Evidence that high activity of vacuolar invertase is required for cotton fiber and Arabidopsis root elongation through osmotic dependent and independent pathways, respectively

A mechanohydraulic model supports a role for plasmodesmata in cotton fiber elongation

Plant cell growth depends on turgor pressure, the cell hydrodynamic pressure, which drives expansion of the extracellular matrix (the cell wall). Turgor pressure regulation depends on several physical, chemical, and biological factors, including vacuolar invertases, which modulate osmotic pressure of the cell, aquaporins, which determine the permeability of the plasma membrane to water, cell wall remodeling factors, which determine cell wall extensibility (inverse of effective viscosity), and plasmodesmata, which are membrane-lined channels that allow free movement of water and solutes between cytoplasms of neighboring cells, like gap junctions in animals. Plasmodesmata permeability varies during plant development and experimental studies have correlated changes in the permeability of plasmodesmal channels to turgor pressure variations. Here, we study the role of plasmodesmal permeability in cotton fiber growth, a type of cell that increases in length by at least three orders of magnitude in a few weeks. We incorporated plasmodesma-dependent movement of water and solutes into a classical model of plant cell expansion. We performed a sensitivity analysis to changes in values of model parameters and found that plasmodesmal permeability is among the most important factors for building up turgor pressure and expanding cotton fibers. Moreover, we found that nonmonotonic behaviors of turgor pressure that have been reported previously in cotton fibers cannot be recovered without accounting for dynamic changes of the parameters used in the model. Altogether, our results suggest an important role for plasmodesmal permeability in the regulation of turgor pressure.

Structure and Expression Analysis of PtrSUS, PtrINV, PtrHXK, PtrPGM, and PtrUGP Gene Families in Populus trichocarpa Torr. and Gray

Exogenous nitrogen and carbon can affect plant cell walls, which are composed of structural carbon. Sucrose synthase (SUS), invertase (INV), hexokinase (HXK), phosphoglucomutase (PGM), and UDP-glucose pyrophosphorylase (UGP) are the key enzymes of sucrose metabolism involved in cell wall synthesis. To understand whether these genes are regulated by carbon and nitrogen to participate in structural carbon biosynthesis, we performed genome-wide identification, analyzed their expression patterns under different carbon and nitrogen treatments, and conducted preliminary functional verification. Different concentrations of nitrogen and carbon were applied to poplar (Populus trichocarpa Torr. and Gray), which caused changes in cellulose, lignin, and hemicellulose contents. In poplar, 6 SUSs, 20 INVs, 6 HXKs, 4 PGMs, and 2 UGPs were identified. Moreover, the physicochemical properties, collinearity, and tissue specificity were analyzed. The correlation analysis showed that the expression levels of PtrSUS3/5, PtrNINV1/2/3/5/12, PtrCWINV3, PtrVINV2, PtrHXK5/6, PtrPGM1/2, and PtrUGP1 were positively correlated with the cellulose content. Meanwhile, the knockout of PtrNINV12 significantly reduced the cellulose content. This study could lay the foundation for revealing the functions of SUSs, INVs, HXKs, PGMs, and UGPs, which affected structural carbon synthesis regulated by nitrogen and carbon, proving that PtrNINV12 is involved in cell wall synthesis.

A comprehensive overview of cotton genomics, biotechnology and molecular biological studies

Cotton is an irreplaceable economic crop currently domesticated in the human world for its extremely elongated fiber cells specialized in seed epidermis, which makes it of high research and application value. To date, numerous research on cotton has navigated various aspects, from multi-genome assembly, genome editing, mechanism of fiber development, metabolite biosynthesis, and analysis to genetic breeding. Genomic and 3D genomic studies reveal the origin of cotton species and the spatiotemporal asymmetric chromatin structure in fibers. Mature multiple genome editing systems, such as CRISPR/Cas9, Cas12 (Cpf1) and cytidine base editing (CBE), have been widely used in the study of candidate genes affecting fiber development. Based on this, the cotton fiber cell development network has been preliminarily drawn. Among them, the MYB-bHLH-WDR (MBW) transcription factor complex and IAA and BR signaling pathway regulate the initiation; various plant hormones, including ethylene, mediated regulatory network and membrane protein overlap fine-regulate elongation. Multistage transcription factors targeting CesA 4, 7, and 8 specifically dominate the whole process of secondary cell wall thickening. And fluorescently labeled cytoskeletal proteins can observe real-time dynamic changes in fiber development. Furthermore, research on the synthesis of cotton secondary metabolite gossypol, resistance to diseases and insect pests, plant architecture regulation, and seed oil utilization are all conducive to finding more high-quality breeding-related genes and subsequently facilitating the cultivation of better cotton varieties. This review summarizes the paramount research achievements in cotton molecular biology over the last few decades from the above aspects, thereby enabling us to conduct a status review on the current studies of cotton and provide strong theoretical support for the future direction.

Morphology, sucrose metabolism and gene network reveal the molecular mechanism of seed fiber development in poplar

Poplar is an important tree species for ecological protection, wood production, bioenergy and urban greening; it has been widely planted worldwide. However, the catkin fibers produced by female poplars can cause environmental pollution and safety hazards during spring. This study focused on Populus tomentosa, and revealed the sucrose metabolism regulatory mechanism of catkin fibers development from morphological, physiological and molecular aspects. Paraffin section suggested that poplar catkin fibers were not seed hairs and produced from the epidermal cells of funicle and placenta. Sucrose degradation via invertase and sucrose synthase played the dominant role during poplar catkin fibers development. The expression patterns revealed that sucrose metabolism-related genes played important roles during catkin fibers development. Y1H analysis indicated that there was a potential interaction between sucrose synthase 2 (PtoSUS2)/vacuolar invertase 3 (PtoVIN3) and trichome-regulating MYB transcription factors in poplar. Finally, the two key genes, PtoSUS2 and PtoVIN3, had roles in Arabidopsis trichome density, indicating that sucrose metabolism is important in poplar catkin fibers development. This study is not only helpful for clarifying the mechanism of sucrose regulation during trichome development in perennial woody plants, but also establishes a foundation to solve poplar catkin fibers pollution through genetic engineering methods.

Regulatory and functional divergence among members of Ibβfruct2, a sweet potato vacuolar invertase gene controlling starch and glucose content

Sweet potato [Ipomoea batatas (L.) Lam.] is an important food and industrial crop. Its storage root is rich in starch, which is present in the form of granules and represents the principal storage carbohydrate in plants. Starch content is an important trait of sweet potato controlling the quality and yield of industrial products. Vacuolar invertase encoding gene Ibβfruct2 was supposed to be a key regulator of starch content in sweet potato, but its function and regulation were unclear. In this study, three Ibβfruct2 gene members were detected. Their promoters displayed differences in sequence, activity, and cis-regulatory elements and might interact with different transcription factors, indicating that the three Ibβfruct2 family members are governed by different regulatory mechanisms at the transcription level. Among them, we found that only Ibβfruct2-1 show a high expression level and promoter activity, and encodes a protein with invertase activity, and the conserved domains and three conserved motifs NDPNG, RDP, and WEC are critical to this activity. Only two and six amino acid residue variations were detected in sequences of proteins encoded by Ibβfruct2-2 and Ibβfruct2-3, respectively, compared with Ibβfruct2-1; although not within key motifs, these variations affected protein structure and affinities for the catalytic substrate, resulting in functional deficiency and low activity. Heterologous expression of Ibβfruct2-1 in Arabidopsis decreased starch content but increased glucose content in leaves, indicating Ibβfruct2-1 was a negative regulator of starch content. These findings represent an important advance in understanding the regulatory and functional divergence among duplicated genes in sweet potato, and provide critical information for functional studies and utilization of these genes in genetic improvement.

