks of after-ripening whereas sly1-2 required 21 months to after-ripen. Increasing germination capacity with after-ripening was associated with increasing GA₄ levels in imbibing sly1-2 and wild-type Ler seeds. During the same 12 hr imbibition period, after-ripening also resulted in increased ABA levels.

Discussion

The decreased ABA levels with after-ripening in other studies occurred later in imbibition, just before germination. This suggests a model where GA acts first, stimulating germination before ABA levels decline, and ABA acts as the final checkpoint preventing germination until processes essential to survival, like DNA repair and activation of respiration, are completed. Overexpression of the GA receptor GID1b (GA INSENSITIVE DWARF1b) was associated with increased germination of sly1-2 but decreased germination of wildtype Ler. This reduction of Ler germination was not associated with increased ABA levels. Apparently, GID1b is a positive regulator of germination in one context, but a negative regulator in the other.

Advances in Rice Seed Shattering

Seed shattering is an important trait that wild rice uses to adapt to the natural environment and maintain population reproduction, and weedy rice also uses it to compete with the rice crop. The loss of shattering is a key event in rice domestication. The degree of shattering is not only one of the main reasons for rice yield reduction but also affects its adaptability to modern mechanical harvesting methods. Therefore, it is important to cultivate rice varieties with a moderate shattering degree. In this paper, the research progress on rice seed shattering in recent years is reviewed, including the physiological basis, morphological and anatomical characteristics of rice seed shattering, inheritance and QTL/gene mapping of rice seed shattering, the molecular mechanism regulating rice seed shattering, the application of seed-shattering genes, and the relationship between seed-shattering genes and domestication.

Genome-wide identification, evolution and expression profiles analysis of bHLH gene family in Castanea mollissima

The basic helix-loop-helix (bHLH) transcription factors (TFs) gene family is an important gene family in plants, and participates in regulation of plant apical meristem growth, metabolic regulation and stress resistance. However, its characteristics and potential functions have not been studied in chestnut (Castanea mollissima), an important nut with high ecological and economic value. In the present study, 94 CmbHLHs were identified in chestnut genome, of which 88 were unevenly distributed on chromosomes, and other six were located on five unanchored scaffolds. Almost all CmbHLH proteins were predicted in the nucleus, and subcellular localization demonstrated the correctness of the above predictions. Based on the phylogenetic analysis, all of the CmbHLH genes were divided into 19 subgroups with distinct features. Abundant cis-acting regulatory elements related to endosperm expression, meristem expression, and responses to gibberellin (GA) and auxin were identified in the upstream sequences of CmbHLH genes. This indicates that these genes may have potential functions in the morphogenesis of chestnut. Comparative genome analysis showed that dispersed duplication was the main driving force for the expansion of the CmbHLH gene family inferred to have evolved through purifying selection. Transcriptome analysis and qRT-PCR experiments showed that the expression patterns of CmbHLHs were different in different chestnut tissues, and revealed some members may have potential functions in chestnut buds, nuts, fertile/abortive ovules development. The results from this study will be helpful to understand the characteristics and potential functions of the bHLH gene family in chestnut.

Multiomics strategies for decoding seed dormancy breakdown in Paris polyphylla

BACKGROUND

The disruption of seed dormancy is a complicated process and is controlled by various factors. Among these factors, membrane lipids and plant hormones are two of the most important ones. Paris polyphylla is an important Chinese herbaceous species, and the dormancy trait of its seed limits the cultivation of this herb.

RESULTS

In this study, we investigate the global metabolic and transcriptomic profiles of Paris polyphylla during seed dormancy breaking. Widely targeted metabolomics revealed that lysophospholipids (lysoPLs) increased during P. polyphylla seed dormancy breaking. The expression of phospholipase A2 (PLA2), genes correlated to the production of lysoPLs, up-regulated significantly during this process. Abscisic acid (ABA) decreased dramatically during seed dormancy breaking of P. polyphylla. Changes of different GAs varied during P. polyphylla seeds dormancy breaking, 13-OH GAs, such as GA₅₃ were not detected, and GA₃ decreased significantly, whereas 13-H GAs, such as GA₁₅, GA₂₄ and GA₄ increased. The expression of CYP707As was not synchronous with the change of ABA content, and the expression of most UGTs, GA20ox and GA3ox up-regulated during seed dormancy breaking.

