Overexpression of a potato sucrose synthase gene in cotton accelerates leaf expansion, reduces seed abortion, and enhances fiber production

Starch and sucrose metabolism plays an important role in the stem development in Medicago sativa

The forage quality of alfalfa (Medicago sativa ) stems is greater than the leaves. Sucrose hydrolysis provides energy for stem development, with starch being enzymatically converted into sucrose to maintain energy homeostasis. To understand the physiological and molecular networks controlling stem development, morphological characteristics and transcriptome profiles in the stems of two alfalfa cultivars (Zhungeer and WL168) were investigated. Based on transcriptome data, we analysed starch and sugar contents, and enzyme activity related to starch-sugar interconversion. Zhungeer stems were shorter and sturdier than WL168, resulting in significantly higher mechanical strength. Transcriptome analysis showed that starch and sucrose metabolism were significant enriched in the differentially expressed genes of stems development in both cultivars. Genes encoding INV , bglX , HK , TPS and glgC downregulated with the development of stems, while the gene encoding was AMY upregulated. Weighted gene co-expression network analysis revealed that the gene encoding glgC was pivotal in determining the variations in starch and sucrose contents between the two cultivars. Soluble carbohydrate, sucrose, and starch content of WL168 were higher than Zhungeer. Enzyme activities related to sucrose synthesis and hydrolysis (INV, bglX, HK, TPS) showed a downward trend. The change trend of enzyme activity was consistent with gene expression. WL168 stems had higher carbohydrate content than Zhungeer, which accounted for more rapid growth and taller plants. WL168 formed hollow stems were formed during rapid growth, which may be related to the redistribution of carbohydrates in the pith tissue. These results indicated that starch and sucrose metabolism play important roles in the stem development in alfalfa.

Tracking the Variations in Trace Elements, Some Nutrients, Phenolics, and Anthocyanins in Grewia asiatica L. (Phalsa) at Different Fruit Development Stages

Grewia asiatica L. (phalsa) is a very prevalent berry in Pakistan and is consumed extensively as raw or in the form of juice. Here, for the first time, we assessed phalsa from Pakistan in terms of variations in macro and micro minerals, nutrients, and bio-active phyto-constituents including total phenolic and anthocyanin contents at different fruit developmental stages. It was found that the sugars in phalsa increased from D1 (small at the initial fruit setting stage) to D6 development stage (fully ripened fruit) where sugars at D5 (near to fully ripe) and D6 stages were many times greater than at D1, D2 (unripe close to full-size completion), D3 (close to semi ripe), and D4 stage (semi ripened and full-size attainment). Total acidity of was declined in all developmental stages, where the D1 stage displayed maximum and D6 with the lowest acidity. Ascorbic acid was decreased from D1 to D2 and then increased gradually from D3 to D5 stages. At the D6 stage, again a steep decline in ascorbic acid was observed. The total phenolics (mg gallic acid equivalents/100g) at stage D6 were higher (136.02 ± 1.17), whereas D1 being the lowermost in total phenolic content (79.89 ± 1.72). For anthocyanins (mg/100g), an increasing pattern of changes was observed in all stages of phalsa fruit where the D1 stage showed lower (13.97 ± 4.84) anthocyanin contents which then increased gradually at stage D2 (67.79 ± 6.73), but increased sharply at D3 (199.66 ± 4.90), D4 (211.02 ± 18.85), D5 (328.41 ±14.96) and D6 (532.30 ± 8.51) stages. A total of four anthocyanins such as cyanidin, delphidine-3-glucoside, pelargonidin, and malvidin in phalsa were identified using HPLC procedures, and a significant > 90 % DPPH inhibition in phalsa was observed at the D5 and D6 development stages. The macro and micro minerals including Ni, Zn, Fe, Ca, Cu, Mg, Na, P, and K contents were decreased from initial (D1) stage to the final (D6) development stage, while only Fe displayed an increasing trend from the initial to final fruit development stages (D1-D6). Conclusively, these findings could be of great interest for patients who are intended to consume phalsa as adjuvant therapy against diabetes and metabolic syndromes and other diseases involving reactive oxygen species with minimum metal toxicity.

Sucrose synthase gene SUS3 could enhance cold tolerance in tomato

Tomatoes are susceptible to damage from cold temperatures in all stages of growth. Therefore, it is important to identify genetic resources and genes that can enhance tomato's ability to tolerate cold. In this study, a population of 223 tomato accessions was used to identify the sensitivity or tolerance of plants to cold stress. Transcriptome analysis of these accessions revealed that SUS3, a member of the sucrose synthase gene family, was induced by cold stress. We further investigated the role of SUS3 in cold stress by overexpression (OE) and RNA interference (RNAi). Compared with the wild type, SUS3-OE lines accumulated less MDA and electrolyte leakage and more proline and soluble sugar, maintained higher activities of SOD and CAT, reduced superoxide radicals, and suffered less membrane damage under cold. Thus, our findings indicate that SUS3 plays a crucial role in the response to cold stress. This study indicates that SUS3 may serve as a direct target for genetic engineering and improvement projects, which aim to augment the cold tolerance of tomato crops.

Exogenous Sucrose Confers Low Light Tolerance in Tomato Plants by Increasing Carbon Partitioning from Stems to Leaves

Low light (LL) stress adversely affects plant growth and productivity. The role of exogenous sucrose in enhancing plant LL tolerance was investigated by spraying sucrose on tomato (Solanum lycopersicum L.) leaves. This study employed physiological and molecular approaches to identify the underlying mechanisms. Exogenous sucrose activated sucrose hydrolysis-related enzyme activity and upregulated genes encoding sucrose and hexose transporters in mature leaves, decreasing endogenous sucrose levels and promoting sucrose unloading during LL. Stem-related genes associated with sucrose synthesis and transport were also upregulated, enhancing sucrose phloem loading. Furthermore, sucrose from stems activated sucrose unloading in sink leaves, forming a feed-forward loop to sustain sucrose flow during LL. This led to increased nonstructural carbohydrates (NSCs), improved energy metabolism, and enhanced protein synthesis in leaves, ultimately boosting photosynthesis and fruit yield after light recovery. These findings highlight how exogenous sucrose enhances LL tolerance in tomatoes by increasing the transport of NSCs from stems to leaves.

A SNP variation in the Sucrose synthase (SoSUS) gene associated with sugar-related traits in sugarcane

Background

Sugarcane (Saccharum spp.) is an economically significant crop for both the sugar and biofuel industries. Breeding sugarcane cultivars with high-performance agronomic traits is the most effective approach for meeting the rising demand for sugar and biofuels. Molecular markers associated with relevant agronomic traits could drastically reduce the time and resources required to develop new sugarcane varieties. Previous sugarcane candidate gene association analyses have found single nucleotide polymorphism (SNP) markers associated with sugar-related traits. This study aims to validate these associated SNP markers of six genes, including Lesion simulating disease 1 (LSD), Calreticulin (CALR), Sucrose synthase 1 (SUS1), DEAD-box ATP-dependent RNA helicase (RH), KANADI1 (KAN1), and Sodium/hydrogen exchanger 7 (NHX7), in a diverse population in 2-year and two-location evaluations.

Methods

After genotyping of seven targeted SNP markers was performed by PCR Allelic Competitive Extension (PACE) SNP genotyping, the association with sugar-related traits and important cane yield component traits was determined on a set of 159 sugarcane genotypes. The marker-trait relationships were validated and identified by both t-test analysis and an association analysis based on the general linear model.

Results

The mSoSUS1_SNPCh10.T/C and mSoKAN1_SNPCh7.T/C markers that were designed from the SUS1 and KAN1 genes, respectively, showed significant associations with different amounts of sugar-related traits and yield components. The mSoSUS1_SNPCh10.T/C marker was found to have more significant association with sugar-related traits, including pol, CCS, brix, fiber and sugar yield, with p values of 6.08 × 10-6 to 4.35 × 10-2, as well as some cane yield component traits with p values of 1.61 × 10-4 to 3.35 × 10-2. The significant association is consistent across four environments.