Fine mapping and candidate gene analysis of qFL-A12-5: a fiber length-related QTL introgressed from Gossypium barbadense into Gossypium hirsutum

The fiber length-related qFL-A12-5 identified in CSSLs introgressed from Gossypium barbadense into Gossypium hirsutum was fine-mapped to an 18.8 kb region on chromosome A12, leading to the identification of the GhTPR gene as a potential regulator of cotton fiber length. Fiber length is a key determinant of fiber quality in cotton, and it is a key target of artificial selection for breeding and domestication. Although many fiber length-related quantitative trait loci have been identified, there are few reports on their fine mapping or candidate gene validation, thus hampering efforts to understand the mechanistic basis of cotton fiber development. Our previous study identified the qFL-A12-5 associated with superior fiber quality on chromosome A12 in the chromosome segment substitution line (CSSL) MBI7747 (BC₄F_3:5). A single segment substitution line (CSSL-106) screened from BC₆F₂ was backcrossed to construct a larger segregation population with its recurrent parent CCRI45, thus enabling the fine mapping of 2852 BC₇F₂ individuals using denser simple sequence repeat markers to narrow the qFL-A12-5 to an 18.8 kb region of the genome, in which six annotated genes were identified in Gossypium hirsutum. Quantitative real-time PCR and comparative analyses led to the identification of GH_A12G2192 (GhTPR) encoding a tetratricopeptide repeat-like superfamily protein as a promising candidate gene for qFL-A12-5. A comparative analysis of the protein-coding regions of GhTPR among Hai1, MBI7747, and CCRI45 revealed two non-synonymous mutations. The overexpression of GhTPR resulted in longer roots in Arabidopsis, suggesting that GhTPR may regulate cotton fiber development. These results provide a foundation for future efforts to improve cotton fiber length.

Estimating the combining ability and genetic parameters for growth habit, yield, and fiber quality traits in some Egyptian cotton crosses

It is crucial to understand how targeted traits in a hybrid breeding program are influenced by gene activity and combining ability. During the three growing seasons of 2015, 2016, and 2017, a field study was conducted with twelve cotton genotypes, comprised of four testers and eight lines. Thirty-two F1 crosses were produced in the 2015 breeding season using the line x tester mating design. The twelve genotypes and their thirty-two F1 crosses were then evaluated in 2016 and 2017. The results demonstrated highly significant differences among cotton genotypes for all the studied traits, showing a wide range of genetic diversity in the parent genotypes. Additionally, the line-x-tester interaction was highly significant for all traits, suggesting the impact of both additive and non-additive variations in gene expression. Furthermore, the thirty-two cotton crosses showed high seed cotton output, lint cotton yield, and fiber quality, such as fiber length values exceeding 31 mm and a fiber strength above 10 g/tex. Accordingly, selecting lines and testers with high GCA effects and crosses with high SCA effects would be an effective approach to improve the desired traits in cotton and develop new varieties with excellent yield and fiber quality.

Genome-wide identification, characterization and evolutionary dynamic of invertase gene family in apple, and revealing its roles in cold tolerance

Invertases are ubiquitous enzymes that catalyze the unalterable cleavage of sucrose into glucose and fructose, and are crucially involved in plant growth, development and stress response. In this study, a total of 17 putative invertase genes, including 3 cell wall invertases, 3 vacuolar invertases, and 11 neutral invertases were identified in apple genome. Subcellular localization of MdNINV7 and MdNINV11 indicated that both invertases were located in the cytoplasm. Comprehensive analyses of physicochemical properties, chromosomal localization, genomic characterization, and gene evolution of MdINV family were conducted. Gene duplication revealed that whole-genome or segmental duplication and random duplication might have been the major driving force for MdINVs expansion. Selection index values, ω, showed strong evidence of positive selection signatures among the INV clusters. Gene expression analysis indicated that MdNINV1/3/6/7 members are crucially involved in fruit development and sugar accumulation. Similarly, expression profiles of MdCWINV1, MdVINV1, and MdNINV1/2/7/11 suggested their potential roles in response to cold stress. Furthermore, overexpression of MdNINV11 in apple calli at least in part promoted the expression of MdCBF1-5 and H₂O₂ detoxification in response to cold. Overall, our results will be useful for understanding the functions of MdINVs in the regulation of apple fruit development and cold stress response.

Where whole-genome duplication is most beneficial: Adaptation of mangroves to a wide salinity range between land and sea

Whole-genome duplication (WGD) is believed to increase the chance of adaptation to a new environment. This conjecture may apply particularly well to new environments that are not only different but also more variable than ancestral habitats. One such prominent environment is the interface between land and sea, which has been invaded by woody plants, collectively referred as mangroves, multiple times. Here, we use two distantly related mangrove species (Avicennia marina and Rhizophora apiculata) to explore the effects of WGD on the adaptive process. We found that a high proportion of duplicated genes retained after WGD have acquired derived differential expression in response to salt gradient treatment. The WGD duplicates differentially expressed in at least one copy usually (>90%) diverge from their paralogues' expression profiles. Furthermore, both species evolved in parallel to have one paralogue expressed at a high level in both fresh water and hypersaline conditions but at a lower level at medium salinity. The pattern contrasts with the conventional view of monotone increase/decrease as salinity increases. Differentially expressed copies have thus probably acquired a new role in salinity tolerance. Our results indicate that the WGD duplicates may have evolved to function collaboratively in coping with different salinity levels, rather than specializing in the intermediate salinity optimal for mangrove plants. In conclusion, WGD and the retained duplicates appear to be an effective solution for adaptation to new and unstable environments.

Genetic Determinants of Fiber-Associated Traits in Flax Identified by Omics Data Integration

In this paper, we explore potential genetic factors in control of flax phenotypes associated with fiber by mining a collection of 306 flax accessions from the Federal Research Centre of the Bast Fiber Crops, Torzhok, Russia. In total, 11 traits were assessed in the course of 3 successive years. A genome-wide association study was performed for each phenotype independently using six different single-locus models implemented in the GAPIT3 R package. Moreover, we applied a multivariate linear mixed model implemented in the GEMMA package to account for trait correlations and potential pleiotropic effects of polymorphisms. The analyses revealed a number of genomic variants associated with different fiber traits, implying the complex and polygenic control. All stable variants demonstrate a statistically significant allelic effect across all 3 years of the experiment. We tested the validity of the predicted variants using gene expression data available for the flax fiber studies. The results shed new light on the processes and pathways associated with the complex fiber traits, while the pinpointed candidate genes may be further used for marker-assisted selection.

Functional characterization of a cell wall invertase inhibitor StInvInh1 revealed its involvement in potato microtuber size in vitro

Cell wall invertase (CWI) is as an essential coordinator in carbohydrate partitioning and sink strength determination, thereby playing key roles in plant development. Emerging evidence revealed that the subtle regulation of CWI activity considerably depends on the post-translational mechanism by their inhibitors (INHs). In our previous research, two putative INHs (StInvInh1 and StInvInh3) were expected as targets of CWI in potato (Solanum tubersum), a model species of tuberous plants. Here, transcript analysis revealed that StInvInh1 showed an overall higher expression than StInhInh3 in all tested organs. Then, StInvInh1 was further selected to study. In accordance with this, the activity of StInvInh1 promoter increased with the development of leaves in plantlets but decreased with the development of microtubers in vitro and mainly appeared in vascular bundle. The recombinant protein StInvInh1 displayed inhibitory activities on the extracted CWI in vitro and StInvInh1 interacted with a CWI StcwINV2 in vivo by bimolecular fluorescence complementation. Furthermore, silencing StInvInh1 in potato dramatically increased the CWI activity without changing activities of vacuolar and cytoplasmic invertase, indicating that StInvInh1 functions as a typical INH of CWI. Releasing CWI activity in StInvInh1 RNA interference transgenic potato led to improvements in potato microtuber size in coordination with higher accumulations of dry matter in vitro. Taken together, these findings demonstrate that StInvInh1 encodes an INH of CWI and regulates the microtuber development process through fine-tuning apoplastic sucrose metabolism, which may provide new insights into tuber development.

Integrated Transcriptome and Targeted Metabolite Analysis Reveal miRNA-mRNA Networks in Low-Light-Induced Lotus Flower Bud Abortion

Most Nelumbo nucifera (lotus) flower buds were aborted during the growing season, notably in low-light environments. How lotus produces so many aborted flower buds is largely unknown. An integrated transcriptome and targeted metabolite analysis was performed to reveal the genetic regulatory networks underlying lotus flower bud abortion. A total of 233 miRNAs and 25,351 genes were identified in lotus flower buds, including 68 novel miRNAs and 1108 novel genes. Further enrichment analysis indicated that sugar signaling plays a potential central role in regulating lotus flower bud abortion. Targeted metabolite analysis showed that trehalose levels declined the most in the aborting flower buds. A potential regulatory network centered on miR156 governs lotus flower bud abortion, involving multiple miRNA-mRNA pairs related to cell integrity, cell proliferation and expansion, and DNA repair. Genetic analysis showed that miRNA156-5p-overexpressing lotus showed aggravated flower bud abortion phenotypes. Trehalose-6-P synthase 1 (TPS1), which is required for trehalose synthase, had a negative regulatory effect on miR156 expression. TPS1-overexpression lotus showed significantly decreased flower bud abortion rates both in normal-light and low-light environments. Our study establishes a possible genetic basis for how lotus produces so many aborted flower buds, facilitating genetic improvement of lotus’ shade tolerance.

