A Century of Gibberellin Research

Modeling vegetative vigour in grapevine: unraveling underlying mechanisms

Mechanistic modeling constitutes a powerful tool to unravel complex biological phenomena. This study describes the construction of a mechanistic, dynamic model for grapevine plant growth and canopy biomass (vigor). To parametrize and validate the model, the progeny from a cross of Ramsey (Vitis champinii) × Riparia Gloire (V. riparia) was evaluated. Plants with different vigor were grown in a greenhouse during the summer of 2014 and 2015. One set of plants was grafted with Cabernet Sauvignon. Shoot growth rate (b), leaf area (LA), dry biomass, whole plant and root specific hydraulic conductance (k_H and L_pr), stomatal conductance (g_s), and water potential (Ψ) were measured. Partitioning indices and specific leaf area (SLA) were calculated. The model includes an empirical fit of a purported seasonal pattern of bioactive GAs based on published seasonal evolutionary levels and reference values. The model provided a good fit of the experimental data, with R = 0.85. Simulation of single trait variations defined the individual effect of each variable on vigor determination. The model predicts, with acceptable accuracy, the vigor of a young plant through the measurement of L_pr and SLA. The model also permits further understanding of the functional traits that govern vigor, and, ultimately, could be considered useful for growers, breeders and those studying climate change.

The Importance of Earth Reference Controls in Spaceflight -Omics Research: Characterization of Nucleolin Mutants from the Seedling Growth Experiments

Understanding plant adaptive responses to the space environment is a requisite for enabling space farming. Spaceflight produces deleterious effects on plant cells, particularly affecting ribosome biogenesis, a complex stress-sensitive process coordinated with cell division and differentiation, known to be activated by red light. Here, in a series of ground studies, we have used mutants from the two Arabidopsis nucleolin genes (NUC1 and NUC2, nucleolar regulators of ribosome biogenesis) to better understand their role in adaptive response mechanisms to stress on Earth. Thus, we show that nucleolin stress-related gene NUC2 can compensate for the environmental stress provided by darkness in nuc1 plants, whereas nuc2 plants are not able to provide a complete response to red light. These ground control findings, as part of the ESA/NASA Seedling Growth spaceflight experiments, will determine the basis for the identification of genetic backgrounds enabling an adaptive advantage for plants in future space experiments.

Comparison of Soaking Corms with Moringa Leaf Extract Alone or in Combination with Synthetic Plant Growth Regulators on the Growth, Physiology and Vase Life of Sword Lily

Gladiolus is in demand worldwide as a cut-flower or landscaping plant, because of its superior commercial and ornamental value. Application of plant-based biostimulants has gained interest in the horticulture industry as an innovative and promising approach to ensure enhanced and sustainable yields along with better product quality. The influence of pre-plant corm soaks supplemented to 5% (v/v) with an aqueous extract from Moringa oleifera leaves (MLE) either alone or in combination with 50 mg/L salicylic acid (SA) or 50 mg/L gibberellic acid (GA) on the vegetative, physiological, and ornamental characteristics of potted gladiolus (Gladiolus grandiflorus) was investigated. In general, the treatment order for greatest horticultural value for all the parameters examined was: MLE + SA + GA > MLE + GA or SA individually > MLE alone > water-only control. Compared to other treatments, corms soaked in MLE + SA + GA had the earliest sprout time (3.7 days earlier than control), shortest production time (11 days earlier than control), tallest plant (159.5 cm), greatest number of leaves per plant (8.85 leaves), greatest maximum leaf area (66 cm²), highest SPAD reading (112) and photosynthetic activity (6.7 mmol m^-2 s^-1), longest spike length (91 cm), greatest number of florets per spike (20 florets), longest vase life (14.8 days), greatest N (1.53%), P (0.28%), and K (0.64%) concentrations, and largest corm diameter (4.68 cm) and mass (22.25 g). The highest total protein and proline concentrations were observed with the combined application of MLE + GA + SA. Our findings suggested that MLE either alone or in combination with other plant growth regulators not only increased the yield and quality of cut spikes, but also prolonged the vase life of cut gladiolus.

Small grain and semi-dwarf 3, a WRKY transcription factor, negatively regulates plant height and grain size by stabilizing SLR1 expression in rice

OsWRKY36 represses plant height and grain size by inhibiting gibberellin signaling. Plant height and grain size are important agronomic traits affecting yield in cereals, including rice. Gibberellins (GAs) are plant hormones that promote plant growth and developmental processions such as stem elongation and grain size. WRKYs are transcription factors that regulate stress tolerance and plant development including height and grain size. However, the relationship between GA signaling and WRKY genes is still poorly understood. Here, we characterized a small grain and semi-dwarf 3 (sgsd3) mutant in rice cv. Hwayoung (WT). A T-DNA insertion in the 5'-UTR of OsWRKY36 induced overexpression of OsWRKY36 in the sgsd3 mutant, likely leading to the mutant phenotype. This was confirmed by the finding that overexpression of OsWRKY36 caused a similar small grain and semi-dwarf phenotype to the sgsd3 mutant whereas knock down and knock out caused larger grain phenotypes. The sgsd3 mutant was also hyposensitive to GA and accumulated higher mRNA and protein levels of SLR1 (a GA signaling DELLA-like inhibitor) compared with the WT. Further assays showed that OsWRKY36 enhanced SLR1 transcription by directly binding to its promoter. In addition, we found that OsWRKY36 can protect SLR1 from GA-mediated degradation. We thus identified a new GA signaling repressor OsWRKY36 that represses GA signaling through stabilizing the expression of SLR1.

Enhanced Activity of Genes Associated With Photosynthesis, Phytohormone Metabolism and Cell Wall Synthesis Is Involved in Gibberellin-Mediated Sugarcane Internode Growth

Internode elongation is an important trait in sugarcane as it affects the sugarcane yield. Gibberellin (GA) is a key modulator of internode elongation in sugarcane. Understanding the gene expression features of GA-mediated internode elongation has both scientific and practical significance. This study aimed to examine the transcriptomic changes in the internode elongation of sugarcane following GA treatment. Eighteen cDNA libraries from the internode tissues on days of 0, 3, and 6 in control and GA treatment groups were sequenced and their gene expression were studied. RNA-seq analysis revealed 1,338,723,248 reads and 70,821 unigenes from elongating internodes of sugarcane. Comparative studies discovered a large number of transcripts that were differentially expressed in GA-treated samples compared to the control. Further analysis revealed that the differentially expressed genes were enriched in the metabolic process, one-carbon compound transport, and single-organism process. Kyoto Encyclopedia of Genes and Genomes pathway annotation showed significant enrichment in photosynthesis and plant hormone signal transduction, indicating its involvement in internode elongation. The function analysis suggested that metabolic pathways and biosynthesis of secondary metabolites, plant hormones, and cell wall components were enriched in the internodes of the GA-treated plants. The hub genes were identified, with the function of cellulose synthesis. The results of this study provide a global view of mRNA changes during sugarcane internode elongation and extend our knowledge of the GA-mediated cellular processes involved in sugarcane stem growth.

Identification of epigenetic variation associated with synchronous pod maturity in mungbean (Vigna radiata L.)