CONCLUSIONS

These results suggest that PLA2 mediated production of lysoPLs may correlate to the seed dormancy breaking of P. polyphylla. The conversion of ABA to ABA-GE catalysed by UGTs may be the main cause of ABA degradation. Through inhibition the expression of genes related to the synthesis of 13-OH GAs and up-regulation genes related to the synthesis of 13-H GAs, P. polyphylla synthesized more bioactive 13-H GA (GA₄) to break its seed dormancy.

Identification of a new gibberellin receptor agonist, diphegaractin, by a cell-free chemical screening system

Gibberellin (GA) is a phytohormone that regulates various developmental processes during the plant life cycle. In this study, we identify a new GA agonist, diphegaractin, using a wheat cell-free based drug screening system with grape GA receptor. A GA-dependent interaction assay system using GA receptors and DELLA proteins from Vitis vinifera was constructed using AlphaScreen technology and cell-free produced proteins. From the chemical compound library, diphegaractin was found to enhance the interactions between GA receptors and DELLA proteins from grape in vitro. In grapes, we found that diphegaractin induces elongation of the bunch and increases the sugar concentration of grape berries. Furthermore, diphegaractin shows GA-like activity, including promotion of root elongation in lettuce and Arabidopsis, as well as reducing peel pigmentation and suppressing peel puffing in citrus fruit. To the best of our knowledge, this study is the first to successfully identify a GA receptor agonist showing GA-like activity in agricultural plants using an in vitro molecular-targeted drug screening system.

Comparative transcriptome profiling reveals the multiple levels of crosstalk in phytohormone networks in Brassica napus

Plant hormones are the intrinsic factors that control plant development. The integration of different phytohormone pathways in a complex network of synergistic, antagonistic and additive interactions has been elucidated in model plants. However, the systemic level of transcriptional responses to hormone crosstalk in Brassica napus is largely unknown. Here, we present an in-depth temporal-resolution study of the transcriptomes of the seven hormones in B. napus seedlings. Differentially expressed gene analysis revealed few common target genes that co-regulated (up- and down-regulated) by seven hormones; instead, different hormones appear to regulate distinct members of protein families. We then constructed the regulatory networks between the seven hormones side by side, which allowed us to identify key genes and transcription factors that regulate the hormone crosstalk in B. napus. Using this dataset, we uncovered a novel crosstalk between gibberellin and cytokinin in which cytokinin homeostasis was mediated by RGA-related CKXs expression. Moreover, the modulation of gibberellin metabolism by the identified key transcription factors was confirmed in B. napus. Furthermore, all data were available online from http://yanglab.hzau.edu.cn/BnTIR/hormone. Our study reveals an integrated hormone crosstalk network in Brassica napus, which also provides a versatile resource for future hormone studies in plant species.

Transcription elongation factors OsSPT4 and OsSPT5 are essential for rice growth and development and act with APO2

KEY MESSAGE

The transcription elongation factor SPT4/SPT5 complex is essential for rice vegetative and reproductive growth and that OsSPT5-1, with its interactor APO2, is involved in multiple phytohormone pathways. The SPT4/SPT5 complex is a transcription elongation factor that regulates the processivity of transcription elongation. However, our understanding of the role of SPT4/SPT5 complex in developmental regulation remains limited. Here, we identified three SPT4/SPT5 genes (OsSPT4, OsSPT5-1, and OsSPT5-2) in rice, and investigated their roles in vegetative and reproductive growth. These genes are highly conserved with their orthologs in other species. OsSPT4 and OsSPT5-1 are widely expressed in various tissues. By contrast, OsSPT5-2 is expressed at a relatively low level, which could cause osspt5-2 null mutants have no phenotypes. Loss-of-function mutants of OsSPT4 and OsSPT5-1 could not be obtained; their heterozygotes showed severe reproductive growth defects. An incomplete mutant line (osspt5-1#12) displayed gibberellin-related dwarfed defects and a weak root system at an early vegetative phase, and a short life cycle in different planting environments. Furthermore, OsSPT5-1 interacts with the transcription factor ABERRANT PANICLE ORGANIZATION 2 (APO2) and plays a similar role in regulating the growth of rice shoots. RNA sequencing analysis verified that OsSPT5-1 is involved in multiple phytohormone pathways, including gibberellin, auxin, and cytokinin. Therefore, the SPT4/SPT5 complex is essential for both vegetative and reproductive growth in rice.