The Pivotal Role of Major Chromosomes of Sub-Genomes A and D in Fiber Quality Traits of Cotton

Lack of precise information about the candidate genes involved in a complex quantitative trait is a major obstacle in the cotton fiber quality improvement, and thus, overall genetic gain in conventional phenotypic selection is low. Recent molecular interventions and advancements in genome sequencing have led to the development of high-throughput molecular markers, quantitative trait locus (QTL) fine mapping, and single nucleotide polymorphisms (SNPs). These advanced tools have resolved the existing bottlenecks in trait-specific breeding. This review demonstrates the significance of chromosomes 3, 7, 9, 11, and 12 of sub-genomes A and D carrying candidate genes for fiber quality. However, chromosome 7 carrying SNPs for stable and potent QTLs related to fiber quality provides great insights for fiber quality-targeted research. This information can be validated by marker-assisted selection (MAS) and transgene in Arabidopsis and subsequently in cotton.

Glucose regulates cotton fiber elongation by interacting with brassinosteroid

In plants, glucose (Glc) plays important roles, as a nutrient and signal molecule, in the regulation of growth and development. However, the function of Glc in fiber development of upland cotton (Gossypium hirsutum) is unclear. Here, using gas chromatography-mass spectrometry (GC-MS), we found that the Glc content in fibers was higher than that in ovules during the fiber elongation stage. In vitro ovule culture revealed that lower Glc concentrations promoted cotton fiber elongation, while higher concentrations had inhibitory effects. The hexokinase inhibitor N-acetylglucosamine (NAG) inhibited cotton fiber elongation in the cultured ovules, indicating that Glc-mediated fiber elongation depends on the Glc signal transduced by hexokinase. RNA sequencing (RNA-seq) analysis and hormone content detection showed that 150mM Glc significantly activated brassinosteroid (BR) biosynthesis, and the expression of signaling-related genes was also increased, which promoted fiber elongation. In vitro ovule culture clarified that BR induced cotton fiber elongation in a dose-dependent manner. In hormone recovery experiments, only BR compensated for the inhibitory effects of NAG on fiber elongation in a Glc-containing medium. However, the ovules cultured with the BR biosynthetic inhibitor brassinazole and from the BR-deficient cotton mutant pag1 had greatly reduced fiber elongation at all the Glc concentrations tested. This demonstrates that Glc does not compensate for the inhibition of fiber elongation caused by BR biosynthetic defects, suggesting that the BR signaling pathway works downstream of Glc during cotton fiber elongation. Altogether, our study showed that Glc plays an important role in cotton fibre elongation, and crosstalk occurs between Glc and BR signaling during modulation of fiber elongation.

Identification and characterization of the AINV genes in five Gossypium species with potential functions of GhAINVs under abiotic stress

Acid invertase (AINV) is a kind of sucrose hydrolase with an important role in plants. Currently, the AINV genes have not been systematically studied in cotton. In this study, a total of 92 AINV genes were identified in five cotton species. The phylogenetic analysis revealed that the AINV proteins were divided into two subgroups in cotton: vacuolar invertase (VINV) and cell wall invertase (CWINV). The analysis of gene structures, conserved motifs, and three-dimensional protein structures suggested that GhAINVs were significantly conserved. The synteny analysis showed that whole-genome duplication was the main force promoting the expansion of the AINV gene family. The cis-element, transcriptome, and quantitative real time-polymerase chain reaction (qRT-PCR) showed that some GhAINVs were possibly associated with stress response. GhCWINV4, highly expressed in PEG treatment, was cloned, and subsequent virus-induced gene silencing assay confirmed that this gene was involved in the drought stress response. Overall, this study might be helpful for further analyzing the biological function of AINVs and provide clues for improving the resistance of cotton to stress.

Synergetic toxicity of silver nanoparticle and glyphosate on wheat (Triticum aestivum L.)

Silver nanoparticles (AgNPs) are one of the most commonly used nanomaterials in industrial and agricultural production. Glyphosate is a broad-spectrum systemic herbicide, which mainly acts in the phloem of weeds that compete with crop growth and is widely used in agriculture. This study investigated the interactive effects of AgNPs and glyphosate on the physiological morphology, gene transcription, and rhizosphere microorganisms of wheat. Our results demonstrated that wheat growth, and the structure and diversity of rhizosphere microorganisms were slightly influenced by AgNPs and glyphosate single treatment at the test concentration. However, AgNPs and glyphosate (Gly) combined treatment (AgNPs + Gly) strongly inhibited wheat growth and influenced gene transcription. In total, 955, 601, and 1336 genes were determined to be differentially expressed in AgNPs, glyphosate, and combined treatment, respectively. According to KEGG analysis, the combined groups induced an antioxidant response by upregulating the transcription of phenylpropanoid biosynthesis-related genes. In addition, more energy was needed, and disrupted cell membrane was shown in the combined treatment, which displayed in the upregulation of sucrose, starch, and lipid synthesis. Moreover, the relative abundance of Bradyrhizobium, Devosia, Kribbella, Sphingopyxis (nitrogen-fixing bacteria), and Streptomyces (plant growth-promoting bacteria) in soil microbiota were decreased, implicated that nitrogen fixation and some beneficial substance secretions were inhibited by the combined treatment. This study emphasized that the synergetic effects of AgNPs and glyphosate exerted a negative impact on wheat growth.

Ovary Abortion Induced by Combined Waterlogging and Shading Stress at the Flowering Stage Involves Amino Acids and Flavonoid Metabolism in Maize

Maize (Zea mays L.) crops on the North China Plain are often subject to continuous overcast rain at the flowering stage. This causes waterlogging and shading stresses simultaneously and leads to huge yield losses, but the causes of these yield losses remain largely unknown. To explore the factors contributing to yield loss caused by combined waterlogging and shading stress at the flowering stage, we performed phenotypic, physiological, and quasi-targeted metabolomics analyses of maize plants subjected to waterlogging, shading, and combined waterlogging and shading (WS) treatments. Analyses of phenotypic and physiological indexes showed that, compared with waterlogging or shading alone, WS resulted in lower source strength, more severe inhibition of ovary and silk growth at the ear tip, a reduced number of emerged silks, and a higher rate of ovary abortion. Changes in carbon content and enzyme activity could not explain the ovary abortion in our study. Metabolomic analyses showed that the events occurred in ovaries and silks were closely related to abortion, WS forced the ovary to allocate more resources to the synthesis of amino acids involved in the stress response, inhibited the energy metabolism, glutathione metabolism and methionine salvage pathway, and overaccumulation of H₂O₂. In silks, WS led to lower accumulation levels of specific flavonoid metabolites with antioxidant capacity, and to over accumulation of H₂O₂. Thus, compared with each single stress, WS more seriously disrupted the normal metabolic process, and resulted more serious oxidative stress in ovaries and silks. Amino acids involved in the stress response in ovaries and specific flavonoid metabolites with antioxidant capacity in silks play important roles during ovary abortion. These results identify novel traits for selection in breeding programs and targets for genome editing to increase maize yield under WS stress.