Cytosine methylation in genomic DNA affects gene expression, potentially causing phenotypic variation. Mungbean, an agronomically and nutritionally important legume species, is characterized by nonsynchronous pod maturity, resulting in multiple harvest which costs extra time and labor. To elucidate the epigenetic influences on synchronous pod maturity (SPM) in mungbean, we determined the genome-wide DNA methylation profiles of eight mungbean recombinant inbred lines (RILs) and their parental genotypes, and compared DNA methylation profiles between high SPM and low SPM RILs, thus revealing differentially methylated regions (DMRs). A total of 3, 18, and 28 pure DMRs, defined as regions showing no significant correlation between nucleotide sequence variation and methylation level, were identified in CpG, CHG, and CHH contexts, respectively. These DMRs were proximal to 20 genes. Among the 544 single nucleotide polymorphisms identified near the 20 genes, only one caused critical change in gene expression by early termination. Analysis of these genome-wide DNA methylation profiles suggests that epigenetic changes can influence the expression of proximal genes, regardless of nucleotide sequence variation, and that SPM is mediated through gibberellin-mediated hormone signaling pathways. These results provide insights into how epialleles contribute to phenotypic variation and improve SPM in mungbean cultivars.

Systematic Analysis of Gibberellin Pathway Components in Medicago truncatula Reveals the Potential Application of Gibberellin in Biomass Improvement

Gibberellins (GAs), a class of phytohormones, act as an essential natural regulator of plant growth and development. Many studies have shown that GA is related to rhizobial infection and nodule organogenesis in legume species. However, thus far, GA metabolism and signaling components are largely unknown in the model legume Medicago truncatula. In this study, a genome-wide analysis of GA metabolism and signaling genes was carried out. In total 29 components, including 8 MtGA20ox genes, 2 MtGA3ox genes, 13 MtGA2ox genes, 3 MtGID1 genes, and 3 MtDELLA genes were identified in M. truncatula genome. Expression profiles revealed that most members of MtGAox, MtGID1, and MtDELLA showed tissue-specific expression patterns. In addition, the GA biosynthesis and deactivation genes displayed a feedback regulation on GA treatment, respectively. Yeast two-hybrid assays showed that all the three MtGID1s interacted with MtDELLA1 and MtDELLA2, suggesting that the MtGID1s are functional GA receptors. More importantly, M. truncatula exhibited increased plant height and biomass by ectopic expression of the MtGA20ox1, suggesting that enhanced GA response has the potential for forage improvement.

Emerging Connections between Small RNAs and Phytohormones

Small RNAs (sRNAs), mainly including miRNAs and siRNAs, are ubiquitous in eukaryotes. sRNAs mostly negatively regulate gene expression via (post-)transcriptional gene silencing through DNA methylation, mRNA cleavage, or translation inhibition. The mechanisms of sRNA biogenesis and function in diverse biological processes, as well as the interactions between sRNAs and environmental factors, like (a)biotic stress, have been deeply explored. Phytohormones are central in the plant's response to stress, and multiple recent studies highlight an emerging role for sRNAs in the direct response to, or the regulation of, plant hormonal pathways. In this review, we discuss recent progress on the unraveling of crossregulation between sRNAs and nine plant hormones.

Columnar growth phenotype in apple results from gibberellin deficiency by ectopic expression of a dioxygenase gene

The apple cultivar McIntosh Wijcik, which is a mutant of 'McIntosh', exhibits a columnar growth phenotype (short internodes, few lateral branches, many spurs, etc.) that is controlled by a dominant Co gene. The candidate gene (MdDOX-Co), encoding a 2-oxoglutarate-dependent dioxygenase, is located adjacent to an insertion mutation. Non-columnar apples express MdDOX-Co in the roots, whereas columnar apples express MdDOX-Co in the aerial parts as well as in the roots. However, the function of MdDOX-Co remains unknown. Here, we characterized tobacco plants overexpressing MdDOX-Co. The tobacco plants showed the typical dwarf phenotype, which was restored by application of gibberellin A3 (GA3). Moreover, the dwarf tobacco plants had low concentrations of endogenous bioactive gibberellin A1 (GA1) and gibberellin A4 (GA4). Similarly, 'McIntosh Wijcik' contained low endogenous GA4 concentration and its dwarf traits (short main shoot and internodes) were partially reversed by GA3 application. These results indicate that MdDOX-Co is associated with bioactive GA deficiency. Interestingly, GA3 application to apple trees also resulted in an increased number of lateral branches and a decrease in flower bud number, indicating that gibberellin (GA) plays important roles in regulating apple tree architecture by affecting both lateral branch formation (vegetative growth) and flower bud formation (reproductive growth). We propose that a deficiency of bioactive GA by ectopic expression of MdDOX-Co in the aerial parts of columnar apples not only induces dwarf phenotypes but also inhibits lateral branch development and promotes flower bud formation, and assembly of these multiple phenotypes constructs the columnar tree form.

Herbaceous peony (Paeonia lactiflora Pall.) PlDELLA gene negatively regulates dormancy release and plant growth

DELLA protein plays a significant role in plant growth and development. In this study, PlDELLA with the open reading frame of 1866 bp in length was isolated from Paeonia lactiflora. Overexpression of PlDELLA in Arabidopsis thaliana showed that seed germination was significantly repressed as it took 144∼192 h for the OEs to reach 100 % germination and it required only 60 h for the WT. The OEs were also inhibited in bolting time and in plant vegetative growth. When PlDELLA was silenced in peony by virus-induced gene silencing method, peony budbreak occurred earlier by 8∼10 d and the vegetative growth was significantly accelerated compared with the control group. These results collectively indicated that PlDELLA negatively regulated dormancy release and plant growth. During chilling process to release peony endodormancy, PlDELLA expression down-regulated, and the content of both endogenous active GAs and ABA decreased, indicating decreasing of PlDELLA expression under chilling was not caused by the known gibberellin signal transduction pathway. Besides, PlDELLA had no interaction with the four screened PlWRKYs, PlWRKY13, PlWRKY18, PlWRKY40 or PlWRKY50. These findings not only enrich the knowledge of DELLA protein family, but also provide insights into understanding the function of PlDELLA protein in endodormancy release in peony.

A quantitative trait locus GW6 controls rice grain size and yield through the gibberellin pathway

Grain size is one of the essential components determining rice yield and is a target for both domestication and artificial breeding. Gibberellins (GAs) are diterpenoid phytohormones that influence diverse aspects of plant growth and development. Several quantitative trait loci (QTLs) have been identified that control grain size through phytohormone regulation. However, little is known about the role of GAs in the control of grain size. Here we report the cloning and characterization of a QTL, GW6 (GRAIN WIDTH 6), which encodes a GA-regulated GAST family protein and positively regulates grain width and weight. GW6 is highly expressed in the young panicle and increases grain width by promoting cell expansion in the spikelet hull. Knockout of GW6 exhibits reduced grain size and weight, whereas overexpression of GW6 results in increased grain size and weight. GW6 is induced by GA and its knockout downregulates the expression of GA biosynthesis genes and decreases GA content in the young panicle. We found that a natural variation in the cis element CAAT-box in the promoter of GW6 is associated with its expression level and grain width and weight. Furthermore, introduction of GW6 to Oryza indica variety HJX74 can lead to a 10.44% increase in rice grain yield, indicating that GW6 has great potential to improve grain yield in rice.