Conclusion

Sucrose synthase (SUS) is considered a crucial enzyme involved in sucrose metabolism. This marker is a high potential functional marker that may be used in sugarcane breeding programs to select superior sugarcane with good fiber and high sugar contents.

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.

GhXB38D represses cotton fibre elongation through ubiquitination of ethylene biosynthesis enzymes GhACS4 and GhACO1

Ethylene plays an essential role in the development of cotton fibres. Ethylene biosynthesis in plants is elaborately regulated by the activities of key enzymes, 1-aminocyclopropane-1-carboxylate oxidase (ACO) and 1-aminocyclopropane-1-carboxylate synthase (ACS); however, the potential mechanism of post-translational modification of ACO and ACS to control ethylene synthesis in cotton fibres remains unclear. Here, we identify an E3 ubiquitin ligase, GhXB38D, that regulates ethylene biosynthesis during fibre elongation in cotton. GhXB38D gene is highly expressed in cotton fibres during the rapid elongation stage. Suppressing GhXB38D expression in cotton significantly enhanced fibre elongation and length, accompanied by the up-regulation of genes associated with ethylene signalling and fibre elongation. We demonstrated that GhXB38D interacts with the ethylene biosynthesis enzymes GhACS4 and GhACO1 in elongating fibres and specifically mediates their ubiquitination and degradation. The inhibition of GhXB38D gene expression increased the stability of GhACS4 and GhACO1 proteins in cotton fibres and ovules, resulting in an elevated concentration of ethylene. Our findings highlight the role of GhXB38D as a regulator of ethylene synthesis by ubiquitinating ACS4 and ACO1 proteins and modulating their stability. GhXB38D acts as a negative regulator of fibre elongation and serves as a potential target for enhancing cotton fibre yield and quality through gene editing strategy.

Activation of Gossypium hirsutum ACS6 Facilitates Fiber Development by Improving Sucrose Metabolism and Transport

Cotton fiber yield depends on the density of fiber cell initials that form on the ovule epidermis. Fiber initiation is triggered by MYB-MIXTA-like transcription factors (GhMMLs) and requires a sucrose supply. Ethylene or its precursor ACC (1-aminocyclopropane-1-carboxylic acid) is suggested to affect fiber yield. The Gossypium hirsutum (L.) genome contains 35 ACS genes (GhACS) encoding ACC synthases. Here, we explored the role of a GhACS family member in the regulation of fiber initiation. Expression analyses showed that the GhACS6.3 gene pair was specifically expressed in the ovules during fiber initiation (3 days before anthesis to 5 days post anthesis, -3 to 5 DPA), especially at -3 DPA, whereas other GhACS genes were expressed at very low or undetectable levels. The expression profile of GhACS6.3 during fiber initial development was confirmed by qRT-PCR analysis. Transgenic lines overexpressing GhACS6.3 (GhACS6.3-OE) showed increased ACC accumulation in ovules, which promoted the formation of fiber initials and fiber yield components. This was accompanied by increased transcript levels of GhMML3 and increased transcript levels of genes encoding sucrose transporters and sucrose synthase. These findings imply that GhACS6.3 activation is required for fiber initial development. Our results lay the foundation for further research on increasing cotton fiber production.

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.

mRNA-Seq and miRNA-Seq Analyses Provide Insights into the Mechanism of Pinellia ternata Bulbil Initiation Induced by Phytohormones

Pinellia ternata (Thunb.) Breit (abbreviated as P. ternata) is a plant with an important medicinal value whose yield is restricted by many factors, such as low reproductive efficiency and continuous cropping obstacles. As an essential breeding material for P. ternata growth and production, the bulbils have significant advantages such as a high survival rate and short breeding cycles. However, the location effect, influencing factors, and molecular mechanism of bulbil occurrence and formation have not been fully explored. In this study, exogenously applied phytohormones were used to induce in vitro petiole of P. ternata to produce bulbil structure. Transcriptome sequencing of mRNA and miRNA were performed in the induced petiole (TCp) and the induced bulbil (TCb). Gene Ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed for the identification of key genes and pathways involved in bulbil development. A total of 58,019 differentially expressed genes (DEGs) were identified. The GO and KEGG analysis indicated that DEGs were mainly enriched in plant hormone signal transduction and the starch and sucrose metabolism pathway. The expression profiles of miR167a, miR171a, and miR156a during bulbil induction were verified by qRT-PCR, indicating that these three miRNAs and their target genes may be involved in the process of bulbil induction and play an important role. However, further molecular biological experiments are required to confirm the functions of the identified bulbil development-related miRNAs and targets.

Genome-Wide Identification and Expression Analysis of the Sucrose Synthase Gene Family in Sweet Potato and Its Two Diploid Relatives

Sucrose synthases (SUS; EC 2.4.1.13) encoded by a small multigene family are the central system of sucrose metabolism and have important implications for carbon allocation and energy conservation in nonphotosynthetic cells of plants. Though the SUS family genes (SUSs) have been identified in several plants, they have not been explored in sweet potato. In this research, nine, seven and seven SUSs were identified in the cultivated sweet potato (Ipomoea batatas, 2n = 6x = 90) as well as its two diploid wild relatives I. trifida (2n = 2x = 30) and I. triloba (2n = 2x = 30), respectively, and divided into three subgroups according to their phylogenetic relationships. Their protein physicochemical properties, chromosomal localization, phylogenetic relationship, gene structure, promoter cis-elements, protein interaction network and expression patterns were systematically analyzed. The results indicated that the SUS gene family underwent segmental and tandem duplications during its evolution. The SUSs were highly expressed in sink organs. The IbSUSs especially IbSUS2, IbSUS5 and IbSUS7 might play vital roles in storage root development and starch biosynthesis. The SUSs could also respond to drought and salt stress responses and take part in hormone crosstalk. This work provides new insights for further understanding the functions of SUSs and candidate genes for improving yield, starch content, and abiotic stress tolerance in sweet potatoes.

The transcription factor CitZAT5 modifies sugar accumulation and hexose proportion in citrus fruit

Sugars are fundamental to plant developmental processes. For fruits, the accumulation and proportion of sugars play crucial roles in the development of quality and attractiveness. In citrus (Citrus reticulata Blanco.), we found that the difference in sweetness between mature fruits of "Gongchuan" and its bud sport "Youliang" is related to hexose contents. Expression of a SuS (sucrose synthase) gene CitSUS5 and a SWEET (sugars will eventually be exported transporter) gene CitSWEET6, characterized by transcriptome analysis at different developmental stages of these 2 varieties, revealed higher expression levels in "Youliang" fruit. The roles of CitSUS5 and CitSWEET6 were investigated by enzyme activity and transient assays. CitSUS5 promoted the cleavage of sucrose to hexoses, and CitSWEET6 was identified as a fructose transporter. Further investigation identified the transcription factor CitZAT5 (ZINC FINGER OF ARABIDOPSIS THALIANA) that contributes to sucrose metabolism and fructose transportation by positively regulating CitSUS5 and CitSWEET6. The role of CitZAT5 in fruit sugar accumulation and hexose proportion was investigated by homologous transient CitZAT5 overexpression, -VIGS, and -RNAi. CitZAT5 modulates the hexose proportion in citrus by mediating CitSUS5 and CitSWEET6 expression, and the molecular mechanism explained the differences in sugar composition of "Youliang" and "Gongchuan" fruit.

Girdling promotes tomato fruit enlargement by enhancing fruit sink strength and triggering cytokinin accumulation

Girdling is a horticultural technique that enhances fruit size by allocating more carbohydrates to fruits, yet its underlying mechanisms are not fully understood. In this study, girdling was applied to the main stems of tomato plants 14 days after anthesis. Following girdling, there was a significant increase in fruit volume, dry weight, and starch accumulation. Interestingly, although sucrose transport to the fruit increased, the fruit's sucrose concentration decreased. Girdling also led to an increase in the activities of enzymes involved in sucrose hydrolysis and AGPase, and to an upregulation in the expression of key genes related to sugar transport and utilization. Moreover, the assay of carboxyfluorescein (CF) signal in detached fruit indicated that girdled fruits exhibited a greater ability to take up carbohydrates. These results indicate that girdling improves sucrose unloading and sugar utilization in fruit, thereby enhancing fruit sink strength. In addition, girdling induced cytokinin (CK) accumulation, promoted cell division in the fruit, and upregulated the expression of genes related to CK synthesis and activation. Furthermore, the results of a sucrose injection experiment suggested that increased sucrose import induced CK accumulation in the fruit. This study sheds light on the mechanisms by which girdling promotes fruit enlargement and provides novel insights into the interaction between sugar import and CK accumulation.