Functional Characterization of a Cucumber (Cucumis sativus L.) Vacuolar Invertase, CsVI1, Involved in Hexose Accumulation and Response to Low Temperature Stress

Cucumber (Cucumis sativus L.), an important vegetable plant species, is susceptible to low temperature stress especially during the seedling stage. Vacuolar invertase (VI) plays important roles in plant responses to abiotic stress. However, the molecular and biochemical mechanisms of VI function in cucumber, have not yet been completely understood and VI responses to low temperature stress and it functions in cold tolerance in cucumber seedlings are also in need of exploration. The present study found that hexose accumulation in the roots of cucumber seedlings under low temperature stress is closely related to the observed enhancement of invertase activity. Our genome-wide search for the vacuolar invertase (VI) genes in cucumber identified the candidate VI-encoding gene CsVI1. Expression profiling of CsVI1 showed that it was mainly expressed in the young roots of cucumber seedlings. In addition, transcriptional analysis indicated that CsVI1 expression could respond to low temperature stress. Recombinant CsVI1 proteins purified from Pichia pastoris and Nicotiana benthamiana leaves could hydrolyze sucrose into hexoses. Further, overexpression of CsVI1 in cucumber plants could increase their hexose contents and improve their low temperature tolerance. Lastly, a putative cucumber invertase inhibitor was found could form a complex with CsVI1. In summary, these results confirmed that CsVI1 functions as an acid invertase involved in hexose accumulation and responds to low temperature stress in cucumber seedlings.

Sucrose Metabolism and Transport in Grapevines, with Emphasis on Berries and Leaves, and Insights Gained from a Cross-Species Comparison

In grapevines, as in other plants, sucrose and its constituents glucose and fructose are fundamentally important and carry out a multitude of roles. The aims of this review are three-fold. First, to provide a summary of the metabolism and transport of sucrose in grapevines, together with new insights and interpretations. Second, to stress the importance of considering the compartmentation of metabolism. Third, to outline the key role of acid invertase in osmoregulation associated with sucrose metabolism and transport in plants.

Advances about the Roles of Membranes in Cotton Fiber Development

Cotton fiber is an extremely elongated single cell derived from the ovule epidermis and is an ideal model for studying cell development. The plasma membrane is tremendously expanded and accompanied by the coordination of various physiological and biochemical activities on the membrane, one of the three major systems of a eukaryotic cell. This review compiles the recent progress and advances for the roles of the membrane in cotton fiber development: the functions of membrane lipids, especially the fatty acids, sphingolipids, and phytosterols; membrane channels, including aquaporins, the ATP-binding cassette (ABC) transporters, vacuolar invertase, and plasmodesmata; and the regulation mechanism of membrane proteins, such as membrane binding enzymes, annexins, and receptor-like kinases.

Differential transcription pathways associated with rootstock-induced dwarfing in breadfruit (Artocarpus altilis) scions

BACKGROUND

Breadfruit (Artocarpus altilis) is a traditional staple tree crop throughout the tropics. Through interspecific grafting, a dwarf phenotype with over 50% reduction in plant height was identified when marang (Artocarpus odoratissimus) rootstocks were used. However, the molecular mechanism underlying the rootstock-induced breadfruit dwarfing is poorly understood.

RESULTS

An RNA-sequencing study of breadfruit scions at 22 months after grafting identified 5409 differentially expressed genes (DEGs) of which 2069 were upregulated and 3339 were downregulated in scion stems on marang rootstocks compared to those on self-graft. The DEGs were predominantly enriched for biological processes involved in carbon metabolism, cell wall organization, plant hormone signal transduction and redox homeostasis. The down-regulation of genes encoding vacuolar acid invertases and alkaline/neutral invertases, was consistent with the decreased activity of both enzymes, accompanying with a higher sucrose but lower glucose and fructose levels in the tissues. Key genes of biosynthetic pathways for amino acids, lipids and cell wall were down regulated, reflecting reduction of sucrose utilisation for stem growth on dwarfing rootstocks. Genes encoding sugar transporters, amino acid transporters, choline transporters, along with large number of potassium channels and aquaporin family members were down-regulated in scion stems on marang rootstocks. Lower activity of plasma membrane H⁺-ATPase, together with the predominance of genes encoding expansins, wall-associated receptor kinases and key enzymes for biosynthesis and re-modelling of cellulose, xyloglucans and pectins in down-regulated DGEs suggested impairment of cell expansion. Signalling pathways of auxin and gibberellin, along with strigolacton and brassinosteroid biosynthetic genes dominated the down-regulated DEGs. Phenylpropanoid pathway was enriched, with key lignin biosynthetic genes down-regulated, and flavonoid biosynthetic genes upregulated in scions on marang rootstocks. Signalling pathways of salicylic acid, jasmonic acid, ethylene and MAPK cascade were significantly enriched in the upregulated DEGs.

CONCLUSIONS

Rootstock-induced disruption in pathways regulating nutrient transport, sucrose utilisation, cell wall biosynthesis and networks of hormone transduction are proposed to impair cell expansion and stem elongation, leading to dwarf phenotype in breadfruit scions. The information provides opportunity to develop screening strategy for rootstock breeding and selection for breadfruit dwarfing.

Change of soluble acid invertase gene (SAI-1) haplotype in hybrid sorghum breeding program in China

Sugar metabolism is the most important and core one which drives plant growth and development. Invertases are key enzymes that regulate sugar metabolism. A still-growing number of studies have revealed that invertases play a crucial role in various aspects of plant growth and development. Crop yield is the product of sugar metabolism; it could be deduced that invertase also regulated the yield formation. So we have done a series of research on soluble acid invertase in sweet sorghum from enzyme activity to gene cloning and functional marker development. In this paper, we sequenced full length of SAI-1 gene in 69 grain sorghum parent lines, trying to see how it differs in their gene sequences and their distribution in related hybrid varieties released in the past. To our surprise, the result showed that B-lines and restore lines (R-line) have almost different SAI-1 haplotype distribution. The change of haplotype of SAI-1 gene is associated with yield gain as with grain sorghum breeding progress, which proved that SAI-1 may take a very important role in yield formation. And we also found the SAI-1 gene tends to become shorter as with the breeding advance, which means short sequence in introns, while exon remains unchanged leading to higher gene efficiency. The best SAI-1 haplotype combination of sorghum hybrid was also found for different planting regions. These findings are of great significance for improving breeding efficiency, understanding heterosis, and germplasm enhancement.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01231-2.

Looking into 'hair tonics' for cotton fiber initiation

Cotton fiber is the most important source of cellulose for the global textile industry. These hair-like single-celled trichomes develop from ovule epidermis. They are classified into long spinnable lint and short fuzz. A key objective in the cotton industry is to breed elite cultivars with fuzzless seeds carrying high lint yield. Molecular basis underlying lint and fuzz initiation remains obscure. Recent studies indicate fiber initiation is under the control of MYB-bHLH-WDR (MBW) transcription factor complex. Based on molecular genetic studies and gene expression patterns linking fiber phenotypes, we propose that specific but different sets of MBW genes are required to precisely regulate the initiation of the lint and fuzz fibers. Emerging evidence further points to sugar signaling as a 'hair-tonic' to boost fiber initiation through interaction with MBW complex and auxin signaling. An integrative model is provided as a conceptual framework for future studies to dissect the molecular network responsible for cotton fiber initiation.

GhN/AINV13 positively regulates cotton stress tolerance by interacting with the 14-3-3 protein

Neutral/alkaline invertases (N/AINVs) are sucrose hydrolases with important roles in plants. In this study, 15, 15, 15, 29, and 30 N/AINVs were identified in the Gossypium species, G. raimondii, G. herbaceum, G. arboreum, G. hirsutum, and G. barbadense, respectively. Along with two previously discovered branches, α and β, a new clade γ was first discovered in our study. Investigation of gene collinearity showed that whole-genome duplication (WGD) and polyploidization were responsible for the expansion of the N/AINV gene family in allopolyploid Gossypium. Moreover, expression patterns revealed that GhN/AINV3/13/17/23/24/28 from the β clade is highly expressed during the period of fiber initiation. The invertase activity of GhN/AINV13 and GhN/AINV23 were confirmed by restoring defects of invertase-deficient yeast mutant SEY2102. Treatments of abiotic stress showed that most GhN/AINVs were induced in response to polyethylene glycol (PEG) or salt stress. A virus-induced gene-silencing (VIGS) experiment and yeast two-hybrid assay demonstrated that GhN/AINV13 may interact with their positive regulators Gh14-3-3 proteins and participate in the fiber initiation or stress tolerance of cotton. Our results provided fundamental information regarding N/AINVs and highlight their potential functions in cotton stress tolerance.