Unraveling a Tangled Skein: Evolutionary Analysis of the Bacterial Gibberellin Biosynthetic Operon

Gibberellin (GA) phytohormones are ubiquitous regulators of growth and developmental processes in vascular plants. The convergent evolution of GA production by plant-associated bacteria, including both symbiotic nitrogen-fixing rhizobia and phytopathogens, suggests that manipulation of GA signaling is a powerful mechanism for microbes to gain an advantage in these interactions. Although orthologous operons encode GA biosynthetic enzymes in both rhizobia and phytopathogens, notable genetic heterogeneity and scattered operon distribution in these lineages, including loss of the gene for the final biosynthetic step in most rhizobia, suggest varied functions for GA in these distinct plant-microbe interactions. Therefore, deciphering GA operon evolutionary history should provide crucial evidence toward understanding the distinct biological roles for bacterial GA production. To further establish the genetic composition of the GA operon, two operon-associated genes that exhibit limited distribution among rhizobia were biochemically characterized, verifying their roles in GA biosynthesis. This enabled employment of a maximum parsimony ancestral gene block reconstruction algorithm to characterize loss, gain, and horizontal gene transfer (HGT) of GA operon genes within alphaproteobacterial rhizobia, which exhibit the most heterogeneity among the bacteria containing this biosynthetic gene cluster. Collectively, this evolutionary analysis reveals a complex history for HGT of the entire GA operon, as well as the individual genes therein, and ultimately provides a basis for linking genetic content to bacterial GA functions in diverse plant-microbe interactions, including insight into the subtleties of the coevolving molecular interactions between rhizobia and their leguminous host plants.IMPORTANCE While production of phytohormones by plant-associated microbes has long been appreciated, identification of the gibberellin (GA) biosynthetic operon in plant-associated bacteria has revealed surprising genetic heterogeneity. Notably, this heterogeneity seems to be associated with the lifestyle of the microbe; while the GA operon in phytopathogenic bacteria does not seem to vary to any significant degree, thus enabling production of bioactive GA, symbiotic rhizobia exhibit a number of GA operon gene loss and gain events. This suggests that a unique set of selective pressures are exerted on this biosynthetic gene cluster in rhizobia. Through analysis of the evolutionary history of the GA operon in alphaproteobacterial rhizobia, which display substantial diversity in their GA operon structure and gene content, we provide insight into the effect of lifestyle and host interactions on the production of this phytohormone by plant-associated bacteria.

An Updated Overview on the Regulation of Seed Germination

The ability of a seed to germinate and establish a plant at the right time of year is of vital importance from an ecological and economical point of view. Due to the fragility of these early growth stages, their swiftness and robustness will impact later developmental stages and crop yield. These traits are modulated by a continuous interaction between the genetic makeup of the plant and the environment from seed production to germination stages. In this review, we have summarized the established knowledge on the control of seed germination from a molecular and a genetic perspective. This serves as a “backbone” to integrate the latest developments in the field. These include the link of germination to events occurring in the mother plant influenced by the environment, the impact of changes in the chromatin landscape, the discovery of new players and new insights related to well-known master regulators. Finally, results from recent studies on hormone transport, signaling, and biophysical and mechanical tissue properties are underscoring the relevance of tissue-specific regulation and the interplay of signals in this crucial developmental process.

Molecular genetic analyses of abiotic stress responses during plant reproductive development

Plant responses to abiotic stresses during vegetative growth have been extensively studied for many years. Daily environmental fluctuations can have dramatic effects on plant vegetative growth at multiple levels, resulting in molecular, cellular, physiological, and morphological changes. Plants are even more sensitive to environmental changes during reproductive stages. However, much less is known about how plants respond to abiotic stresses during reproduction. Fortunately, recent advances in this field have begun to provide clues about these important processes, which promise further understanding and a potential contribution to maximize crop yield under adverse environments. Here we summarize information from several plants, focusing on the possible mechanisms that plants use to cope with different types of abiotic stresses during reproductive development, and present a tentative molecular portrait of plant acclimation during reproductive stages. Additionally, we discuss strategies that plants use to balance between survival and productivity, with some comparison among different plants that have adapted to distinct environments.

Tissue Culture and Refreshment Techniques for Improvement of Transformation in Local Tetraploid and Diploid Potato with Late Blight Resistance as an Example

Potato (Solanum tuberosum) is among the best producers of edible biomass in terms of yield per hectare and a variety of different regional cultivars are used as a staple commodity in many countries. However, this crop is attacked by several diseases, with the worst being the late blight disease caused by Phytophthora infestans. Stacking of resistance (R) genes from wild Solanum relatives are interesting prospects for the sustainable control of late blight. Therefore, we optimized methods for the efficient generation and screening of R-gene-containing transformants in tetraploid and diploid hybrid potato genotypes. Using these methods, a high transformation efficiency was achieved for the transformation of tetraploid and diploid potato lines with a triple resistance (3R) gene construct. Transformation efficiencies were improved by optimizing several factors affecting regeneration, including the quality of the starting plant material, and the composition of the plant growth regulators used during selective regeneration. A refreshment protocol was designed to alleviate in vitro related stress in stock plants, which significantly improved the growth vigor and resulted in a 4- to 10-fold increase in transformation efficiency. Furthermore, long-term exposure to exogenous Indole-3-butyric acid that is usually used for the initiation of roots in vitro, was found to cause aberrant morphological phenotypes in potato.

Recent advances in dissecting the demethylation reactions in natural product biosynthesis

Demethylation is a chemical process widely distributed in nature to remove a methyl group from an organic molecule, which is a key aspect of diverse biological processes including biosynthesis of natural products, degradation of plant biomass and epigenetic regulation. This process is facilitated by diverse demethylases via distinct mechanisms. Recent studies have disclosed some novel demethylation reactions as well as their underlying demethylases in the biosynthesis of bacterial sterols, fungal terpenoids, and plant alkaloids. This article focuses on current advances in dissecting the demethylation reactions in biosynthesis of natural products and aims to point out the enzymatic mechanisms, which will further enhance our knowledge and understanding of demethylation process in nature.

All Roads Lead to Auxin: Post-translational Regulation of Auxin Transport by Multiple Hormonal Pathways

Auxin is a key hormonal regulator, that governs plant growth and development in concert with other hormonal pathways. The unique feature of auxin is its polar, cell-to-cell transport that leads to the formation of local auxin maxima and gradients, which coordinate initiation and patterning of plant organs. The molecular machinery mediating polar auxin transport is one of the important points of interaction with other hormones. Multiple hormonal pathways converge at the regulation of auxin transport and form a regulatory network that integrates various developmental and environmental inputs to steer plant development. In this review, we discuss recent advances in understanding the mechanisms that underlie regulation of polar auxin transport by multiple hormonal pathways. Specifically, we focus on the post-translational mechanisms that contribute to fine-tuning of the abundance and polarity of auxin transporters at the plasma membrane and thereby enable rapid modification of the auxin flow to coordinate plant growth and development.