Overexpression of the ZmSUS1 gene alters the content and composition of endosperm starch in maize (Zea mays L.)

ZmSUS1 increases the amylose content of maize by regulating the expression of Shrunken2 (Sh2) and Brittle2 (Bt2) which encode the size subunits of endosperm ADP-glucose pyrophosphorylase, and Granule bound starchsynthase1 (GBSS1) and Starch synthase1 (SS1). Cereal crops accumulate starch in seeds as an energy reserve. Sucrose Synthase (SuSy) plays an important role in grain starch synthesis. In this study, ZmSUS1 was transformed into maize inbred line KN5585, and transgenic plants were obtained. Compared with the non-transgenic negative control, the content and activity of SuSy were significantly increased, the amylose content in mature seeds of transgenic maize increased by 41.1-69.2%, the total starch content increased by 5.0-13.5%, the 100-grain weight increased by 19.0-26.2% and the average diameter of starch granules increased by 10.8-17.2%. These results indicated that overexpression of ZmSUS1 can significantly improve the traits of maize seeds and obtain new lines with high amylose content. It was also found that the overexpression of ZmSUS1 may increase the amylose content by altering the expression of endosperm ADP-glucose pyrophosphorylase (AGPase) subunits Shrunken2 (Sh2) and Brittle2 (Bt2). Moreover, the ectopic expression of ZmSUS1 also affected the expression of Granule bound starch synthase1 (GBSS1) and Starch synthase1 (SS1) which encode starch synthase. This study proved the important role of ZmSUS1 in maize starch synthesis and provided a new technology strategy for improving maize starch content and yield.

Improved cotton yield: Can we achieve this goal by regulating the coordination of source and sink?

Cotton is one of the major cash crops globally. It is characterized by determinate growth and multiple fruiting, which makes the source-sink contradiction more obvious. Coordination between source and sink is crucial for normal growth, yield, and quality of cotton. Numerous studies reported how the assimilate transport and distribution under varying environmental cues affected crop yields. However, less is known about the functional mechanism underlying the assimilate transport between source and sink, and how their distribution impacts cotton growth. Here, we provided an overview of the assimilate transport and distribution mechanisms , and discussed the regulatory mechanisms involved in source-sink balance in relation to cotton yield. Therefore, this review enriched our knowledge of the regulatory mechanism involved in source-sink relationship for improved cotton yield.

VaSUS2 confers cold tolerance in transgenic tomato and Arabidopsis by regulation of sucrose metabolism and ROS homeostasis

VaSUS2 enhances cold tolerance of transgenic tomato and Arabidopsis by regulating sucrose metabolism and improving antioxidant enzymes activity. Sucrose synthetase (SUS) is a key enzyme of sugar metabolism, and plays an important role in response to abiotic stress in plant. However, the function of VaSUS2 remains unknown in cold tolerance. Here, the cloning and functional characterization of the plasma membrane-localized VaSUS2 gene isolated from Vitis amurensis was studied. The transcript level of VaSUS2 was up-regulated under cold stress in Vitis amurensis. Heterologous expression of VaSUS2 in tomato increased SUS activity, which promoted the accumulation of glucose and fructose under cold treatment. The transgenic tomato and Arabidopsis exhibited higher levels of antioxidant enzymes activity, lower relative electrolyte leakage (REL), malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content compared to wild type under cold stress. Importantly, the ability of scavenging reactive oxygen species (ROS) in transgenic plants was significantly improved. Moreover, yeast two-hybrid (Y2H) indicated that VaSnRK1 might be a potential interaction protein of VaSUS2. qRT-PCR showed that sucrose metabolism-related genes SlSUS, SlSPS and SlINV were significantly up-regulated in transgenic tomatoes. Meanwhile, the expression levels of antioxidant enzyme genes and cold-related genes CBF1, COR47 and ICE1 were up-regulated in transgenic plants. Taken together, these results suggested that VaSUS2 was involved in cold tolerance by increasing the levels of soluble sugars, improving the activity of antioxidant enzymes, and up-regulating the expression of cold-related genes in transgenic tomatoes and Arabidopsis.

Effects of Polyploidization on Morphology, Photosynthetic Parameters and Sucrose Metabolism in Lily

Polyploidization is widely used in ornamental plant breeding. The polyploids usually produce greater amounts of biomass. However, the alternations to sucrose metabolism that occur in lily during development after polyploidization induced using colchicine are poorly understood. In this study, compared with their allodiploid counterparts, allotetraploid lilies presented a larger total leaf area per plant and slightly delayed flowering time. Moreover, photosynthetic parameter measurements revealed a higher net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and maximum Pn for allotetraploids than for allodiploids. Compared with allodiploids, allotetraploids also showed higher nonstructural carbohydrate (NSC) contents during development according to HILIC-CAD results. The expression levels of sucrose metabolism-related genes were higher in allotetraploids than in allodiploids at the same time points. The expression profiles of several target genes in allotetraploids were distinctly different from those in allodiploids. Susy2/3 exhibited opposite expression profiles in allotetraploids and allodiploids, and the expression profiles of SPS3 and Susy2 were significantly correlated with sucrose content change trends in allodiploids and allotetraploids, respectively.

Potassium regulates diel leaf growth of Brassica napus by coordinating the rhythmic carbon supply and water balance

Carbon and water are two main factors limiting leaf expansion. Restriction of leaf growth by low availability of carbon or water is among the earliest visible effects of potassium (K) deficiency. It is not known how K is involved in regulating the rhythmic supply of these two substrates, which differ remarkably across the day-night cycle, affecting leaf expansion. We investigated the effects of different K regimes on the time courses of leaf expansion, carbon assimilation, carbohydrates, and hydraulic properties of Brassica napus. Potassium supply increased leaf area, predominantly by promoting night-time leaf expansion (>60%), which was mainly associated with increased availability of carbohydrates from photosynthetic carbon fixation and import from old leaves rather than improvement of leaf hydraulics. However, sufficient K improved leaf hydraulic conductance to balance diurnal evaporative water loss and increase the osmotic contribution of water-soluble carbohydrates, thereby maintaining leaf turgor and increasing the daytime expansion rate. The results also indicated an ontogenetic role of K in modifying the amplitude of circadian expansion; almost 80% of the increase in leaf area occurred before the area reached 66.9% of the mature size. Our data provide mechanistic insight into K-mediated diel coordination of rhythmic carbon supply and water balance in leaf expansion.

Screening cellulose synthesis related genes of EgrEXP and EgrHEX in Eucalyptus grandis

Eucalyptus (including Eucalyptus grandis) is an excellent wood forest tree species that provides a large number of plant fiber raw materials for the paper and timber industries. Cellulose, an essential structural component in plant cell walls, is a renewable biomass resource that plays a very important role in nature. There is still a lack of research on the role of gene regulation in cellulose synthesis. To study the genes of cellulose synthesis, the wood chemical indexes of Eucalyptus grandis were analyzed by taking three different parts from the main stem of Eucalyptus grandis as raw materials. The results showed that the cellulose content in the middle of the trunk was significantly higher than that at the chest diameter and at the upper part of the trunk. A total of 296 differentially expressed genes (DEGs) were obtained from the three site by transcriptome, and 19 key candidate genes were related to the synthesis of cellulose in Eucalyptus grandis. EgrEXP1 and EgrHEX4 were overexpressed in 84 K poplar, the content of cellulose and lignin in genetically modified plants was significantly higher than that of wild type 84 K poplar. Also, the average plant height and average root count were significantly higher than those of control plants, and the average diameter of the middle and stem bases were significantly larger than those of control plants. In this study, the genes related to cellulose synthesis in Eucalyptus grandis are studied, which serve as a strong foundation for understanding the molecular regulation of cellulose synthesis in plants.