PpINH1, an invertase inhibitor, interacts with vacuolar invertase PpVIN2 in regulating the chilling tolerance of peach fruit

Sucrose metabolism, particularly the decomposition of sucrose by invertase, plays a central role in plant responses to cold stress. Invertase inhibitors (INHs) evolved in higher plants as essential regulators of sucrose metabolism. By limiting invertase activity, INHs keep cellular sugar levels elevated, which provides enhanced protection to plants under stress. Our results showed that the expression of PpVIN2, the only vacuolar invertase (VIN) gene in peach fruit sensitive to chilling temperatures, increases significantly during cold storage, while VIN enzyme activity increases more modestly. We also found that peach fruit transiently overexpressing PpINH1 had decreased VIN activity. Interactions of PpINH1 and PpVIN2 with recombinant proteins were shown by yeast two-hybrid assays and bimolecular fluorescence complementation assays, as well as in vitro. During cold storage, trehalose-treated peach fruit had significantly increased PpINH1 expression, decreased VIN enzyme activity, and significantly higher sucrose content than did untreated fruit. As a result, the treated fruit had enhanced resistance to chilling injury. Collectively, our data show that the post-translational repression of VIN enzyme activity by PpINH1 helps maintain sucrose levels in peach fruit during cold storage, thereby improving resistance to chilling injury.

The peptidyl-prolyl isomerases FKBP15-1 and FKBP15-2 negatively affect lateral root development by repressing the vacuolar invertase VIN2 in Arabidopsis

The peptidyl-prolyl isomerases FKBP15-1 and FKBP15-2 negatively modulate lateral root development by repressing vacuolar invertase VIN2 activity. Lateral root (LR) architecture greatly affects the efficiency of nutrient absorption and the anchorage of plants. Although the internal phytohormone regulatory mechanisms that control LR development are well known, how external nutrients influence lateral root development remains elusive. Here, we characterized the function of two FK506-binding proteins, namely, FKBP15-1 and FKBP15-2, in Arabidopsis. FKBP15-1/15-2 genes were expressed prominently in the vascular bundles of the root basal meristem region, and the FKBP15-1/15-2 proteins were localized to the endoplasmic reticulum of the cells. Using IP-MS, Co-IP, and BiFC assays, we demonstrated that FKBP15-1 and FKBP15-2 interacted with vacuolar invertase 2 (VIN2). Compared to Col-0 and the single mutants, the fkbp15-1fkbp15-2 double mutant had more LRs, and presented higher sucrose catalytic activity. Moreover, genetic analysis showed genetic epistasis of VIN2 over FKBP15-1/FKBP15-2 in controlling LR development. Our results indicate that FKBP15-1 and FKBP15-2 participate in the control of LR number by inhibiting the catalytic activity of VIN2. Owing to the conserved peptidylprolyl cis-trans isomerase activity of FKBP family proteins, our results provide a clue for further analysis of the interplay between lateral root development and protein modification by FKBPs.

Activities of leaf and spike carbohydrate-metabolic and antioxidant enzymes are linked with yield performance in three spring wheat genotypes grown under well-watered and drought conditions

BACKGROUND

To improve our understanding about the physiological mechanism of grain yield reduction at anthesis, three spring wheat genotypes [L₁ (advanced line), L₂ (Vorobey) and L₃ (Punjab-11)] having contrasting yield potential under drought in field were investigated under controlled greenhouse conditions, drought stress was imposed at anthesis stage by withholding irrigation until all plant available water was depleted, while well-watered control plants were kept at 95% pot water holding capacity.

RESULTS

Compared to genotype L₁ and L₂, pronounced decrease in grain number (NGS), grain yield (GY) and harvest index (HI) were found in genotype L₃, mainly due to its greater kernel abortion (KA) under drought. A significant positive correlation of leaf monodehydroascorbate reductase (MDHAR) with both NGS and HI was observed. In contrast, significant negative correlations of glutathione S-transferase (GST) and vacuolar invertase (vacInv) both within source and sink were found with NGS and HI. Likewise, a significant negative correlation of leaf abscisic acid (ABA) with NGS was noticed. Moreover, leaf aldolase and cell wall peroxidase (cwPOX) activities were significantly and positively associated with thousand kernel weight (TKW).

CONCLUSION

Distinct physiological markers correlating with yield traits and higher activity of leaf aldolase and cwPOX may be chosen as predictive biomarkers for higher TKW. Also, higher activity of MDHAR within the leaf can be selected as a predictive biomarker for higher NGS in wheat under drought. Whereas, lower activity of vacInv and GST both within leaf and spike can be selected as biomarkers for higher NGS and HI. The results highlighted the role of antioxidant and carbohydrate-metabolic enzymes in the modulation of source-sink balance in wheat crops, which could be used as bio-signatures for breeding and selection of drought-resilient wheat genotypes for a future drier climate.

The acid invertase gene family is involved in internode elongation in Phyllostachys heterocycla cv. pubescens

Acid invertases (INVs) play a pivotal role in both vegetative and reproductive growth of plants. However, their possible functions in fast-growing plants such as bamboo are largely unknown. Here, we report the molecular characterization of acid INVs in Phyllostachys heterocycla cv. pubescens, a fast-growing bamboo species commercially grown worldwide. Nine acid INVs (PhINVs), including seven cell wall INVs (PhCWINV1, PhCWINV2, PhCWINV3, PhCWINV4, PhCWINV5, PhCWINV6 and PhCWINV7) and two vacuolar INVs (PhVINV11 and PhVINV12) were isolated. Bioinformatic analyses demonstrated that they all share high amino acid identity with other INVs from different plant species and contain the motifs typically conserved in acid INV. Enzyme activity assays revealed a significantly higher INV activity in the fast-growing tissues, such as the elongating internodes of stems. Detailed quantitative reverse-transcription PCR analyses showed various expression patterns of PhINVs at different developmental stages of the elongating stems. With the exception of PhCWINV6, all PhINVs were ubiquitously expressed in a developmental-specific manner. Further studies in Arabidopsis exhibited that constitutive expression of PhCWINV1, PhCWINV4 or PhCWINV7 increased the biomass production of transgenic plants, as indicated by augmented plant heights and shoot dry weights than the wild-type plants. All these results suggest that acid INVs play a crucial role in the internode elongation of P. heterocycla cv. pubescens and would provide valuable information for the dissection of their exact biological functions in the fast growth of bamboo.

Early-stage sugar beet taproot development is characterized by three distinct physiological phases

Despite the agronomic importance of sugar beet (Beta vulgaris L.), the early-stage development of its taproot has only been poorly investigated. Thus, the mechanisms that determine growth and sugar accumulation in sugar beet are largely unknown. In the presented study, a physiological characterization of early-stage sugar beet taproot development was conducted. Activities were analyzed for fourteen key enzymes of carbohydrate metabolism in developing taproots over the first 80 days after sowing. In addition, we performed in situ localizations of selected carbohydrate-metabolic enzyme activities, anatomical investigations, and quantifications of soluble carbohydrates, hexose phosphates, and phytohormones. Based on the accumulation dynamics of biomass and sucrose, as well as on anatomical parameters, the early phase of taproot development could be subdivided into three stages-prestorage, transition, secondary growth and sucrose accumulation stage-each of which was characterized by distinct metabolic and phytohormonal signatures. The enzyme activity signatures corresponding to these stages were also shown to be robustly reproducible in experiments conducted in two additional locations. The results from this physiological phenotyping approach contribute to the identification of the key regulators of sugar beet taproot development and open up new perspectives for sugar beet crop improvement concerning both physiological marker-based breeding and biotechnological approaches.

Nutritional component analyses of kiwifruit in different development stages by metabolomic and transcriptomic approaches

BACKGROUND

Metabolites in kiwifruit greatly influence nutritional values; however, the dynamic changes in nutrient composition and the gene expression level of yellow kiwifruit have not been studied so far. To investigate the types and accumulation patterns of metabolites, a metabolomics approach utilizing liquid chromatography-electrospray ionization mass spectrometry and transcriptomics were used to analyze the yellow flesh of kiwifruit cultivar 'jinshi 1' collected at different stages of days after full bloom.

RESULTS

In total, 285 metabolites were identified over the kiwifruit developmental stages. The composition of the metabolites of kiwifruit at different stages of development was different. The organic acids contents and their derivatives were higher at the initial stage of development and then gradually decreased. The lipids and amino acids contents fluctuated at different stages of development but did not change significantly. Transcript profiles throughout yellow kiwifruit development were constructed and analyzed, with a focus on the biosynthesis and metabolism of compounds such as sugars, organic acids and ascorbic acid, which are indispensable for the development and formation of quality fruit. The transcript levels of genes involved in sucrose and starch metabolism were consistent with the change in soluble sugar and starch content throughout kiwifruit development. The metabolism of ascorbic acid was primarily through the l-galactose pathway.