Modeling of asymmetric division of somatic cell in protoplasts culture of higher plants

The key result of the work is the selection of factors for the cultivation of protoplasts of higher plants in vitro, which allowed induction of asymmetrical cell division during the first cell cycle phase. Gibberellin has been proved to be one of the main cofactors of asymmetric division of plant cells. The objects of research were plants of the following cultivars aseptically grown in hormone-free MS medium: tobacco (Nicotiana tabacum L.), SR-1 line; Arabidopsis thaliana var. columbia (L.) Heynh; potato (Solanum tuberosum L.), Zarevo cultivar; cultivated white head cabbage (Brassica oleraceae var. capitata L.) of the following varieties: Kharkivska zymnia, Ukrainska osin, Yaroslavna, Lika, Lesya, Bilosnizhka, Dithmarscher Früher, Iyunskarannya; rape (Brassica napus L.) of Shpat cultivar; winter radish (Raphanus sativus L.) of Odessa-5 cultivar. In experiments with mesophilic and hypocotyl protoplasts of the above-mentioned plant species it has been proved that short-term osmotic stress within 16–18 hours being combined with subsequent introduction of high doses of gibberellin GK3 (1 mg/L) into the modified liquid nutrient media TM and SW led to the occurrence of pronounced morphological traits of cytodifferentiation already at the initial stages of the development of mitotically active cells in a number of higher plants. Meanwhile, in all analyzed species, there was observed the division of the initial genetically homogeneous population of mitotically active cells into two types of asymmetric division: by the type of division of the mother cell into smaller daughter cells and by the type of the first asymmetric division of the zygotic embryo in planta. In this case, the first type of asymmetric division occurred during unusual cytomorphism of the mother cells: a pronounced heart-shaped form even before the first division, which is inherent in the morphology of somatic plant embryo in vitro at the heart-shaped stage. A particular study of the effect of osmotic stress influencing protoplasts of various cultivars of white cabbage, isolated from hypocotyls of 7–9 day etiolated seedlings, revealed quite a typical consistent pattern: the acquisition and maintenance of the axis of symmetry in growing microcolonies occurred without extra exogenous gibberellin (GK3), which was added to the nutrient medium earlier. While analyzing the effect of growth regulators on the formation of microcolonies with traits of structural organization, the conclusion was made regarding the commonality of the revealed morphogenetic reactions of cells within the culture of protoplasts of higher plants in vitro with similar reactions studied earlier on other plants, both in vitro and in planta. Modeling of asymmetric cell division in protoplast culture in vitro has become possible by carrying out a balanced selection of growth regulators as well as their coordinated application through time along with changes in osmotic pressure of a nutrient medium.

Gynoecium size and ovule number are interconnected traits that impact seed yield

Angiosperms form the largest group of land plants and display an astonishing diversity of floral structures. The development of flowers greatly contributed to the evolutionary success of the angiosperms as they guarantee efficient reproduction with the help of either biotic or abiotic vectors. The female reproductive part of the flower is the gynoecium (also called pistil). Ovules arise from meristematic tissue within the gynoecium. Upon fertilization, these ovules develop into seeds while the gynoecium turns into a fruit. Gene regulatory networks involving transcription factors and hormonal communication regulate ovule primordium initiation, spacing on the placenta, and development. Ovule number and gynoecium size are usually correlated and several genetic factors that impact these traits have been identified. Understanding and fine-tuning the gene regulatory networks influencing ovule number and pistil length open up strategies for crop yield improvement, which is pivotal in light of a rapidly growing world population. In this review, we present an overview of the current knowledge of the genes and hormones involved in determining ovule number and gynoecium size. We propose a model for the gene regulatory network that guides the developmental processes that determine seed yield.

Cryptochrome-mediated hypocotyl phototropism was regulated antagonistically by gibberellic acid and sucrose in Arabidopsis

Both phototropins (phot1 and phot2) and cryptochromes (cry1 and cry2) were proven as the Arabidopsis thaliana blue light receptors. Phototropins predominately function in photomovement, and cryptochromes play a role in photomorphogenesis. Although cryptochromes have been proposed to serve as positive modulators of phototropic responses, the underlying mechanism remains unknown. Here, we report that depleting sucrose from the medium or adding gibberellic acids (GAs) can partially restore the defects in phototropic curvature of the phot1 phot2 double mutants under high-intensity blue light; this restoration does not occur in phot1 phot2 cry1 cry2 quadruple mutants and nph3 (nonphototropic hypocotyl 3) mutants which were impaired phototropic response in sucrose-containing medium. These results indicate that GAs and sucrose antagonistically regulate hypocotyl phototropism in a cryptochromes dependent manner, but it showed a crosstalk with phototropin signaling on NPH3. Furthermore, cryptochromes activation by blue light inhibit GAs synthesis, thus stabilizing DELLAs to block hypocotyl growth, which result in the higher GAs content in the shade side than the lit side of hypocotyl to support the asymmetric growth of hypocotyl. Through modulation of the abundance of DELLAs by sucrose depletion or added GAs, it revealed that cryptochromes have a function in mediating phototropic curvature.

Rapid Detection of Hormonal Involvement in Light Responses

Many aspects of light-controlled metabolism and development of plants depend on hormonal pathways. Here, a method is described to identify such hormonal dependence in light-regulated processes. A number of compounds-hormones and chemicals which interfere with hormonal pathways-are listed because of their usefulness in pharmacological treatment experiments. As an example for practical use of such compounds, elongation growth is discussed. An experimental setup is described in which plants are grown so that their structures develop predominantly in a two-dimensional plane. Time-lapse imaging is used to follow the plants in time, and image analysis reveals changes in plant morphology.

Transcriptional and biochemical analyses of gibberellin expression and content in germinated barley grain

Mobilization of reserves in germinated cereal grains is critical for early seedling vigour, global crop productivity, and hence food security. Gibberellins (GAs) are central to this process. We have developed a spatio-temporal model that describes the multifaceted mechanisms of GA regulation in germinated barley grain. The model was generated using RNA sequencing transcript data from tissues dissected from intact, germinated grain, which closely match measurements of GA hormones and their metabolites in those tissues. The data show that successful grain germination is underpinned by high concentrations of GA precursors in ungerminated grain, the use of independent metabolic pathways for the synthesis of several bioactive GAs during germination, and a capacity to abort bioactive GA biosynthesis. The most abundant bioactive form is GA1, which is synthesized in the scutellum as a glycosyl conjugate that diffuses to the aleurone, where it stimulates de novo synthesis of a GA3 conjugate and GA4. Synthesis of bioactive GAs in the aleurone provides a mechanism that ensures the hormonal signal is relayed from the scutellum to the distal tip of the grain. The transcript data set of 33 421 genes used to define GA metabolism is available as a resource to analyse other physiological processes in germinated grain.

Plants make galls to accommodate foreigners: some are friends, most are foes

At the colonization site of a foreign entity, plant cells alter their trajectory of growth and development. The resulting structure - a plant gall - accommodates various needs of the foreigner, which are phylogenetically diverse: viruses, bacteria, protozoa, oomycetes, true fungi, parasitic plants, and many types of animals, including rotifers, nematodes, insects, and mites. The plant species that make galls also are diverse. We assume gall production costs the plant. All is well if the foreigner provides a gift that makes up for the cost. Nitrogen-fixing nodule-inducing bacteria provide nutritional services. Gall wasps pollinate fig trees. Unfortunately for plants, most galls are made for foes, some of which are deeply studied pathogens and pests: Agrobacterium tumefaciens, Rhodococcus fascians, Xanthomonas citri, Pseudomonas savastanoi, Pantoea agglomerans, 'Candidatus' phytoplasma, rust fungi, Ustilago smuts, root knot and cyst nematodes, and gall midges. Galls are an understudied phenomenon in plant developmental biology. We propose gall inception for discovering unifying features of the galls that plants make for friends and foes, talk about molecules that plants and gall-inducers use to get what they want from each other, raise the question of whether plants colonized by arbuscular mycorrhizal fungi respond in a gall-like manner, and present a research agenda.