A Wox3-patterning module organizes planar growth in grass leaves and ligules

Grass leaves develop from a ring of primordial initial cells within the periphery of the shoot apical meristem, a pool of organogenic stem cells that generates all of the organs of the plant shoot. At maturity, the grass leaf is a flattened, strap-like organ comprising a proximal supportive sheath surrounding the stem and a distal photosynthetic blade. The sheath and blade are partitioned by a hinge-like auricle and the ligule, a fringe of epidermally derived tissue that grows from the adaxial (top) leaf surface. Together, the ligule and auricle comprise morphological novelties that are specific to grass leaves. Understanding how the planar outgrowth of grass leaves and their adjoining ligules is genetically controlled can yield insight into their evolutionary origins. Here we use single-cell RNA-sequencing analyses to identify a 'rim' cell type present at the margins of maize leaf primordia. Cells in the leaf rim have a distinctive identity and share transcriptional signatures with proliferating ligule cells, suggesting that a shared developmental genetic programme patterns both leaves and ligules. Moreover, we show that rim function is regulated by genetically redundant Wuschel-like homeobox3 (WOX3) transcription factors. Higher-order mutations in maize Wox3 genes greatly reduce leaf width and disrupt ligule outgrowth and patterning. Together, these findings illustrate the generalizable use of a rim domain during planar growth of maize leaves and ligules, and suggest a parsimonious model for the homology of the grass ligule as a distal extension of the leaf sheath margin.

PsRGL1 negatively regulates chilling- and gibberellin-induced dormancy release by PsF-box1-mediated targeting for proteolytic degradation in tree peony

Tree peony bud endodormancy is a common survival strategy similar to many perennial woody plants in winter, and the activation of the GA signaling pathway is the key to breaking endodormancy. GA signal transduction is involved in many physiological processes. Although the GA-GID1-DELLA regulatory module is conserved in many plants, it has a set of specific components that add complexity to the GA response mechanism. DELLA proteins are key switches in GA signaling. Therefore, there is an urgent need to identify the key DELLA proteins involved in tree peony bud dormancy release. In this study, the prolonged chilling increased the content of endogenously active gibberellins. PsRGL1 among three DELLA proteins was significantly downregulated during chilling- and exogenous GA3-induced bud dormancy release by cell-free degradation assay, and a high level of polyubiquitination was detected. Silencing PsRGL1 accelerated bud dormancy release by increasing the expression of the genes associated with dormancy release, including PsCYCD, PsEBB1, PsEBB3, PsBG6, and PsBG9. Three F-box protein family members responded to chilling and GA3 treatments, resulting in PsF-box1 induction. Yeast two-hybrid and BiFC assays indicated that only PsF-box1 could bind to PsRGL1, and the binding site was in the C-terminal domain. PsF-box1 overexpression promoted dormancy release and upregulated the expression of the dormancy-related genes. In addition, yeast two-hybrid and pull-down assays showed that PsF-box1 also interacted with PsSKP1 to form an E3 ubiquitin ligase. These findings enriched the molecular mechanism of the GA signaling pathway during dormancy release, and enhanced the understanding of tree peony bud endodormancy.