CONCLUSION

Our metabolome and transcriptome approach identified dynamic changes in five types of nutrient metabolite levels, and correlations among such levels, in developing fruit. The results provide information that can be used by metabolic engineers and molecular breeders to improve kiwifruit quality. © 2020 Society of Chemical Industry.

OsINV3 and Its Homolog, OsINV2, Control Grain Size in Rice

Vacuolar invertase is involved in sugar metabolism and plays a crucial role in plant growth and development, thus regulating seed size. However, information linking vacuolar invertase and seed size in rice is limited. Here we characterized a small grain mutant sg2 (grain size on chromosome 2) that showed a reduced in grain size and 1000-grain weight compared to the wild type. Map-based cloning and genetic complementation showed that OsINV3 is responsible for the observed phenotype. Loss-of-function of OsINV3 resulted in grains of smaller size when compared to the wild type, while overexpression showed increased grain size. We also obtained a T-DNA insertion mutant of OsINV2, which is a homolog of OsINV3 and generated double knockout (KO) mutants of OsINV2 and OsINV3 using CRISPR/Cas9. Genetic data showed that OsINV2, that has no effect on grain size by itself, reduces grain length and width in the absence of OsINV3. Altered sugar content with increased sucrose and decreased hexose levels, as well as changes vacuolar invertase activities and starch constitution in INV3^KO, INV2^KO, INV3^KOINV2^KO mutants indicate that OsINV2 and OsINV3 affect sucrose metabolism in sink organs. In summary, we identified OsINV3 as a positive regulator of grain size in rice, and while OsINV2 has no function on grain size by itself. In the absence of OsINV3, it is possible to detect a role of OsINV2 in the regulation of grain size. Both OsINV3 and OsINV2 are involved in sucrose metabolism, and thus regulate grain size. Our findings increase our understanding of the role of OsINV3 and its homolog, OsINV2, in grain size development and also suggest a potential strategy to improve grain yield in rice.

Overexpression of Sucrose Phosphate Synthase Enhanced Sucrose Content and Biomass Production in Transgenic Sugarcane

Sucrose phosphate synthase (SPS) is a key enzyme in sucrose synthesis, which controls sucrose content in plants. This study was designed to examine the efficacy of the overexpression of SoSPS1 gene on sucrose accumulation and carbon partitioning in transgenic sugarcane. The overexpression of SoSPS1 gene increased SPS activity and sucrose content in transgenic sugarcane leaves. More importantly, the overexpression enhanced soluble acid invertase (SAI) activity concomitant with the increase of glucose and fructose levels in the leaves, whereas sucrose synthase activity exhibited almost no change. In the stalk, a similar correlation was observed, but a higher correlation was noted between SPS activity and sugar content. These results suggest that SPS overexpression has both direct and indirect effects on sugar concentration and SAI activity in sugarcane. In addition, SPS overexpression resulted in a significant increase in plant height and stalk number in some transgenic lines compared to those in non-transgenic control. Taken together, these results strongly suggest that enhancing SPS activity is a useful strategy for improving sugarcane yield.

Interplay between turgor pressure and plasmodesmata during plant development

Plasmodesmata traverse cell walls, generating connections between neighboring cells. They allow intercellular movement of molecules such as transcription factors, hormones, and sugars, and thus create a symplasmic continuity within a tissue. One important factor that determines plasmodesmal permeability is their aperture, which is regulated during developmental and physiological processes. Regulation of aperture has been shown to affect developmental events such as vascular differentiation in the root, initiation of lateral roots, or transition to flowering. Extensive research has unraveled molecular factors involved in the regulation of plasmodesmal permeability. Nevertheless, many plant developmental processes appear to involve feedbacks mediated by mechanical forces, raising the question of whether mechanical forces and plasmodesmal permeability affect each other. Here, we review experimental data on how one of these forces, turgor pressure, and plasmodesmal permeability may mutually influence each other during plant development, and we discuss the questions raised by these data. Addressing such questions will improve our knowledge of how cellular patterns emerge during development, shedding light on the evolution of complex multicellular plants.

Systematic Analysis of Alkaline/Neutral Invertase Genes Reveals the Involvement of Smi-miR399 in Regulation of SmNINV3 and SmNINV4 in Salvia miltiorrhiza

Alkaline/neutral invertases (NINVs), which irreversibly catalyze the hydrolysis of sucrose into fructose and glucose, play crucial roles in carbohydrate metabolism and plant development. Comprehensive insights into NINV genes are lacking in Salvia miltiorrhiza, a well-known traditional Chinese medicinal (TCM) plant with significant medicinal and economic value. Through genome-wide prediction, nine putative SmNINV genes, termed SmNINV1-SmNINV9, were identified. Integrated analysis of gene structures, sequence features, conserved domains, conserved motifs and phylogenetic trees revealed the conservation and divergence of SmNINVs. The identified SmNINVs were differentially expressed in roots, stems, leaves, flowers, and different root tissues. They also responded to drought, salicylic acid, yeast extract, and methyl jasmonate treatments. More importantly, computational prediction and experimental validation showed that SmNINV3 and SmNINV4 were targets of Smi-miR399, a conserved miRNA previously shown to affect Pi uptake and translocation through the cleavage of PHOSPHATE2 (PHO2). Consistently, analysis of 43 NINV genes and 26 miR399 sequences from Arabidopsis thaliana, Populus trichocarpa, Manihot esculenta, and Solanum lycopersicum showed that various AtNINV, PtNINV, MeNINV, and SlNINV genes were regulated by miR399. It indicates that the miR399-NINV module exists widely in plants. Furthermore, Smi-miR399 also cleaved SmPHO2 transcripts in S. miltiorrhiza, suggesting the complexity of NINVs, PHO2, and miR399 networks.

OsVIN2 encodes a vacuolar acid invertase that affects grain size by altering sugar metabolism in rice

OsVIN2, a vacuolar invertase, affects grain size and yield by altering sugar composition, transport, and starch accumulation in rice. Grain size, a major determinant of rice yield, is influenced by many developmental and environmental factors. Sugar metabolism plays vital roles in plant development. However, the way in which sugar metabolism affects rice grain size remains largely elusive. In this study, we characterized the small grain-size rice mutant sgs1. Histological analyses showed that reduced spikelet hull and endosperm size results from decreased cell size rather than cell number. Map-based cloning and complementation tests revealed that a DaiZ7 transposon insertion in a vacuolar invertase gene OsVIN2 is responsible for the mutant phenotype. Subcellular distribution and biochemical analysis indicated that OsVIN2 is located in the vacuolar lumen, and that its sucrose hydrolysis activity is maintained under acidic conditions. Furthermore, an altered sugar content with increased sucrose and decreased hexose levels, as well as changes in invertase and sucrose synthase activities, sugar transport gene expression, and starch constitution in sgs1 implies that OsVIN2 affects sucrose metabolism, including sugar composition, transport, and conversion from the source to the sink organs. Collectively, OsVIN2 is involved in sugar metabolism, and thus regulates grain size; our findings provide insights into grain development and also suggest a potential strategy to improve grain quality and yield in rice.

Transcriptome analysis reveals differences in the mechanisms of fiber initiation and elongation between long- and short-fiber cotton (Gossypium hirsutum L.) lines

Background

Improving the yield and fiber quality of upland cotton is a goal of plant breeders. However, increasing the yield and quality of cotton fibers is becoming more urgent. While the growing human population needs more cotton fiber, climate change is reducing the amount of land on which cotton can be planted, or making it difficult to ensure that water and other resources will be available in optimal quantities. The most logical means of improving yield and quality is understanding and manipulating the genes involved. Here, we used comparative transcriptomics to explore differences in gene expression between long- and short-fiber cotton lines to identify candidate genes useful for cotton improvement.