Two SLENDER AND CRINKLY LEAF dioxygenases play an essential role in rice shoot development

It is clear that 2-oxoglutarate-dependent dioxygenases have critical functions in salicylic acid (SA) metabolism in plants, yet their role in SA biosynthesis is poorly understood. Here, we report that two dioxygenase-encoding genes, SLENDER AND CRINKLY LEAF1 (SLC1) and SLC2, play essential roles in shoot development and SA production in rice. Overexpression of SLC1 (SLC1-OE) or SLC2 (SLC2-OE) in rice produced infertile plants with slender and crinkly leaves. Disruption of SLC1 or SLC2 led to dwarf plants, while simultaneous down-regulation of SLC1 and SLC2 resulted in a severe defect in early leaf development. Enhanced SA levels in SLC1-OE plants and decreased SA levels in slc1 and slc2 mutants were observed. Accordingly, these lines all showed altered expression of a set of SA-related genes. We demonstrated that SLC1 interacts with homeobox1 (OSH1), and that either the knotted1-like homeobox (KNOX1) or glutamate, leucine, and lysine (ELK) domain of OSH1 is sufficient for accomplishing this interaction. Collectively, our data reveal the importance of SLC1 and SLC2 in rice shoot development.

The Ubiquitin-Binding Protein OsDSK2a Mediates Seedling Growth and Salt Responses by Regulating Gibberellin Metabolism in Rice

UBL-UBA (ubiquitin-like-ubiquitin-associated) proteins are ubiquitin receptors and transporters in the ubiquitin-proteasome system that play key roles in plant growth and development. High salinity restricts plant growth by disrupting cellular metabolism, but whether UBL-UBA proteins are involved in this process is unclear. Here, we demonstrate that the UBL-UBA protein OsDSK2a (DOMINANT SUPPRESSOR of KAR2) mediates seedling growth and salt responses in rice (Oryza sativa). Through analysis of osdsk2a, a mutant with retarded seedling growth, as well as in vitro and in vivo assays, we demonstrate that OsDSK2a combines with polyubiquitin chains and interacts with the gibberellin (GA)-deactivating enzyme ELONGATED UPPERMOST INTERNODE (EUI), resulting in its degradation through the ubiquitin-proteasome system. Bioactive GA levels were reduced, and plant growth was retarded in the osdsk2a mutant. By contrast, eui mutants displayed increased seedling growth and bioactive GA levels. OsDSK2a levels decreased in plants under salt stress. Moreover, EUI accumulated under salt stress more rapidly in osdsk2a than in wild-type plants. Thus, OsDSK2a and EUI play opposite roles in regulating plant growth under salt stress by affecting GA metabolism. Under salt stress, OsDSK2a levels decrease, thereby increasing EUI accumulation, which promotes GA metabolism and reduces plant growth.

Gibberellins and Heterosis in Crops and Trees: An Integrative Review and Preliminary Study with Brassica

Heterosis, or hybrid vigor, has contributed substantially to genetic improvements in crops and trees and its physiological basis involves multiple processes. Four associations with the phytohormone gibberellin (GA) indicate its involvement in the regulation of heterosis for shoot growth in maize, sorghum, wheat, rice, tomato and poplar. (1) Inbreds somewhat resemble GA-deficient dwarfs and are often highly responsive to exogenous GA₃. (2) Levels of endogenous GAs, including the bioeffector GA₁, its precursors GA₁₉ and GA₂₀, and/or its metabolite GA₈, are higher in some fast-growing hybrids than parental genotypes. (3) Oxidative metabolism of applied [³H]GAs is more rapid in vigorous hybrids than inbreds, and (4) heterotic hybrids have displayed increased expression of GA biosynthetic genes including GA 20-oxidase and GA 3-oxidase. We further investigated Brassicarapa, an oilseed rape, by comparing two inbreds (AO533 and AO539) and their F₁ hybrid. Seedling emergence was faster in the hybrid and potence ratios indicated dominance for increased leaf number, area and mass, and stem mass. Overdominance (heterosis) was displayed for root mass, leading to slight heterosis for total plant mass. Stem contents of GA_19,20,1 were similar across the Brassica genotypes and increased prior to bolting; elongation was correlated with endogenous GA but heterosis for shoot growth was modest. The collective studies support a physiological role for GAs in the regulation of heterosis for shoot growth in crops and trees, and the Brassica study encourages further investigation of heterosis for root growth.

Molecular Changes Concomitant with Vascular System Development in Mature Galls Induced by Root-Knot Nematodes in the Model Tree Host Populus tremula × P. alba

One of the most striking features occurring in the root-knot nematode Meloidogyne incognita induced galls is the reorganization of the vascular tissues. During the interaction of the model tree species Populus and M. incognita, a pronounced xylem proliferation was previously described in mature galls. To better characterise changes in expression of genes possibly involved in the induction and the formation of the de novo developed vascular tissues occurring in poplar galls, a comparative transcript profiling of 21-day-old galls versus uninfected root of poplar was performed. Genes coding for transcription factors associated with procambium maintenance and vascular differentiation were shown to be differentially regulated, together with genes partaking in phytohormones biosynthesis and signalling. Specific signatures of transcripts associated to primary cell wall biosynthesis and remodelling, as well as secondary cell wall formation (cellulose, xylan and lignin) were revealed in the galls. Ultimately, we show that molecules derived from the monolignol and salicylic acid pathways and related to secondary cell wall deposition accumulate in mature galls.

Crosstalk with Jasmonic Acid Integrates Multiple Responses in Plant Development

To date, extensive studies have identified many classes of hormones in plants and revealed the specific, nonredundant signaling pathways for each hormone. However, plant hormone functions largely overlap in many aspects of plant development and environmental responses, suggesting that studying the crosstalk among plant hormones is key to understanding hormonal responses in plants. The phytohormone jasmonic acid (JA) is deeply involved in the regulation of plant responses to biotic and abiotic stresses. In addition, a growing number of studies suggest that JA plays an essential role in the modulation of plant growth and development under stress conditions, and crosstalk between JA and other phytohormones involved in growth and development, such as gibberellic acid (GA), cytokinin, and auxin modulate various developmental processes. This review summarizes recent findings of JA crosstalk in the modulation of plant growth and development, focusing on JA–GA, JA–cytokinin, and JA–auxin crosstalk. The molecular mechanisms underlying this crosstalk are also discussed.