Molecular Regulation of Cotton Fiber Development: A Review

Cotton (Gossypium spp.) is an economically important natural fiber crop. The quality of cotton fiber has a substantial effect on the quality of cotton textiles. The identification of cotton fiber development-related genes and exploration of their biological functions will not only enhance our understanding of the elongation and developmental mechanisms of cotton fibers but also provide insights that could aid the cultivation of new cotton varieties with improved fiber quality. Cotton fibers are single cells that have been differentiated from the ovule epidermis and serve as a model system for research on single-cell differentiation, growth, and fiber production. Genes and fiber formation mechanisms are examined in this review to shed new light on how important phytohormones, transcription factors, proteins, and genes linked to fiber development work together. Plant hormones, which occur in low quantities, play a critically important role in regulating cotton fiber development. Here, we review recent research that has greatly contributed to our understanding of the roles of different phytohormones in fiber development and regulation. We discuss the mechanisms by which phytohormones regulate the initiation and elongation of fiber cells in cotton, as well as the identification of genes involved in hormone biosynthetic and signaling pathways that regulate the initiation, elongation, and development of cotton fibers.

The OsNAC23-Tre6P-SnRK1a feed-forward loop regulates sugar homeostasis and grain yield in rice

Tre6P (trehalose-6-phosphate) mediates sensing of carbon availability to maintain sugar homeostasis in plants, which underpins crop yield and resilience. However, how Tre6P responds to fluctuations in sugar levels and regulates the utilization of sugars for growth remains to be addressed. Here, we report that the sugar-inducible rice NAC transcription factor OsNAC23 directly represses the transcription of the Tre6P phosphatase gene TPP1 to simultaneously elevate Tre6P and repress trehalose levels, thus facilitating carbon partitioning from source to sink organs. Meanwhile, OsNAC23 and Tre6P suppress the transcription and enzyme activity of SnRK1a, a low-carbon sensor and antagonist of OsNAC23, to prevent the SnRK1a-mediated phosphorylation and degradation of OsNAC23. Thus, OsNAC23, Tre6P, and SnRK1a form a feed-forward loop to sense sugar and maintain sugar homeostasis by transporting sugars to sink organs. Importantly, plants over-expressing OsNAC23 exhibited an elevated photosynthetic rate, sugar transport, and sink organ size, which consistently increased rice yields by 13%-17% in three elite-variety backgrounds and two locations, suggesting that manipulation of OsNAC23 expression has great potential for rice improvement. Collectively, these findings enhance our understanding of Tre6P-mediated sugar signaling and homeostasis, and provide a new strategy for genetic improvement of rice and possibly also other crops.

Exploring the Contribution of Autophagy to the Excess-Sucrose Response in Arabidopsis thaliana

Autophagy is an essential intracellular eukaryotic recycling mechanism, functioning in, among others, carbon starvation. Surprisingly, although autophagy-deficient plants (atg mutants) are hypersensitive to carbon starvation, metabolic analysis revealed that they accumulate sugars under such conditions. In plants, sugars serve as both an energy source and as signaling molecules, affecting many developmental processes, including root and shoot formation. We thus set out to understand the interplay between autophagy and sucrose excess, comparing wild-type and atg mutant seedlings. The presented work showed that autophagy contributes to primary root elongation arrest under conditions of exogenous sucrose and glucose excess but not during fructose or mannitol treatment. Minor or no alterations in starch and primary metabolites were observed between atg mutants and wild-type plants, indicating that the sucrose response relates to its signaling and not its metabolic role. Extensive proteomic analysis of roots performed to further understand the mechanism found an accumulation of proteins essential for ROS reduction and auxin maintenance, which are necessary for root elongation, in atg plants under sucrose excess. The analysis also suggested mitochondrial and peroxisomal involvement in the autophagy-mediated sucrose response. This research increases our knowledge of the complex interplay between autophagy and sugar signaling in plants.

Transcriptome analysis reveals key developmental and metabolic regulatory aspects of oil palm (Elaeis guineensis Jacq.) during zygotic embryo development

BACKGROUND

Oil palm is the most efficient oil-producing crop in the world, and the yield of palm oil is associated with embryonic development. However, a comprehensive understanding of zygotic embryo development at the molecular level remains elusive. In order to address this issue, we report the transcriptomic analysis of zygotic embryo development in oil palm, specifically focusing on regulatory genes involved in important biological pathways.

RESULTS

In this study, three cDNA libraries were prepared from embryos at S1 (early-stage), S2 (middle-stage), and S3 (late-stage). There were 16,367, 16,500, and 18,012 genes characterized at the S1, S2, and S3 stages of embryonic development, respectively. A total of 1522, 2698, and 142 genes were differentially expressed in S1 vs S2, S1 vs S3, and S2 vs S3, respectively. Using Gene Ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis to identify key genes and pathways. In the hormone signaling pathway, genes related to auxin antagonize the output of cytokinin which regulates the development of embryo meristem. The genes related to abscisic acid negatively regulating the synthesis of gibberellin were strongly up-regulated in the mid-late stage of embryonic development. The results were reported the early synthesis and mid-late degradation of sucrose, as well as the activation of the continuous degradation pathway of temporary starch, providing the nutrients needed for differentiation of the embryonic cell. Moreover, the transcripts of genes involved in fatty acid synthesis were also abundantly accumulated in the zygotic embryos.

CONCLUSION

Taken together, our research provides a new perspective on the developmental and metabolic regulation of zygotic embryo development at the transcriptional level in oil palm.

Elshikh M, Jamil A, Nasir JA, Dvořáčková H, Dvořáček J. Genome-wide analysis of sucrose synthase family in soybean and their expression in response to abiotic stress and seed development

The sucrose synthase (SS) is an important enzyme family which play a vital role in sugar metabolism to improve the fruit quality of the plants. In many plant species, the members of SS family have been investigated but the detailed information is not available in legumes particularly and Glycine max specifically. In the present study, we found thirteen SS members (GmSS1-GmSS13) in G. max genome. High conserved regions were present in the GmSS sequences that may due to the selection pressure during evolutionary events. The segmental duplication was the major factor to increase the number of GmSS family members. The identified thirteen GmSS genes were divided into Class I, Class II and Class III with variable numbers of genes in each class. The protein interaction of GmSS gave the co-expression of sucrose synthase with glucose-1-phosphate adenylyltransferase while SLAC and REL test found number of positive sites in the coding sequences of SS family members. All the GmSS family members except GmSS7 and few of class III members, were highly expressed in all the soybean tissues. The expression of the class I members decreased during seed development, whireas, the class II members expression increased during the seed developing, may involve in sugar metabolism during seed development. Solexa sequencing libraries of acidic condition (pH 4.2) stress samples showed that the expression of class I GmSS genes increased 1- to 2-folds in treated samples than control. The differential expression pattern was observed between the members of a paralogous. This study provides detailed genome-wide analysis of GmSS family in soybean that will provide new insights for future evolutionary and soybean breeding to improve the plant growth and development.

Transcriptomic Analysis Reveal the Molecular Mechanisms of Seed Coat Development in Cucurbita pepo L

Cucurbita pepo is one of the earliest cultivated crops. It is native to Central and South America and is now widely cultivated all over the world for its rich nutrition, short growth period, and high yield, which make it suitable for intercropping. Hull-less C. pepo L. (HLCP) is a rare variant in nature that is easier to consume. Its seed has a seed kernel but lacks a seed coat. The molecular mechanism underlying the lack of seed coat development in the HLCP variety is not clear yet. The BGISEQ-500 sequencing platform was used to sequence 18 cDNA libraries of seed coats from hulled C. pepo (CP) and HLCP at three developmental stages (8, 18, and 28 days) post-pollination. We found that lignin accumulation in the seed coat of the HLCP variety was much lower than that of the CP variety. A total of 2,099 DEGs were identified in the CP variety, which were enriched mainly in the phenylpropanoid biosynthesis pathway, amino sugar, and nucleotide sugar metabolism pathways. A total of 1,831 DEGs were identified in the HLCP variety and found to be enriched mainly in the phenylpropanoid biosynthesis and metabolism pathways of starch and sucrose. Among the DEGs, hub proteins (FusA), protein kinases (IRAK4), and several transcription factors related to seed coat development (MYB, bHLH, NAC, AP2/EREBP, WRKY) were upregulated in the CP variety. The relative expression levels of 12 randomly selected DEGs were determined using quantitative real-time PCR analysis and found to be consistent with those obtained using RNA-Seq, with a correlation coefficient of 0.9474. We found that IRAK4 protein kinases, AP2/EREBP, MYB, bHLH, and NAC transcription factors may play important roles in seed coat development, leading to the formation of HLCP.