Results

Light and electron microscopy revealed that the initial fiber density was significantly greater in our short-fiber group (SFG) than in our long-fiber group (LFG). Compared with the SFG fibers, the LFG fibers were longer at all developmental stages. Comparison of the LFG and SFG transcriptomes revealed a total of 3538 differentially expressed genes (DEGs). Notably, at all three developmental stages examined, two expression patterns, consistently downregulated (profile 0) and consistently upregulated (profile 7), were identified, and both were significantly enriched in the SFG and LFG. Twenty-two DEGs known to be involved in fiber initiation were detected in profile 0, while 31 DEGs involved in fiber elongation were detected in profile 7. Functional annotation suggested that these DEGs, which included ERF1, TUA2, TUB1, and PER64, affect fiber elongation by participating in the ethylene response, microtubule synthesis, and/or the peroxidase (POD) catalytic pathway. qRT-PCR was used to confirm the RNA sequencing results for select genes.

Conclusions

A comparison of SFG and LFG transcription profiles revealed modest but important differences in gene expression between the groups. Notably, our results confirm those of previous studies suggesting that genes involved in ethylene, tubulin, and POD pathways play important roles in fiber development. The 22 consistently downregulated DEGs involved in fiber initiation and the 31 consistently upregulated genes involved in fiber elongation are seemingly good candidate genes for improving fiber initiation and elongation in cotton.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5986-5) contains supplementary material, which is available to authorized users.

Characterisation of a rice vacuolar invertase isoform, OsINV2, for growth and yield-related traits

OsINV2, a rice vacuolar invertase isoform, was assessed for its functional roles in plant growth and development with key focus on its agronomic traits such as grain weight, grain filling percentage, grain number and dry weights at various stages until harvest. Lack of differences between the wild-type and the mutants with respect to any of the aforementioned traits tested revealed a possibility of functional compensation of OsINV2 in the mutants conceivably by its isoform. This was confirmed by OsINV2 promoter::GUS studies, where its spatial and temporal expression in the panicle elongation stages showed that although OsINV2 expression was observed from the stage with young panicles ~1 cm in length to the flag leaf stage, significant differences with respect to panicle and spikelet phenotypes between the wild-type and the mutant were not present. However, complement lines displaying an overexpression phenotype of OsINV2 possessed a higher stem non-structural carbohydrate content under both monoculm and normal tillering conditions. A trade-off between the spikelet number and grain weight in the complement lines grown under monoculm conditions was also observed, pointing towards the necessity of OsINV2 regulation for grain yield-related traits.

Overexpression of PsnSuSy1, 2 genes enhances secondary cell wall thickening, vegetative growth, and mechanical strength in transgenic tobacco

KEY MESSAGE

Two homologs PsnSuSy1 and PsnSuSy2 from poplar played largely similar but little distinct roles in modulating sink strength, accelerating vegetative growth and modifying secondary growth of plant. Co-overexpression of them together resulted in small but perceptible additive effects. Sucrose synthase (SuSy) acts as a crucial determinant of sink strength by controlling the conversion of sucrose into UDP-glucose, which is not only the sole precursor for cellulose biosynthesis but also an extracellular signaling molecule for plants growth. Therefore, modification of SuSy activity in plants is of utmost importance. We have isolated two SuSy genes from poplar, PsnSuSy1 and PsnSuSy2, which were preferentially expressed in secondary xylem/phloem. To investigate their functions, T2 tobacco transgenic lines of PsnSuSy1 and PsnSuSy2 were generated and then crossed to generate PsnSuSy1/PsnSuSy2 dual overexpression transgenic lines. SuSy activities in all lines were significantly increased though PsnSuSy1/PsnSuSy2 lines only exhibited slightly higher SuSy activities than either PsnSuSy1 or PsnSuSy2 lines. The significantly increased fructose and glucose, engendered by augmented SuSy activities, caused the alternations of many physiological, biochemical measures and phenotypic traits that include accelerated vegetative growth, thickened secondary cell wall, and increased stem breaking force, accompanied with altered expression levels of related pathway genes. The correlation relationships between SuSy activities and many of these traits were statistically significant. However, differences of almost all traits among three types of transgenic lines were insignificant. These findings clearly demonstrated that PsnSuSy1 and PsnSuSy2 had similar but little distinct functions and insubstantial additive effects on modulating sink strength and affecting allocation of carbon elements among secondary cell wall components.

Cotton fiber elongation requires the transcription factor GhMYB212 to regulate sucrose transportation into expanding fibers

Cotton is white gold across the globe and composed of fiber cells derived from the outer integument of cotton ovules. Fiber elongation uses sucrose as a direct carbon source. The molecular mechanism transcriptionally controlling sucrose transport from ovules into the elongating fibers remains elusive. In this study the involvement of GhMYB212 in the regulation of sucrose transportion into expanding fibers was investigated. GhMYB212 RNAi plants (GhMYB212i) accumulated less sucrose and glucose in developing fibers, and had shorter fibers and a lower lint index. RNA-seq and protein-DNA binding assays revealed that GhMYB212 was closely linked to the pathways of sucrose and starch transportation and metabolism, directly controling the expression of a sucrose transporter gene GhSWEET12. GhSWEET12 RNAi plants (GhSWEET12i) possessed similar fiber phenotypes to those of GhMYB212i. Exogenous sucrose supplementation in ovule cultures did not rescue the shorter fiber phenotype of GhMYB212i and GhSWEET12i. This finding supported the idea that the attenuated rate of sucrose transport from the outer seed coat into the fibers is responsible for the retardation of fiber elongation. Current investigations support the idea that GhMYB212 functions as the main regulator of fiber elongation by controlling the expression of GhSWEET12, and therefore it is important to study cell expansion and sugar transportation during seed development.

Down-Regulating Cucumber Sucrose Synthase 4 (CsSUS4) Suppresses the Growth and Development of Flowers and Fruits

Sucrose synthase (SUS), which catalyzes the reversible conversion of sucrose and uridine diphosphate (UDP) into fructose and UDP-glucose, is a key enzyme in sucrose metabolism in higher plants. In this study, we used reverse genetic approaches and carbohydrate analysis to investigate the role of cucumber sucrose synthase gene 4 (CsSUS4) in the growth and development of sink organs. Transcript analyses showed that CsSUS4 was predominantly expressed in sink organs, particularly in flowers, fruits and roots, and that CsSUS4 protein was localized to companion cells and phloem parenchyma cells. Down-regulation of CsSUS4 expression resulted in a decrease in SUS activity in conjunction with lower hexose, starch and cellulose contents in fruits, and led to an overall reduction in the size and weight of flowers and fruits. Furthermore, CsSUS4 overexpression (OE) lines exhibited increased carbohydrate content, and larger and heavier flowers and fruits. The numbers of multi-petal flowers and multi-carpel fruits were greater in CsSUS4-OE plants compared with wild type and were regulated by MADS-box transcription factor. These results demonstrate that CsSUS4 plays important roles in the growth and development of cucumber flowers and fruits.

Gossypium barbadense and Gossypium hirsutum genomes provide insights into the origin and evolution of allotetraploid cotton

Allotetraploid cotton is an economically important natural-fiber-producing crop worldwide. After polyploidization, Gossypium hirsutum L. evolved to produce a higher fiber yield and to better survive harsh environments than Gossypium barbadense, which produces superior-quality fibers. The global genetic and molecular bases for these interspecies divergences were unknown. Here we report high-quality de novo-assembled genomes for these two cultivated allotetraploid species with pronounced improvement in repetitive-DNA-enriched centromeric regions. Whole-genome comparative analyses revealed that species-specific alterations in gene expression, structural variations and expanded gene families were responsible for speciation and the evolutionary history of these species. These findings help to elucidate the evolution of cotton genomes and their domestication history. The information generated not only should enable breeders to improve fiber quality and resilience to ever-changing environmental conditions but also can be translated to other crops for better understanding of their domestication history and use in improvement.

Gossypium barbadense and Gossypium hirsutum genomes provide insights into the origin and evolution of allotetraploid cotton

Allotetraploid cotton is an economically important natural-fiber-producing crop worldwide. After polyploidization, Gossypium hirsutum L. evolved to produce a higher fiber yield and to better survive harsh environments than Gossypium barbadense, which produces superior-quality fibers. The global genetic and molecular bases for these interspecies divergences were unknown. Here we report high-quality de novo-assembled genomes for these two cultivated allotetraploid species with pronounced improvement in repetitive-DNA-enriched centromeric regions. Whole-genome comparative analyses revealed that species-specific alterations in gene expression, structural variations and expanded gene families were responsible for speciation and the evolutionary history of these species. These findings help to elucidate the evolution of cotton genomes and their domestication history. The information generated not only should enable breeders to improve fiber quality and resilience to ever-changing environmental conditions but also can be translated to other crops for better understanding of their domestication history and use in improvement.