Gibberellin-regulated protein allergy: Clinical features and cross-reactivity

Gibberellin-regulated proteins (GRPs)/GASA proteins are members of cysteine-rich antimicrobial peptide families and are conserved in a broad range of plants. Some GRPs in fruits and pollens have been identified as allergens including peach Pru p 7, Japanese apricot Pru m 7, orange Cit s 7, pomegranate Pun g 7, and cypress pollen GRP. The clinical features of fruit-derived GRP allergies frequently include systemic reactions, multiple fruit allergies regardless of plant kingdom classifications and, less frequently, cofactor-dependence. Multiple fruit allergies might be related to cross-reactivity between GRPs. Clinical cross-reactivity, at least between the four fruit-derived GRPs, has been proven. In addition, GRP allergy induces peculiar clinical symptoms, such as laryngeal tightness and facial swelling, especially eyelid edema, which was proposed to be a predictive factor for Pru p 7 allergy. Fruit-derived GRPs have an unusually high content of cysteine, resulting in high stability to heat and resistance to digestive enzymes. Therefore, GRPs are considered "true" food allergens that induce severe allergic reactions. As an alternative mechanism of fruit-derived GRP allergies, cross-reactivity between fruit GRP and cypress pollen GRP, which might play a role as a sensitizer, is suspected. Taken together, these characteristics indicate GRPs are clinically relevant plant allergens. This review article summarizes our current knowledge of the clinical features and important aspects of GRP sensitization and allergy.

PbGA20ox2 Regulates Fruit Set and Induces Parthenocarpy by Enhancing GA4 Content

Fruit set and development occur following successful fertilization. Parthenocarpy, a valuable trait in some self-incompatible species, produces seedless fruit without fertilization. Gibberellin (GA) is a crucial hormone in fruit-set regulation and development. While investigating the development of parthenocarpy in pear (Pyrus bretschneideri Rehd.), we determined that GA 20-oxidases (GA20ox) may play key roles in seedless pear fruit development. Sequence analysis revealed three PbGA20ox genes: PbGA20ox1, PbGA20ox2, and PbGA20ox3. We analyzed the expression patterns of candidate genes and found that PbGA20ox2 levels significantly changed in pollinated fruits. Tissue-specific expression assays revealed that PbGA20ox2 is highly expressed in young fruit and leaves. Subcellular localization assays showed it was located in the cytoplasm, nucleus, and plasma membrane. Overexpressed PbGA20ox2 tomato plants were taller and had longer hypocotyls and internodes, and the emasculated flowers produced parthenocarpic fruit. In pear, the transient overexpression of PbGA20ox2 promoted fruit development and delayed the drop of nonpollinated fruit. Furthermore, the fruit of PbGA20ox2-overexpressing tomato and transient PbGA20ox2-overexpressing pear had increased GA₄ (but not GA₃ and GA₁) contents. This result provided evidence that PbGA20ox2 was necessary for GA₄-dependent pear fruit development. Our study revealed that PbGA20ox2 altered the GA biosynthetic pathway and enhanced GA₄ synthesis, thereby promoting fruit set and parthenocarpic fruit development.

Gibberellin Metabolism in Flowering Plants: An Update and Perspectives

In plants, gibberellins (GAs) play important roles in regulating growth and development. Early studies revealed the large chemodiversity of gibberellins in plants, but only GA₁, GA₃, GA₄, and GA₇ show biological activity that controls plant development. However, the elucidation of the GA metabolic network at the molecular level has lagged far behind the chemical discovery of GAs. Recent advances in downstream GA biosynthesis (after GA₁₂ formation) suggest that species-specific gibberellin modifications were acquired during flowering plant evolution. Here, we summarize the current knowledge of GA metabolism in flowering plants and the physiological functions of GA deactivation, with a focus on GA 13 hydroxylation. The potential applications of GA synthetic biology for plant development are also discussed.

Dual Role of Gibberellin in Perennial Shoot Branching: Inhibition and Activation

Shoot branching from axillary buds (AXBs) is regulated by a network of inhibitory and promotive forces, which includes hormones. In perennials, the dwarfed stature of the embryonic shoot inside AXBs is indicative of gibberellin (GA) deficiency, suggesting that AXB activation and outgrowth require GA. Nonetheless, the role of GA in branching has remained obscure. We here carried out comprehensive GA transcript and metabolite analyses in hybrid aspen, a perennial branching model. The results indicate that GA has an inhibitory as well as promotive role in branching. The latter is executed in two phases. While the expression level of GA2ox is high in quiescent AXBs, decapitation rapidly downregulated it, implying increased GA signaling. In the second phase, GA3ox2-mediated de novo GA-biosynthesis is initiated between 12 and 24 h, prior to AXB elongation. Metabolite analyzes showed that GA_1/4 levels were typically high in proliferating apices and low in the developmentally inactive, quiescent AXBs, whereas the reverse was true for GA_3/6. To investigate if AXBs are differently affected by GA₃, GA₄, and GR24, an analog of the branch-inhibitor hormone strigolactone, they were fed into AXBs of single-node cuttings. GA₃ and GA₄ had similar effects on GA and SL pathway genes, but crucially GA₃ induced AXB abscission whereas GA₄ promoted outgrowth. Both GA₃ and GA₄ strongly upregulated GA2ox genes, which deactivate GA_1/4 but not GA_3/6. Thus, the observed production of GA_3/6 in quiescent AXBs targets GA_1/4 for GA2ox-mediated deactivation. AXB quiescence can therefore be maintained by GA_3/6, in combination with strigolactone. Our discovery of the distinct tasks of GA₃ and GA₄ in AXB activation might explain why the role of GA in branching has been difficult to decipher. Together, the results support a novel paradigm in which GA_3/6 maintains high levels of GA2ox expression and low levels of GA₄ in quiescent AXBs, whereas activation and outgrowth require increased GA_1/4 signaling through the rapid reduction of GA deactivation and subsequent GA biosynthesis.

A strategy to reduce the dose of multichiral agricultural chemicals: The herbicidal activity of metolachlor against Echinochloa crusgalli

Agricultural chemicals are normally used as mixtures of several isomers, e.g., enantiomers. In theory, in order to minimize the pesticides dose, it is desirable to use the most target-active isomer. Metolachlor is a typical multichiral herbicide belonging to amide herbicides. An asymmetric carbon atom and a chiral axis yield four stereoisomers. In this study, a novel laboratory method was developed to prepare the S-metolachlor and the four stereoisomers using high performance liquid chromatography. The separated isomers had a purity of >99%, with their absolute configurations assigned by electronic circular dichroism. The enantioseparation by ultra performance convergence chromatography tandem mass spectrometry was also performed for the rapid and sensitive detection of metolachlor stereoisomers. The enantioselective herbicidal activity toward the target weed (Echinochloa crusgalli) was systematically assessed for the first time by measuring the morphology of the weed after treatment with rac-, S-metolachlor and the four stereoisomers, respectively. Among the commercial pesticides, S-metolachlor was more effective in weed inhibition than rac-metolachlor, and to the four stereoisomers, the herbicidal activities were ranked as: SS > SR ≫ RS > RR, and the RR-isomer even had some stimulative effect to the weed growth at lower concentration (1 ppm). Thus, we concluded that in these cases, the chiral carbon feature played a major role in herbicidal activity rather than the chiral axis feature, and the higher bioactivity of the S-isomers was confirmed by more effective uptake and stronger interaction with target enzymes that were involved in the gibberellic acid biosynthesis. Although the SS-isomer shows the highest herbicidal activity, controlling the major chiral feature is still much easier and more economical than controlling two chiral features.