OsNF-YA3 regulates plant growth and osmotic stress tolerance by interacting with SLR1 and SAPK9 in rice

The antagonism between gibberellin (GA) and abscisic acid (ABA) signaling pathways is vital to balance plant growth and stress response. Nevertheless, the mechanism by which plants determine the balance remains to be elucidated. Here, we report that rice NUCLEAR FACTOR-Y A3 (OsNF-YA3) modulates GA- and ABA-mediated balance between plant growth and osmotic stress tolerance. OsNF-YA3 loss-of-function mutants exhibit stunted growth, compromised GA biosynthetic gene expression, and decreased GA levels, while its overexpression lines have promoted growth and enhanced GA content. Chromatin immunoprecipitation-quantitative polymerase chain reaction analysis and transient transcriptional regulation assays demonstrate that OsNF-YA3 activates GA biosynthetic gene OsGA20ox1 expression. Furthermore, the DELLA protein SLENDER RICE1 (SLR1) physically interacts with OsNF-YA3 and thus inhibits its transcriptional activity. On the other side, OsNF-YA3 negatively regulates plant osmotic stress tolerance by repressing ABA response. OsNF-YA3 reduces ABA levels by transcriptionally regulating ABA catabolic genes OsABA8ox1 and OsABA8ox3 by binding to their promoters. Furthermore, OSMOTIC STRESS/ABA-ACTIVATED PROTEIN KINASE 9 (SAPK9), the positive component in ABA signaling, interacts with OsNF-YA3 and mediates OsNF-YA3 phosphorylation, resulting in its degradation in plants. Collectively, our findings establish OsNF-YA3 as an important transcription factor that positively modulates GA-regulated plant growth and negatively controls ABA-mediated water-deficit and salt tolerance. These findings shed light on the molecular mechanism underlying the balance between the growth and stress response of the plant.

Analysis of morphological traits and regulatory mechanism of a semi-dwarf, albino, and blue grain wheat line

The plant height and leaf color are important traits in crops since they contribute to the production of grains and biomass. Progress has been made in mapping the genes that regulate plant height and leaf color in wheat (Triticum aestivum L.) and other crops. Wheat line DW-B (dwarfing, white leaves, and blue grains) with semi-dwarfing and albinism at the tillering stage and re-greening at the jointing stage was created using Lango and Indian Blue Grain. Transcriptomic analyses of the three wheat lines at the early jointing stages indicated that the genes of gibberellin (GA) signaling pathway and chlorophyll (Chl) biosynthesis were expressed differently in DW-B and its parents. Furthermore, the response to GA and Chl contents differed between DW-B and its parents. The dwarfing and albinism in DW-B were owing to defects in the GA signaling pathway and abnormal chloroplast development. This study can improve understanding of the regulation of plant height and leaf color.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01379-z.

Heterologous functional analysis and expression patterns of gibberellin 2-oxidase genes of barley (Hordeum vulgare L.)

The level of bioactive gibberellins (GAs) in plants is regulated partly by their inactivation, mainly by the action of GA 2-oxidases (GA2oxs). This study identified three new GA2ox genes in barley: HvGA2ox1, HvGA2ox3 and HvGA2ox6. Analysis of their nucleotide and putative amino acid sequences revealed that they share high sequence identity with other plant GA2oxs and their corresponding proteins. Phylogenetic analysis revealed the HvGA2ox1, HvGA2ox3 and HvGA2ox6 belong to GA2ox structural classes II, I, and III, respectively. Feeding the HvGA2ox1 and HvGA2ox3 recombinant proteins with the C19-GAs, GA₁ and GA₂₀, resulted in the production of GA₈ and GA₂₉, respectively, with no product detected when they were fed with the C20-GA, GA₁₂. Whereas the HvGA2ox6 recombinant protein was able to convert GA₁₂ to GA₁₁₀, and no product was detected when it was fed with GA₁ or GA₂₀. HvGA2ox1 and HvGA2ox3 were highly expressed in internodes and the endosperm of maturing seeds while HvGA2ox6 was predominantly expressed in the embryos. Salinity stress upregulated the expression of all three genes in seedling tissues. Our results indicate that HvGA2ox1, HvGA2ox3 and HvGA2ox6 encode functional GA2oxs that can regulate GA levels, and therefore growth and development of a barley plant, and its interaction with environment.