Sugars Will Eventually Be Exported Transporters Research Articles

Structural and biochemical insights of xylose MFS and SWEET transporters in microbial cell factories: challenges to lignocellulosic hydrolysates fermentation.

The production of bioethanol from lignocellulosic biomass requires the efficient conversion of glucose and xylose to ethanol, a process that depends on the ability of microorganisms to internalize these sugars. Although glucose transporters exist in several species, xylose transporters are less common. Several types of transporters have been identified in diverse microorganisms, including members of the Major Facilitator Superfamily (MFS) and Sugars Will Eventually be Exported Transporter (SWEET) families. Considering that Saccharomyces cerevisiae lacks an effective xylose transport system, engineered yeast strains capable of efficiently consuming this sugar are critical for obtaining high ethanol yields. This article reviews the structure-function relationship of sugar transporters from the MFS and SWEET families. It provides information on several tools and approaches used to identify and characterize them to optimize xylose consumption and, consequently, second-generation ethanol production.

Genome-Wide Identification and Expression Analysis of the SWEET Gene Family in Capsicum annuum L.

Sugars will eventually be exported transporters (SWEETs) are a novel class of sugar transport proteins that play a crucial role in plant growth, development, and response to stress. However, there is a lack of systematic research on SWEETs in Capsicum annuum L. In this study, 33 CaSWEET genes were identified through bioinformatics analysis. The Ka/Ks analysis indicated that SWEET genes are highly conserved not only among peppers but also among Solanaceae species and have experienced strong purifying selection during evolution. The Cis-elements analysis showed that the light-responsive element, abscisic-acid-responsive element, jasmonic-acid-responsive element, and anaerobic-induction-responsive element are widely distributed in the promoter regions of CaSWEETs. The expression pattern analysis revealed that CaSWEETs exhibit tissue specificity and are widely involved in pepper growth, development, and stress responses. The post-transcription regulation analysis revealed that 20 pepper miRNAs target and regulate 16 CaSWEETs through cleavage and translation inhibition mechanisms. The pathogen inoculation assay showed that CaSWEET16 and CaSWEET22 function as susceptibility genes, as the overexpression of these genes promotes the colonization of pathogens, whereas CaSWEET31 functions as a resistance gene. In conclusion, through systematic identification and characteristic analysis, a comprehensive understanding of CaSWEET was obtained, which lays the foundation for further studies on the biological functions of SWEET genes.

The AT-hook protein AHL29 promotes Bacillus subtilis colonization by suppressing SWEET2-mediated sugar retrieval in Arabidopsis roots.

Beneficial Bacillus subtilis (BS) symbiosis could combat root pathogenesis, but it relies on root-secreted sugars. Understanding the molecular control of sugar flux during colonization would benefit biocontrol applications. The SWEET (Sugar Will Eventually Be Exported Transporter) uniporter regulates microbe-induced sugar secretion from roots; thus, its homologs may modulate sugar distribution upon BS colonization. Quantitative polymerase chain reaction revealed that gene transcripts of SWEET2, but not SWEET16 and 17, were significantly induced in seedling roots after 12 h of BS inoculation. Particularly, SWEET2-β-glucuronidase fusion proteins accumulated in the apical mature zone where BS abundantly colonized. Yet, enhanced BS colonization in sweet2 mutant roots suggested a specific role for SWEET2 to constrain BS propagation, probably by limiting hexose secretion. By employing yeast one-hybrid screening and ectopic expression in Arabidopsis protoplasts, the transcription factor AHL29 was identified to function as a repressor of SWEET2 expression through the AT-hook motif. Repression occurred despite immunity signals. Additionally, enhanced SWEET2 expression and reduced colonies were specifically detected in roots of BS-colonized ahl29 mutant. Taken together, we propose that BS colonization may activate repression of AHL29 on SWEET2 transcription that would be enhanced by immunity signals, thereby maintaining adequate sugar secretion for a beneficial Bacillus association.