Small Grain and Dwarf 2, encoding an HD-Zip II family transcription factor, regulates plant development by modulating gibberellin biosynthesis in rice

Homeodomain leucine zipper (HD-Zip) proteins are transcription factors that regulate plant development. Bioactive gibberellin (GA) is a key endogenous hormone that participates in plant growth. However, the relationship between HD-Zip genes and modulation of GA biosynthesis in rice remains elusive. Here, we identified a rice mutant, designated as small grain and dwarf 2 (sgd2), which had reduced height and grain size compared with the wild type. Cytological observations indicated that the defective phenotype was mainly due to decreased cell length. Map-based cloning and complementation tests demonstrated that a 9 bp deletion in a homeodomain leucine zipper (HD-Zip) II family transcription factor was responsible for the sgd2 mutant phenotype. Expression of SGD2 was pronounced in developing panicles, and its protein was localized in nucleus. Luciferase reporter system and transactivation assays in yeast suggested that SGD2 functioned as a transcriptional repressor. High performance liquid chromatography assays showed that the endogenous GA₁ level in the sgd2 mutant was dramatically decreased, and exogenous GA₃ recovered the second leaf sheath to normal length. Results of qRT-PCR showed that the expression levels of genes positively regulating GA-biosynthesis were mostly down-regulated in the mutant. Our data identified the role of an HD-Zip transcription factor that affects rice plant development by modulating gibberellin biosynthesis.

Multiple genes recruited from hormone pathways partition maize diterpenoid defences

Duplication and divergence of primary pathway genes underlie the evolution of plant specialized metabolism; however, mechanisms partitioning parallel hormone and defence pathways are often speculative. For example, the primary pathway intermediate ent-kaurene is essential for gibberellin biosynthesis and is also a proposed precursor for maize antibiotics. By integrating transcriptional coregulation patterns, genome-wide association studies, combinatorial enzyme assays, proteomics and targeted mutant analyses, we show that maize kauralexin biosynthesis proceeds via the positional isomer ent-isokaurene formed by a diterpene synthase pair recruited from gibberellin metabolism. The oxygenation and subsequent desaturation of ent-isokaurene by three promiscuous cytochrome P450s and a new steroid 5α reductase indirectly yields predominant ent-kaurene-associated antibiotics required for Fusarium stalk rot resistance. The divergence and differential expression of pathway branches derived from multiple duplicated hormone-metabolic genes minimizes dysregulation of primary metabolism via the circuitous biosynthesis of ent-kaurene-related antibiotics without the production of growth hormone precursors during defence.

Conserved bases for the initial cyclase in gibberellin biosynthesis: from bacteria to plants

All land plants contain at least one class II diterpene cyclase (DTC), which utilize an acid-base catalytic mechanism, for the requisite production of ent-copalyl diphosphate (ent-CPP) in gibberellin A (GA) phytohormone biosynthesis. These ent-CPP synthases (CPSs) are hypothesized to be derived from ancient bacterial origins and, in turn, to have given rise to the frequently observed additional DTCs utilized in more specialized plant metabolism. However, such gene duplication and neo-functionalization has occurred repeatedly, reducing the utility of phylogenetic analyses. Support for evolutionary scenarios can be found in more specific conservation of key enzymatic features. While DTCs generally utilize a DxDD motif as the catalytic acid, the identity of the catalytic base seems to vary depending, at least in part, on product outcome. The CPS from Arabidopsis thaliana has been found to utilize a histidine-asparagine dyad to ligate a water molecule that serves as the catalytic base, with alanine substitution leading to the production of 8β-hydroxy-ent-CPP. Here this dyad and effect of Ala substitution is shown to be specifically conserved in plant CPSs involved in GA biosynthesis, providing insight into plant DTC evolution and assisting functional assignment. Even more strikingly, while GA biosynthesis arose independently in plant-associated bacteria and fungi, the catalytic base dyad also is specifically found in the relevant bacterial, but not fungal, CPSs. This suggests functional conservation of CPSs from bacteria to plants, presumably reflecting an early role for derived diterpenoids in both plant development and plant-microbe interactions, eventually leading to GA, and a speculative evolutionary scenario is presented.

Revolutions in agriculture chart a course for targeted breeding of old and new crops

The dominance of the major crops that feed humans and their livestock arose from agricultural revolutions that increased productivity and adapted plants to large-scale farming practices. Two hormone systems that universally control flowering and plant architecture, florigen and gibberellin, were the source of multiple revolutions that modified reproductive transitions and proportional growth among plant parts. Although step changes based on serendipitous mutations in these hormone systems laid the foundation, genetic and agronomic tuning were required for broad agricultural benefits. We propose that generating targeted genetic variation in core components of both systems would elicit a wider range of phenotypic variation. Incorporating this enhanced diversity into breeding programs of conventional and underutilized crops could help to meet the future needs of the human diet and promote sustainable agriculture.

Influence of Preharvest Gibberellic Acid Treatments on Postharvest Quality of Minimally Processed Leaf Lettuce and Rocket

Plant growth regulators are used in high-value vegetable crops during cultivation and after harvest to increase yield, enhance crop management, and improve or retain the produce quality. The aim of this work was to evaluate the quality characteristics during cold storage of minimally processed leaf lettuce and rocket, obtained from plants grown in a hydroponic floating system with mineral nutrient solutions (MNS) containing different levels of gibberellic acid (GA3). Plants were grown in greenhouse conditions on nutrient solutions containing 0, 10−8, and 10−6 M GA3. At harvest, lettuce and rocket were immediately processed as fresh-cut vegetables and stored for 21 d at 4 °C. After processing, weight loss, total soluble solids, titratable acidity, ascorbic acid and nitrate content, leaf color characteristics, and overall quality were evaluated. Adding 10−6 M GA3 to the MNS of a floating system significantly increased the yield of leaf lettuce and rocket plants and of minimally-processed leaves. In addition, preharvest GA3 treatments had positive effects on delaying senescence and enhancing shelf-life of minimally processed lettuce and rocket. The slowed senescence of GA3-treated samples maintained an overall quality over the threshold of marketability in both lettuce and rocket for up to 21 d of cold storage.

OsGASR9 positively regulates grain size and yield in rice (Oryza sativa)

The plant-specific gibberellic acid (GA)-stimulated transcript gene family is critical for plant growth and development. There are 10 family members in rice (Oryza sativa), known as OsGASRs. However, few have been functionally characterized. Here, we investigated the function of OsGASR9 in rice. OsGASR9 transcripts were detected in various tissues, with the lowest and highest levels in leaves and panicles, respectively. Greater mRNA levels accumulated in young, compared with in old, panicles and spikelets. OsGASR9 localized to the plasma membrane, cytoplasm and nucleus. Transgenic RNA interference-derived lines in the Zhonghua 11 background exhibited reduced plant height, grain size and yield compared with the wild-type. The two osgasr9 mutants in the Nipponbare background showed similar phenotypes. Conversely, the overexpression of OsGASR9 in the two backgrounds increased plant height and grain size. A significantly increased grain yield per plant was also observed in the overexpression lines having a Nipponbare background. Furthermore, by measuring the GA-induced lengths of the second leaf sheaths and α-amylase activity levels of seeds, we concluded that OsGASR9 is a positive regulator of responses to GA in rice. Thus, OsGASR9 may regulate plant height, grain size and yield through the GA pathway and could have an application value in breeding.