Integrated Metabolomics and Transcriptome Analyses Unveil Pathways Involved in Sugar Content and Rind Color of Two Sugarcane Varieties

Metabolic composition can have potential impact on several vital agronomic traits, and metabolomics, which represents the bioactive compounds in plant tissues, is widely considered as a powerful approach for linking phenotype-genotype interactions. However, metabolites related to cane traits such as sugar content, rind color, and texture differences in different sugarcane cultivars using metabolome integrated with transcriptome remain largely inconclusive. In this study, metabolome integrated with transcriptome analyses were performed to identify and quantify metabolites composition, and have better insight into the molecular mechanisms underpinning the different cane traits, namely, brix, rind color, and textures in the stems (S) and leaves (L) of sugarcane varieties FN41 and 165402. We also identified metabolites and associated genes in the phenylpropanoid and flavonoid biosynthesis pathways, starch and sucrose metabolism. A total of 512 metabolites from 11 classes, with the vast majority (122) belonging to flavonoids were identified. Moreover, the relatively high amount of D-fructose 6-p, D-glucose6-p and glucose1-p detected in FN41L may have been transported and distributed by source and sink of the cane, and a majority of them reached the stem of sugarcane FN41L, thereby promoting the high accumulation of sugar in FN41S. Observations also revealed that genes such as C4H, CHS, F3H, F3'H, DFR, and FG2 in phenylpropanoid and flavonoid biosynthesis pathways were the major factors impacting the rind color and contrasting texture of FN41 and 165204. Further analysis revealed that weighted gene co-expression network analysis (WGCNA) hub genes and six transcription factors, namely, Tify and NAC, MYB-related, C2C2-Dof, WRKY, and bHLH play a key role in phenylpropanoid biosynthesis, flavone and flavonol biosynthesis, starch and sucrose metabolism. Additionally, metabolites such as L-phenylalanine, tyrosine, sinapaldehyde, pinobanksin, kaempferin, and nictoflorin were the potential drivers of phenotypic differences. Our finding also demonstrated that genes and metabolites in the starch and sucrose metabolism had a significant effect on cane sugar content. Overall, this study provided valuable insight into the molecular mechanisms underpinning high sugar accumulation and rind color in sugarcane, which we believe is important for future sugarcane breeding programs and the selection of high biomass varieties.

Identification and verification of seed development related miRNAs in kernel almond by small RNA sequencing and qPCR

Many studies have investigated the role of miRNAs on the yield of various plants, but so far, no report is available on the identification and role of miRNAs in fruit and seed development of almonds. In this study, preliminary analysis by high-throughput sequencing of short RNAs of kernels from the crosses between almond cultivars 'Sefid' × 'Mamaee' (with small and large kernels, respectively) and 'Sefid' × 'P. orientalis' (with small kernels) showed that the expressions of several miRNAs such as Pdu-miR395a-3p, Pdu-miR8123-5p, Pdu-miR482f, Pdu-miR6285, and Pdu-miR396a were significantly different. These miRNAs targeted genes encoding different proteins such as NYFB-3, SPX1, PGSIP3 (GUX2), GH3.9, and BEN1. The result of RT-qPCR revealed that the expression of these genes showed significant differences between the crosses and developmental stages of the seeds, suggesting that these genes might be involved in controlling kernel size because the presence of these miRNAs had a negative effect on their target genes. Pollen source can influence kernel size by affecting hormonal signaling and metabolic pathways through related miRNAs, a phenomenon known as xenia.

GmFULa improves soybean yield by enhancing carbon assimilation without altering flowering time or maturity

KEY MESSAGE

GmFULa improved soybean yield by enhancing carbon assimilation. Meanwhile, different from known yield-related genes, it did not alter flowering time or maturity. Soybean (Glycine max (L.) Merr.) is highly demanded by a continuously growing human population. However, increasing soybean yield is a major challenge. FRUITFULL (FUL), a MADS-box transcription factor, plays important roles in multiple developmental processes, especially fruit and pod development, which are crucial for soybean yield formation. However, the functions of its homologs in soybean are not clear. Here, through haplotype analysis, we found that one haplotype of the soybean homolog GmFULa (GmFULa-H02) is dominant in cultivated soybeans, suggesting that GmFULa-H02 was highly selected during domestication and varietal improvement of soybean. Interestingly, transgenic overexpression of GmFULa enhanced vegetative growth with more biomass accumulated and ultimately increased the yield but without affecting the plant height or changing the flowering time and maturity, indicating that it enhances the efficiency of dry matter accumulation. It also promoted the yield factors like branch number, pod number and 100-seed weight, which ultimately increased the yield. It increased the palisade tissue cell number and the chlorophyll content to promote photosynthesis and increase the soluble sugar content in leaves and fresh seeds. Furthermore, GmFULa were found to be sublocalized in the nucleus and positively regulate sucrose synthases (SUSs) and sucrose transporters (SUTs) by binding with the conserved CArG boxes in their promoters. Overall, these results showed GmFULa promotes the capacity of assimilation and the transport of the resultant assimilates to increase yield, and provided insights into the link between GmFULa and sucrose synthesis with transport-related molecular pathways that control seed yield.

Antagonism between abscisic acid and gibberellin regulates starch synthesis and corm development in Gladiolus hybridus

Understanding corm development in flower bulbs is of importance for securing the quality of cut flowers and propagation of commercial stocks. Gladiolus is one of the most popular bulb plants worldwide. Its corm development is characterized by starch accumulation. Previous research has shown that phytohormones (especially gibberellin (GA)) are involved in tuber development. However, the relationship between abscisic acid (ABA)/GA and starch during corm development remains unclear. To gain deeper insights into the biological process of corm development, we performed a detailed anatomical characterization of different stages of corm development and analyzed phytohormone levels. Our study showed that corm development is linked to hormones (ABA and GA) and carbohydrates (sucrose and starch). Exogenous hormone treatment and silencing of endogenous hormone biosynthesis genes indicated that ABA positively regulates corm development, while GA acts as an antagonist of ABA function. A sucrose synthase gene (GhSUS2) was shown to be involved in the antagonism between ABA and GA. GhSUS2 was upregulated by ABA and downregulated by GA. The increase in the transcript level of GhSUS2 coincided with the development of corm/cormels. Silencing of GhSUS2 repressed corm development and starch accumulation. In conclusion, we propose that GhSUS2, an essential enzyme in sucrose degradation, is differentially regulated by ABA and GA and controls corm development in Gladiolus.

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.

Reduced expression of a subunit gene of sucrose non-fermenting 1 related kinase, PpSnRK1βγ, confers flat fruit abortion in peach by regulating sugar and starch metabolism

BACKGROUND

Fruit abortion is a major limiting factor for fruit production. In flat peach, fruit abortion is present in the whole tree of some accessions during early fruit development. However, the physiological factors and genetic mechanism underlying flat fruit abortion remain largely elusive.

RESULTS

In this study, we have revealed that the fertilization process was accomplished and the reduction of sucrose and starch contents might result in flat fruit abortion. By combining association and gene expression analysis, a key candidate gene, PpSnRK1βγ, was identified. A 1.67-Mb inversion co-segregated with flat fruit shape altered the promoter activity of PpSnRK1βγ, resulting in much lower expression in aborting flat peach. Ectopic transformation in tomato and transient overexpression in peach fruit have shown that PpSnRK1βγ could increase sugar and starch contents. Comparative transcriptome analysis further confirmed that PpSnRK1βγ participated in carbohydrate metabolism. Subcellular localization found that PpSnRK1βγ was located in nucleus.