Regulatory Aspects of the Vacuolar CAT2 Arginine Transporter of S. lycopersicum: Role of Osmotic Pressure and Cations

Many proteins are localized at the vacuolar membrane, but most of them are still poorly described, due to the inaccessibility of this membrane from the extracellular environment. This work focused on the characterization of the CAT2 transporter from S. lycopersicum (SlCAT2) that was previously overexpressed in E. coli and reconstituted in proteoliposomes for transport assay as [³H]Arg uptake. The orientation of the reconstituted transporter has been attempted and current data support the hypothesis that the protein is inserted in the liposome in the same orientation as in the vacuole. SlCAT2 activity was dependent on the pH, with an optimum at pH 7.5. SlCAT2 transport activity was stimulated by the increase of internal osmolality from 0 to 175 mOsmol while the activity was inhibited by the increase of external osmolality. K⁺, Na⁺, and Mg²⁺ present on the external side of proteoliposomes at physiological concentrations, inhibited the transport activity; differently, the cations had no effect when included in the internal proteoliposome compartment. This data highlighted an asymmetric regulation of SlCAT2. Cholesteryl hemisuccinate, included in the proteoliposomal membrane, stimulated the SlCAT2 transport activity. The homology model of the protein was built using, as a template, the 3D structure of the amino acid transporter GkApcT. Putative substrate binding residues and cholesterol binding domains were proposed. Altogether, the described results open new perspectives for studying the response of SlCAT2 and, in general, of plant vacuolar transporters to metabolic and environmental changes.

Soluble Acid Invertases Act as Key Factors Influencing the Sucrose/Hexose Ratio and Sugar Receding in Longan ( Dimocarpus longan Lour.) Pulp

Soluble acid invertases (SAIs) cleave sucrose into hexose in vacuoles and play important roles in influencing fruit quality. However, their potential roles in regulating sugar composition and the "sugar receding" process of longan fruits lacked systematic investigations. Our results showed that sucrose/hexose ratios and sugar receding rates of longan pulp varied among cultivars. Analysis of enzymes for sucrose synthesis and cleavage indicated that DlSAI showed the highest negative correlation with sucrose/hexose ratio at both of activity and expression level. Moreover, high SAI activity and DlSAI expression resulted in extremely low sucrose/hexose ratio in 'Luosanmu' longan from development to mature stages and a remarkable loss of sugar in 'Shixia' longan fruits during on-tree preservation. In conclusion, DlSAIs act as key factors influencing sucrose/hexose ratio and sugar receding through transcriptional and enzymatic regulations. These results might help improve the quality of on-tree preserved longan.

Fiber Quality Improvement in Upland Cotton (Gossypium hirsutum L.): Quantitative Trait Loci Mapping and Marker Assisted Selection Application

Genetic improvement in fiber quality is one of the main challenges for cotton breeders. Fiber quality traits are controlled by multiple genes and are classified as complex quantitative traits, with a negative relationship with yield potential, so the genetic gain is low in traditional genetic improvement by phenotypic selection. The availability of Gossypium genomic sequences facilitates the development of high-throughput molecular markers, quantitative trait loci (QTL) fine mapping and gene identification, which helps us to validate candidate genes and to use marker assisted selection (MAS) on fiber quality in breeding programs. Based on developments of high density linkage maps, QTLs fine mapping, marker selection and omics, we have performed trait dissection on fiber quality traits in diverse populations of upland cotton. QTL mapping combined with multi-omics approaches such as, RNA sequencing datasets to identify differentially expressed genes have benefited the improvement of fiber quality. In this review, we discuss the application of molecular markers, QTL mapping and MAS for fiber quality improvement in upland cotton.

The Tonoplastic Inositol Transporter INT1 From Arabidopsis thaliana Impacts Cell Elongation in a Sucrose-Dependent Way

The tonoplastic inositol transporter INT1 is the only known transport protein in Arabidopsis that facilitates myo-inositol import from the vacuole into the cytoplasm. Impairment of the release of vacuolar inositol by knockout of INT1 results in a severe inhibition of cell elongation in roots as well as in etiolated hypocotyls. Importantly, a more strongly reduced cell elongation was observed when sucrose was supplied in the growth medium, and this sucrose-dependent effect can be complemented by the addition of exogenous myo-inositol. Comparing int1 mutants (defective in transport) with mutants defective in myo-inositol biosynthesis (mips1 mutants) revealed that the sucrose-induced inhibition in cell elongation does not just depend on inositol depletion. Secondary effects as observed for altered availability of inositol in biosynthesis mutants, as disturbed membrane turnover, alterations in PIN protein localization or alterations in inositol-derived signaling molecules could be ruled out to be responsible for impairing the cell elongation in int1 mutants. Although the molecular mechanism remains to be elucidated, our data implicate a crucial role of INT1-transported myo-inositol in regulating cell elongation in a sucrose-dependent manner and underline recent reports of regulatory roles for sucrose and other carbohydrate intermediates as metabolic semaphores.

CsINV5, a tea vacuolar invertase gene enhances cold tolerance in transgenic Arabidopsis

BACKGROUND

Vacuolar invertases (VINs) have been reported to regulate plant growth and development and respond to abiotic stresses such as drought and cold. With our best knowledge, the functions of VIN genes little have been reported in tea plant (Camellia sinensis L.). Therefore, it is necessary to develop research in this field.

RESULTS

Here, we identified a VIN gene, CsINV5, which was induced by cold acclimation and sugar treatments in the tea plant. Histochemical assays results showed that the 1154 bp 5'-flanking sequence of CsINV5 drove β-glucuronidase (GUS) gene expression in roots, stems, leaves, flowers and siliques of transgenic Arabidopsis during different developmental stages. Moreover, promoter deletion analysis results revealed that an LTRE-related motif (CCGAAA) and a WBOXHVISO1 motif (TGACT) within the promoter region of CsINV5 were the core cis-elements in response to low temperature and sugar signaling, respectively. In addition, overexpression of CsINV5 in Arabidopsis promoted taproot and lateral root elongation through glucose-mediated effects on auxin signaling. Based on physiological and RNA-seq analysis, we found that overexpression of CsINV5 improved cold tolerance in transgenic Arabidopsis mainly by increasing the contents of glucose and fructose, the corresponding ratio of hexose to sucrose, and the transcription of osmotic-stress-related genes (P5CS1, P5CS2, AtLEA3, COR413-PM1 and COR15B) to adjust its osmotic potential.

CONCLUSIONS

Comprehensive experimental results suggest that overexpression of CsINV5 may enhance the cold tolerance of plant through the modification of cellular sugar compounds contents and osmotic regulation related pathways.

Transcriptional responses of soybean roots to colonization with the root endophytic fungus Piriformospora indica reveals altered phenylpropanoid and secondary metabolism

Piriformospora indica, a root endophytic fungus, has been shown to enhance biomass production and confer tolerance to various abiotic and biotic stresses in many plant hosts. A growth chamber experiment of soybean (Glycine max) colonized by P. indica compared to uninoculated control plants showed that the fungus significantly increased shoot dry weight, nutrient content, and rhizobial biomass. RNA-Seq analyses of root tissue showed upregulation of 61 genes and downregulation of 238 genes in colonized plants. Gene Ontology (GO) enrichment analyses demonstrated that upregulated genes were most significantly enriched in GO categories related to lignin biosynthesis and regulation of iron transport and metabolism but also mapped to categories of nutrient acquisition, hormone signaling, and response to drought stress. Metabolic pathway analysis revealed upregulation of genes within the phenylpropanoid and derivative pathways such as biosynthesis of monolignol subunits, flavonoids and flavonols (luteolin and quercetin), and iron scavenging siderophores. Highly enriched downregulated GO categories included heat shock proteins involved in response to heat, high-light intensity, hydrogen peroxide, and several related to plant defense. Overall, these results suggest that soybean maintains an association with this root endosymbiotic fungus that improves plant growth and nutrient acquisition, modulates abiotic stress, and promotes synergistic interactions with rhizobia.