One-pot sample preparation approach for profiling spatial distribution of gibberellins in a single shoot of germinating cereal seeds

Sample preparation remains a bottleneck in the rapid and reliable quantification of gibberellins (GAs) for obtaining an insight into the physiological processes mediated by GAs. The challenges arise from not only the extremely low content of GAs in complex plant matrices, but the poor detectability of GAs by mass spectrometry (MS) in negative ion mode. In an effort to solve these urgent difficulties, we present a spatial-resolved analysis method to investigate the distribution of GAs in tiny plant tissues based on a simplified one-pot sample preparation approach coupled with ultrahigh-performance liquid chromatography-tandem MS. By integrating extraction and derivatization into one step, target GAs were effectively extracted from plant materials and simultaneously reacted with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide, the sample preparation time was largely shortened, the probability of sample loss was minimized and the detection sensitivity of MS was also greatly improved compared with underivatized GAs. Under optimal conditions, the method was validated from the quantification linearity, limits of detection and limits of quantification in the presence of plant matrices, recoveries, and precision. With the proposed method, 15 endogenous GAs were detected and, among these, 11 GAs could be quantified in 0.50 mg fresh weight (FW) wheat shoot samples, and five GAs were quantified in only 0.15 mg FW developing seed samples of Arabidopsis thaliana. The distribution patterns of GAs along both the non-13-hydroxylation pathway and the early 13-hydroxylation pathway in a single shoot of germinating wheat, rice and maize seeds were finally profiled with a spatial resolution down to approximately 1 mm² .

Improving Lodging Resistance: Using Wheat and Rice as Classical Examples

One of the most chronic constraints to crop production is the grain yield reduction near the crop harvest stage by lodging worldwide. This is more prevalent in cereal crops, particularly in wheat and rice. Major factors associated with lodging involve morphological and anatomical traits along with the chemical composition of the stem. These traits have built up the remarkable relationship in wheat and rice genotypes either prone to lodging or displaying lodging resistance. In this review, we have made a comparison of our conceptual perceptions with foregoing published reports and proposed the fundamental controlling techniques that could be practiced to control the devastating effects of lodging stress. The management of lodging stress is, however, reliant on chemical, agronomical, and genetic factors that are reducing the risk of lodging threat in wheat and rice. But, still, there are many questions remain to be answered to elucidate the complex lodging phenomenon, so agronomists, breeders, physiologists, and molecular biologists require further investigation to address this challenging problem.

The regulatory landscape of a core maize domestication module controlling bud dormancy and growth repression

Many domesticated crop plants have been bred for increased apical dominance, displaying greatly reduced axillary branching compared to their wild ancestors. In maize, this was achieved through selection for a gain-of-function allele of the TCP transcription factor teosinte branched1 (tb1). The mechanism for how a dominant Tb1 allele increased apical dominance, is unknown. Through ChIP seq, RNA seq, hormone and sugar measurements on 1 mm axillary bud tissue, we identify the genetic pathways putatively regulated by TB1. These include pathways regulating phytohormones such as gibberellins, abscisic acid and jasmonic acid, but surprisingly, not auxin. In addition, metabolites involved in sugar sensing such as trehalose 6-phosphate were increased. This suggests that TB1 induces bud suppression through the production of inhibitory phytohormones and by reducing sugar levels and energy balance. Interestingly, TB1 also putatively targets several other domestication loci, including teosinte glume architecture1, prol1.1/grassy tillers1, as well as itself. This places tb1 on top of the domestication hierarchy, demonstrating its critical importance during the domestication of maize from teosinte.

The TB1 transcription factor was selected for the increased apical dominance of maize compared to its ancestor teosinte. A metabolic and genomic analysis of domesticated axillary buds suggest that TB1 achieved this by regulating phytohormone signaling, sugar metabolism and other domestication genes.

Comparative transcriptome analysis provides key insights into seedling development in switchgrass (Panicum virgatum L.)

BACKGROUND

Switchgrass (Panicum virgatum L.), a warm-season perennial C4 plant, can be used as a forage plant, a soil and water conservation plant, a windbreak plant, and as a good source of biofuels and alternative energy with low planting costs. However, switchgrass exhibits low rates of seedling development compared to other crops, which means it is typically out-competed by weeds. There is a large variation in seedling development rates among different plantlets in switchgrass, which limits its usefulness for large-scale cultivation. Little is currently known about the molecular reasons for slow seedling growth.

RESULTS

Characterization of the seedling development process via growth indices indicated a relatively stagnant growth stage in switchgrass. A total of 678 differentially expressed genes (DEGs) were identified from the comparison of transcriptomes from slowly developed (sd) and rapidly developed (rd) switchgrass seedlings. Gene ontology and pathway enrichment analysis showed that DEGs were enriched in diterpenoid biosynthesis, thiamine metabolism, and circadian rhythm. Transcription factor enrichment and expression analyses showed MYB-related, bHLH and NAC family genes were essential for seedling growth. The transcriptome results were consistent with those of quantitative real-time polymerase chain reaction. Then, the expression profiles of maize and switchgrass were compared during seedling leaf development. A total of 128 DEGs that play key roles in seedling growth were aligned to maize genes. Transcriptional information and physiological indices suggested that several genes involved in the circadian rhythm, thiamine metabolism, energy metabolism, gibberellic acid biosynthesis, and signal transduction played important roles in seedling development.

CONCLUSIONS

The seedling development process of switchgrass was characterized, and the molecular differences between slowly developed and rapidly developed seedlings were discussed. This study provides new insights into the reasons for slow seedling development in switchgrass and will be useful for the genetic improvement of switchgrass and other crops.

Microbial small molecules - weapons of plant subversion

Covering: up to 2018 Plants live in close association with a myriad of microbes that are generally harmless. However, the minority of microbes that are pathogens can severely impact crop quality and yield, thereby endangering food security. By contrast, beneficial microbes provide plants with important services, such as enhanced nutrient uptake and protection against pests and diseases. Like pathogens, beneficial microbes can modulate host immunity to efficiently colonize the nutrient-rich niches within and around the roots and aerial tissues of a plant, a phenomenon mirroring the establishment of commensal microbes in the human gut. Numerous ingenious mechanisms have been described by which pathogenic and beneficial microbes in the plant microbiome communicate with their host, including the delivery of immune-suppressive effector proteins and the production of phytohormones, toxins and other bioactive molecules. Plants signal to their associated microbes via exudation of photosynthetically fixed carbon sources, quorum-sensing mimicry molecules and selective secondary metabolites such as strigolactones and flavonoids. Molecular communication thus forms an integral part of the establishment of both beneficial and pathogenic plant-microbe relations. Here, we review the current knowledge on microbe-derived small molecules that can act as signalling compounds to stimulate plant growth and health by beneficial microbes on the one hand, but also as weapons for plant invasion by pathogens on the other. As an exemplary case, we used comparative genomics to assess the small molecule biosynthetic capabilities of the Pseudomonas genus; a genus rich in both plant pathogenic and beneficial microbes. We highlight the biosynthetic potential of individual microbial genomes and the population at large, providing evidence for the hypothesis that the distinction between detrimental and beneficial microbes is increasingly fading. Knowledge on the biosynthesis and molecular activity of microbial small molecules will aid in the development of successful biological agents boosting crop resiliency in a sustainable manner and could also provide scientific routes to pathogen inhibition or eradication.