CONCLUSIONS

This study provides a possible reason for flat fruit abortion and identified a critical candidate gene, PpSnRK1βγ, that might be responsible for flat fruit abortion in peach. The results will provide great help in peach breeding and facilitate gene identification for fruit abortion in other plant species.

Disruption of Photomorphogenesis Leads to Abnormal Chloroplast Development and Leaf Variegation in Camellia sinensis

Camellia sinensis cv. 'Yanlingyinbiancha' is a leaf-variegated mutant with stable genetic traits. The current study aimed to reveal the differences between its albino and green tissues, and the molecular mechanism underlying the variegation. Anatomic analysis showed the chloroplasts of albino tissues to have no intact lamellar structure. Photosynthetic pigment in albino tissues was significantly lower than that in green tissues, whereas all catechin components were more abundant in the former. Transcriptome analysis revealed most differentially expressed genes involved in the biosynthesis of photosynthetic pigment, photosynthesis, and energy metabolism to be downregulated in albino tissues while most of those participating in flavonoid metabolism were upregulated. In addition, it was found cryptochrome 1 (CRY1) and phytochrome B (PHYB) genes that encode blue and red light photoreceptors to be downregulated. These photoreceptors mediate chloroplast protein gene expression, chloroplast protein import and photosynthetic pigment biosynthesis. Simultaneously, SUS gene, which was upregulated in albino tissues, encodes sucrose synthase considered a biochemical marker for sink strength. Collectively, we arrived to the following conclusions: (1) repression of the biosynthesis of photosynthetic pigment causes albinism; (2) destruction of photoreceptors in albino tissues suppresses photomorphogenesis, leading to abnormal chloroplast development; (3) albino tissues receive sucrose from the green tissues and decompose their own storage substances to obtain the energy needed for survival; and (4) UV-B signal and brassinosteroids promote flavonoid biosynthesis.

Multi-gene metabolic engineering of tomato plants results in increased fruit yield up to 23%

The capacity to assimilate carbon and nitrogen, to transport the resultant sugars and amino acids to sink tissues, and to convert the incoming sugars and amino acids into storage compounds in the sink tissues, are key determinants of crop yield. Given that all of these processes have the potential to co-limit growth, multiple genetic interventions in source and sink tissues, plus transport processes may be necessary to reach the full yield potential of a crop. We used biolistic combinatorial co-transformation (up to 20 transgenes) for increasing C and N flows with the purpose of increasing tomato fruit yield. We observed an increased fruit yield of up to 23%. To better explore the reconfiguration of metabolic networks in these transformants, we generated a dataset encompassing physiological parameters, gene expression and metabolite profiling on plants grown under glasshouse or polytunnel conditions. A Sparse Partial Least Squares regression model was able to explain the combination of genes that contributed to increased fruit yield. This combinatorial study of multiple transgenes targeting primary metabolism thus offers opportunities to probe the genetic basis of metabolic and phenotypic variation, providing insight into the difficulties in choosing the correct combination of targets for engineering increased fruit yield.

Sugar Signaling During Fruit Ripening

Sugars play a key role in fruit quality, as they directly influence taste, and thus consumer acceptance. Carbohydrates are the main resources needed by the plant for carbon and energy supply and have been suggested to be involved in all the important developmental processes, including embryogenesis, seed germination, stress responses, and vegetative and reproductive growth. Recently, considerable progresses have been made in understanding regulation of fruit ripening mechanisms, based on the role of ethylene, auxins, abscisic acid, gibberellins, or jasmonic acid, in both climacteric and non-climacteric fruits. However, the role of sugar and its associated molecular network with hormones in the control of fruit development and ripening is still poorly understood. In this review, we focus on sugar signaling mechanisms described up to date in fruits, describing their involvement in ripening-associated processes, such as pigments accumulation, and their association with hormone transduction pathways, as well as their role in stress-related responses.

Understanding the role of phytohormones in cotton fiber development through omic approaches; recent advances and future directions

Cotton is among the most important fiber crops for the textile-based industry, thanks to its cellulose-rich mature fibers. The fiber initiation and elongation are one of the best models for deciphering mechanisms of single-cell differentiation and growth, that also target of fiber development programs. During the last couple of decades, high yielding omics approaches (genomics, transcriptomics, and proteomics), have helped in the identification of several genes and gene products involved in fiber development along with functional relationship to phytohormones. For example, MYB transcription factor family and Sus gene family have been evidenced by controlling cotton fiber initiation. Most importantly, the biosynthesis, responses, and transporting of phytohormones is documented to participate in the initiation of cotton fibers. Herein, in this review, the reliable genetic evidence by manipulating the above genes in cotton have been summarized to describe the relationships among key phytohormones, transcription factors, proteins, and downstream fiber growth-related genes such as Sus. The effect of other important factors such as ROS, fatty acid metabolism, and actin (globular multi-functional proteins) over fiber development has also been discussed. The challenges and deficiencies in the research of cotton fiber development have been mentioned along with a future perspective to discover new crucial genes using multiple omics analysis.

A Long-Day Photoperiod and 6-Benzyladenine Promote Runner Formation through Upregulation of Soluble Sugar Content in Strawberry

Commercial strawberries are mainly propagated using daughter plants produced on aerial runners because asexual propagation is faster than seed propagation, and daughter plants retain the characteristics of the mother plant. This study was conducted to investigate the effective factors for runner induction, as well as the molecular mechanisms behind the runner induction. An orthogonal test with 4 factors (photoperiod, temperature, gibberellin, and 6-benzyladenine), each with 3 levels was performed. Proteins were also extracted from the crowns with or without runners and separated by two-dimensional electrophoresis. The results of the orthogonal test showed that a long-day (LD) environment was the most influential factor for the runner formation, and 50 mg·L⁻¹ of 6-BA significantly increased the number of runners. A proteomic analysis revealed that 32 proteins were differentially expressed (2-fold, p < 0.05) in the strawberry crowns with and without runners. A total of 16 spots were up-regulated in the crowns with runners induced by LD treatment. Identified proteins were classified into seven groups according to their biological roles. The most prominent groups were carbohydrate metabolism and photosynthesis, which indicated that the carbohydrate content may increase during runner formation. A further analysis demonstrated that the soluble sugar content was positively correlated with the number of runners. Thus, it is suggested that the photoperiod and 6-BA break the dormancy of the axillary buds and produce runners by increasing the soluble sugar content in strawberry.

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.

SH1-dependent maize seed development and starch synthesis via modulating carbohydrate flow and osmotic potential balance

BACKGROUND

As the main form of photoassimilates transported from vegetative tissues to the reproductive organs, sucrose and its degradation products are crucial for cell fate determination and development of maize kernels. Despite the relevance of sucrose synthase SH1 (shrunken 1)-mediated release of hexoses for kernel development, the underlying physiological and molecular mechanisms are not yet well understood in maize (Zea mays).

RESULTS

Here, we identified a new allelic mutant of SH1 generated by EMS mutagenesis, designated as sh1*. The mutation of SH1 caused more than 90% loss of sucrose synthase activity in sh1* endosperm, which resulted in a significant reduction in starch contents while a dramatic increase in soluble sugars. As a result, an extremely high osmolality in endosperm cells of sh1* was generated, which caused kernel swelling and affected the seed development. Quantitative measurement of phosphorylated sugars showed that Glc-1-P in endosperm of sh1* (17 μg g^- 1 FW) was only 5.2% of that of wild-type (326 μg g^- 1 FW). As a direct source of starch synthesis, the decrease of Glc-1-P may cause a significant reduction in carbohydrates that flow to starch synthesis, ultimately contributing to the defects in starch granule development and reduction of starch content.

CONCLUSIONS

Our results demonstrated that SH1-mediated sucrose degradation is critical for maize kernel development and starch synthesis by regulating the flow of carbohydrates and maintaining the balance of osmotic potential.

The protein kinase FaSnRK1α regulates sucrose accumulation in strawberry fruits

In strawberry, sucrose is the major form of carbohydrate translocated from the leaves to the fruits and plays an important role in fruit ripening. As a conserved energy sensor, sucrose nonfermenting-1 (SNF1)-related kinase 1 (SnRK1) plays an important role in plant carbon metabolism. However, evidence that SnRK1 regulates sucrose accumulation in fruits is lacking. In this study, we transiently expressed FaSnRK1α in strawberry fruits and found that overexpression (OE) of the FaSnRK1α gene significantly increased the sucrose content, whereas repression of FaSnRK1α by RNA interference (RNAi) decreased the sucrose content. Further analysis revealed that FaSnRK1α increased the expression of FaSUS1 and FaSUS3 as well as the activity of sucrose synthase (SUS; EC 2.4.1.13) and that FaSPS1 expression and sucrose phosphate synthase (SPS; EC 2.4.1.14) activity were strongly downregulated, which decreased the accumulation of sucrose. However, the expression of FaSPS3, which is reported to contribute to sucrose accumulation, was induced by FaSnRK1α, and FaNI expression and invertase (INV; EC 3.2.1.26) activity were upregulated by FaSnRK1α. In addition, FaSnRK1α positively upregulated the expression of the sucrose transporter (SUT) genes FaSUT1 and FaSUT5 and interacted with FaSUS1, FaSPS1 and FaSPS3 proteins but not with FaSUS3, FaNI, FaSUT1 or FaSUT5 proteins. Overall, FaSnRK1α systematically regulates the expression of the genes and activities of key enzymes involved in the sucrose metabolic pathway and promotes the long-distance transport of sucrose, thereby increasing sucrose accumulation and ultimately promoting fruit ripening. However, the mechanisms by which sucrose transport and degradation are regulated by SnRK1 warrant additional research.

Arabidopsis sucrose synthase localization indicates a primary role in sucrose translocation in phloem

Sucrose synthase (SuSy) is one of two enzyme families capable of catalyzing the first degradative step in sucrose utilization. Several earlier studies examining SuSy mutants in Arabidopsis failed to identify obvious phenotypic abnormalities compared with wild-type plants in normal growth environments, and as such a functional role for SuSy in the previously proposed cellulose biosynthetic process remains unclear. Our study systematically evaluated the precise subcellular localization of all six isoforms of Arabidopsis SuSy via live-cell imaging. We showed that yellow fluorescent protein (YFP)-labeled SuSy1 and SuSy4 were expressed exclusively in phloem companion cells, and the sus1/sus4 double mutant accumulated sucrose under hypoxic conditions. SuSy5 and SuSy6 were found to be parietally localized in sieve elements and restricted only to the cytoplasm. SuSy2 was present in the endosperm and embryo of developing seeds, and SuSy3 was localized to the embryo and leaf stomata. No single isoform of SuSy was detected in developing xylem tissue of elongating stem, the primary site of cellulose deposition in plants. SuSy1 and SuSy4 were also undetectable in the protoxylem tracheary elements, which were induced by the vascular-related transcription factor VND7 during secondary cell wall formation. These findings implicate SuSy in the biological events related to sucrose translocation in phloem.

Improved Yield and Photosynthate Partitioning in AVP1 Expressing Wheat (Triticum aestivum) Plants

A fundamental factor to improve crop productivity involves the optimization of reduced carbon translocation from source to sink tissues. Here, we present data consistent with the positive effect that the expression of the Arabidopsis thaliana H+-PPase (AVP1) has on reduced carbon partitioning and yield increases in wheat. Immunohistochemical localization of H+-PPases (TaVP) in spring wheat Bobwhite L. revealed the presence of this conserved enzyme in wheat vasculature and sink tissues. Of note, immunogold imaging showed a plasma membrane localization of TaVP in sieve element- companion cell complexes of Bobwhite source leaves. These data together with the distribution patterns of a fluorescent tracer and [U14C]-sucrose are consistent with an apoplasmic phloem-loading model in wheat. Interestingly, 14C-labeling experiments provided evidence for enhanced carbon partitioning between shoots and roots, and between flag leaves and milk stage kernels in AVP1 expressing Bobwhite lines. In keeping, there is a significant yield improvement triggered by the expression of AVP1 in these lines. Green house and field grown transgenic wheat expressing AVP1 also produced higher grain yield and number of seeds per plant, and exhibited an increase in root biomass when compared to null segregants. Another agriculturally desirable phenotype showed by AVP1 Bobwhite plants is a robust establishment of seedlings.

Overexpression of a Sucrose Synthase Gene Indirectly Improves Cotton Fiber Quality Through Sucrose Cleavage

The study aims to improve fiber traits of local cotton cultivar through genetic transformation of sucrose synthase (SuS) gene in cotton. Sucrose synthase (SuS) is an important factor that is involved in the conversion of sucrose to fructose and UDP-glucose, which are essential for the synthesis of cell wall cellulose. In the current study, we expressed a synthetic SuS gene in cotton plants under the control of a CaMV35S promoter. Amplification of an 813-bp fragment using gene-specific primers confirmed the successful introduction of SuS gene into the genome of cotton variety CEMB-00. High SuS mRNA expression was observed in two transgenic cotton plants, MA0023 and MA0034, when compared to the expression in two other transgenic cotton plants, MA0035 and MA0038. Experiments showed that SuS mRNA expression was positively correlated with SuS activity at the vegetative (54%) and reproductive stages (40%). Furthermore, location of transgene was found to be at chromosome no. 9 in the form of single insertion, while no signal was evident in non-transgenic control cotton plant when evaluated through fluorescent in situ hybridization and karyotyping analysis. Fiber analyses of the transgenic cotton plants showed increases of 11.7% fiber length, 18.65% fiber strength, and up to 5% cellulose contents. An improvement in the micronaire value of 4.21 was also observed in the MA0038 transgenic cotton line. Scanning electron microscopy (SEM) revealed that the fibers of the SuS transgenic cotton plants were highly spiral with a greater number of twists per unit length than the fibers of the non-transgenic control plants. These results determined that SuS gene expression influenced cotton fiber structure and quality, suggesting that SuS gene has great potential for cotton fiber quality improvement.

Altered sucrose metabolism and plant growth in transgenic Populus tomentosa with altered sucrose synthase PtSS3

Improvement of wood quality is an important focus of forest genetics and breeding research. Sucrose synthase (SS) catalyzes the reaction of sucrose and uridine diphosphate into uridine diphosphate glucose and fructose. It is a key enzyme involved in cell wall formation during secondary growth by providing the UDP-Glucose substrate for cellulose biosynthesis. In this study, we isolated the single-copy gene PtSS3 from the SS gene family of Populus tomentosa and analyzed its structure. To identify its function in secondary growth, we generated 19 transgenic lines of P. tomentosa using PtSS3 overexpression (OE) and artificial microRNA (amiRNA) constructs. We also performed comprehensive analyses of the transgenic P. tomentosa plants, including phenotypic analyses, quantitative real-time PCR, enzyme activity assays and sugar metabolism. We found significantly higher PtSS3 enzyme activity, fructose, and glucose levels and significantly lower sucrose levels in the stems and leaves of OE-PtSS3 plants. The opposite trend was observed in the amiRNA-PtSS3 lines. Gene expression analyses showed that PtSS3 transcript levels in stems and leaves were up-regulated in the OE-PtSS3 lines and down-regulated in the amiRNA-PtSS3 lines, and the OE-PtSS3 plants grew taller than the wild-type and amiRNA-PtSS3 plants. These findings indicate that PtSS3 plays an important role in sucrose metabolism and growth of trees.

The evolutionary history of the sucrose synthase gene family in higher plants

BACKGROUND

Sucrose synthase (SUS) is widely considered a key enzyme participating in sucrose metabolism in higher plants and regarded as a biochemical marker for sink strength in crops. However, despite significant progress in characterizing the physiological functions of the SUS gene family, knowledge of the trajectory of evolutionary processes and significance of the family in higher plants remains incomplete.

RESULTS

In this study, we identified over 100 SUS genes in 19 plant species and reconstructed their phylogenies, presenting a potential framework of SUS gene family evolution in higher plants. Three anciently diverged SUS gene subfamilies (SUS I, II and III) were distinguished based on their phylogenetic relationships and unique intron/exon structures in angiosperms, and they were found to have evolved independently in monocots and dicots. Each subfamily of SUS genes exhibited distinct expression patterns in a wide range of plants, implying that their functional differentiation occurred before the divergence of monocots and dicots. Furthermore, SUS III genes evolved under relaxed purifying selection in dicots and displayed narrowed expression profiles. In addition, for all three subfamilies of SUS genes, the GT-B domain was more conserved than the "regulatory" domain.

CONCLUSIONS

The present study reveals the evolution of the SUS gene family in higher plants and provides new insights into the evolutionary conservation and functional divergence of angiosperm SUS genes.

Distinct cellulose and callose accumulation for enhanced bioethanol production and biotic stress resistance in OsSUS3 transgenic rice

Genetic modification of plant cell walls is an effective approach to reduce lignocellulose recalcitrance in biofuel production, but it may affect plant stress response. Hence, it remains a challenge to reduce biomass recalcitrance and simultaneously enhance stress resistance. In this study, the OsSUS3-transgenic plants exhibited increased cell wall polysaccharides deposition and reduced cellulose crystallinity and xylose/arabinose proportion of hemicellulose, resulting in largely enhanced biomass saccharification and bioethanol production. Additionally, strengthening of the cell wall also contributed to plant biotic resistance. Notably, the transgenic plants increased stress-induced callose accumulation, and promoted the activation of innate immunity, leading to greatly improved multiple resistances to the most destructive diseases and a major pest. Hence, this study demonstrates a significant improvement both in bioethanol production and biotic stress resistance by regulating dynamic carbon partitioning for cellulose and callose biosynthesis in OsSUS3-transgenic plants. Meanwhile, it also provides a potential strategy for plant cell wall modification.

Sucrose Synthase Enhances Hull Size and Grain Weight by Regulating Cell Division and Starch Accumulation in Transgenic Rice

Grain size and weight are two important determinants of grain yield in rice. Although overexpression of sucrose synthase (SUS) genes has led to several improvements on cellulose and starch-based traits in transgenic crops, little is reported about SUS enhancement of hull size and grain weight in rice. In this study, we selected transgenic rice plants that overexpressed OsSUS1-6 genes driven with the maize Ubi promoter. Compared to the controls (wild type and empty vector line), all independent OsSUS homozygous transgenic lines exhibited considerably increased grain yield and grain weights. Using the representative OsSUS3 overexpressed transgenic plants, four independent homozygous lines showed much raised cell numbers for larger hull sizes, consistent with their enhanced primary cell wall cellulose biosynthesis and postponed secondary wall synthesis. Accordingly, the OsSUS3 transgenic lines contained much larger endosperm volume and higher starch levels than those of the controls in the mature grains, leading to increased brown grain weights by 15–19%. Hence, the results have demonstrated that OsSUS overexpression could significantly improve hull size and grain weight by dynamically regulating cell division and starch accumulation in the transgenic rice.

Updates on molecular mechanisms in the development of branched trichome in Arabidopsis and nonbranched in cotton

Trichomes are specialized epidermal cells and a vital plant organ that protect plants from various harms and provide valuable resources for plant development and use. Some key genes related to trichomes have been identified in the model plant Arabidopsis thaliana through glabrous mutants and gene cloning, and the hub MYB-bHLH-WD40, consisting of several factors including GLABRA1 (GL1), GL3, TRANSPARENT TESTA GLABRA1 (TTG1), and ENHANCER OF GLABRA3 (EGL3), has been established. Subsequently, some upstream transcription factors, phytohormones and epigenetic modification factors have also been studied in depth. In cotton, a very important fibre and oil crop globally, in addition to the key MYB-like factors, more important regulators and potential molecular mechanisms (e.g. epigenetic modifiers, distinct metabolic pathways) are being exploited during different fibre developmental stages. This occurs due to increased cotton research, resulting in the discovery of more complex regulation mechanisms from the allotetraploid genome of cotton. In addition, some conservative as well as specific mediators are involved in trichome development in other species. This study summarizes molecular mechanisms in trichome development and provides a detailed comparison of the similarities and differences between Arabidopsis and cotton, analyses the possible reasons for the discrepancy in identification of regulators, and raises future questions and foci for understanding trichome development in more detail.

Differential Proteomics Based on TMT and PRM Reveal the Resistance Response of Bambusa pervariabilis × Dendrocalamopisis grandis Induced by AP-Toxin

Bambusa pervariabilis McClure × Dendrocalamopsis grandis (Q.H.Dai & X.l.Tao ex Keng f.) Ohrnb. blight is a widespread and dangerous forest fungus disease, and has been listed as a supplementary object of forest phytosanitary measures. In order to study the control of B. pervariabilis × D. grandis blight, this experiment was carried out. In this work, a toxin purified from the pathogen Arthrinium phaeospermum (Corda) Elli, which causes blight in B. pervariabilis × D. grandis, with homologous heterogeneity, was used as an inducer to increase resistance to B. pervariabilis × D. grandis. A functional analysis of the differentially expressed proteins after induction using a tandem mass tag labeling technique was combined with mass spectrometry and liquid chromatography mass spectrometry in order to effectively screen for the proteins related to the resistance of B. pervariabilis × D. grandis to blight. After peptide labeling, a total of 3320 unique peptides and 1791 quantitative proteins were obtained by liquid chromatography mass spectrometry analysis. Annotation and enrichment analysis of these peptides and proteins using the Gene ontology and Kyoto Encyclopedia of Genes and Genomes databases with bioinformatics software show that the differentially expressed protein functional annotation items are mainly concentrated on biological processes and cell components. Several pathways that are prominent in the Kyoto Encyclopedia of Genes and Genomes annotation and enrichment include metabolic pathways, the citrate cycle, and phenylpropanoid biosynthesis. In the Protein-protein interaction networks four differentially expressed proteins-sucrose synthase, adenosine triphosphate-citrate synthase beta chain protein 1, peroxidase, and phenylalanine ammonia-lyase significantly interact with multiple proteins and significantly enrich metabolic pathways. To verify the results of tandem mass tag, the candidate proteins were further verified by parallel reaction monitoring, and the results were consistent with the tandem mass tag data analysis results. It is confirmed that the data obtained by tandem mass tag technology are reliable. Therefore, the differentially expressed proteins and signaling pathways discovered here is the primary concern for subsequent disease resistance studies.

Senescence-induced expression of ZmSUT1 in cotton delays leaf senescence while the seed coat-specific expression increases yield

Sink-specific expression of a sucrose transporter protein gene from the C₄ plant maize can promote carbohydrate accumulation in target tissues and increase both fiber and seed yield of cotton. Sucrose is the principal form of photosynthetic products transported from source tissue to sink tissue in higher plants. Enhancing the partition of carbohydrate to the target organ is a promising way to improve crop productivity. The C₄ plant Zea mays exhibits a substantially higher rate of export of photosynthates than many C₃ plants, and its sucrose transporter protein ZmSut1 displays important role in sucrose allocation. To investigate how use of ZmSUT1 gene to increase the fiber and seed yield of cotton, in this study, we expressed the gene in cotton under a senescence-inducible promoter PSAG12 and a seed coat-specific promoter BAN, respectively. We show that senescence-induced expression of ZmSUT1 results in an increase of sugar accumulation in leaves. Although the leaf senescence was postponed in PSAG12::ZmSUT1 cotton, the photosynthetic rate of the leaves was decreased. In contrast, seed coat-specific expression of the gene leads to an increase of sugar accumulation in fibers and bolls, and the leaf of transgenic BAN::ZmSUT1 cotton displayed higher photosynthetic capacity than the wild type. Importantly, both fiber and seed yield of transgenic BAN::ZmSUT1 cotton are significantly enhanced. Our data indicate the potential of enhancing yield of carbohydrate crops by the regulation of sugar partitioning.