Molecular Cloning, Expression Analysis, and Functional Analysis of Nine IbSWEETs in Ipomoea batatas (L.) Lam

Sugar Will Eventually be Exported Transporter (SWEET) genes play an important regulatory role in plants’ growth and development, stress response, and sugar metabolism, but there are few reports on the role of SWEET proteins in sweet potato. In this study, nine IbSWEET genes were obtained via PCR amplification from the cDNA of sweet potato. Phylogenetic analysis showed that nine IbSWEETs separately belong to four clades (Clade I~IV) and contain two MtN3/saliva domains or PQ-loop superfamily and six~seven transmembrane domains. Protein interaction prediction showed that seven SWEETs interact with other proteins, and SWEETs interact with each other (SWEET1 and SWEET12; SWEET2 and SWEET17) to form heterodimers. qRT-PCR analysis showed that IbSWEETs were tissue-specific, and IbSWEET1b was highly expressed during root growth and development. In addition to high expression in leaves, IbSWEET15 was also highly expressed during root expansion, and IbSWEET7, 10a, 10b, and 12 showed higher expression in the leaves. The expression of SWEETs showed a significant positive/negative correlation with the content of soluble sugar and starch in storage roots. Under abiotic stress treatment, IbSWEET7 showed a strong response to PEG treatment, while IbSWEET10a, 10b, and 12 responded significantly to 4 °C treatment and, also, at 1 h after ABA, to NaCl treatment. A yeast mutant complementation assay showed that IbSWEET7 had fructose, mannose, and glucose transport activity; IbSWEET15 had glucose transport activity and weaker sucrose transport activity; and all nine IbSWEETs could transport 2-deoxyglucose. These results provide a basis for further elucidating the functions of SWEET genes and promoting molecular breeding in sweet potato.

Genome-Wide Analysis of the SWEET Transporters and Their Potential Role in Response to Cold Stress in Rosa rugosa

Sugar Will Eventually be Exported Transporter (SWEET) proteins are a recently discovered group of efflux transporters that play essential roles in sugar efflux, phloem loading, reproductive tissue development and stress responses. To date, there have been no reports on the Rosa rugosa (R. rugosa) SWEET genes. In this study, we conducted a comprehensive genomic analysis of the SWEET genes, including chromosome localization, phylogenetic comparison, cis-regulatory element analysis, expression pattern analysis in different tissues, expression pattern analysis under cold stress and subcellular localization analysis. A total of 33RrSWEET members were identified and classified into four distinct clades (Clade I, Clade II, Clade III and Clade IV). They were distributed across seven chromosomes and contained cis-regulatory elements associated with hormone and stress responses. The expression of RrSWEETs showed tissue specificity, with higher expression in roots, flowers or pistils compared to other tissues. Furthermore, during the entire cold stress process, the relative expression levels of RrSWEET4, 16 and 20 were significantly upregulated, especially in the roots and stems of R. rugosa. Subcellular localization analysis revealed that RrSWEET4, 16 and 20 were located on the cell membrane. In summary, the results of this study provide a theoretical basis for future research on the functions of RrSWEET genes in R. rugosa and their role in cold tolerance responses.

The Arabidopsis SWEET1 and SWEET2 uniporters recognize similar substrates while differing in subcellular localization

Sugars Will Eventually be Exported Transporters (SWEETs) are central for sugar allocation in plants. The SWEET family has approximately 20 homologs in most plant genomes, and despite extensive research on their structures and molecular functions, it is still unclear how diverse SWEETs recognize different substrates. Previous work using SweetTrac1, a biosensor constructed by the intramolecular fusion of a conformation-sensitive fluorescent protein in the plasma membrane transporter SWEET1 from Arabidopsis thaliana, identified common features in the transporter's substrates. Here, we report SweetTrac2, a new biosensor based on the Arabidopsis vacuole membrane transporter SWEET2, and use it to explore the substrate specificity of this second protein. Our results show that SWEET1 and SWEET2 recognize similar substrates but some with different affinities. Sequence comparison and mutagenesis analysis support the conclusion that the differences in affinity depend on nonspecific interactions involving previously uncharacterized residues in the substrate-binding pocket. Furthermore, SweetTrac2 can be an effective tool for monitoring sugar transport at vacuolar membranes that would be otherwise challenging to study.

Overexpression of GhSWEET42, a SWEET-like gene from cotton, enhances the oil content and seed size

SWEET (‘sugars will eventually be exported transporters’) family genes reportedly play a critical role in sugar translocation and oil biosynthesis in various plant species. However, their functions in cotton are unknown. The present study demonstrated that while GhSWEET42 was widely expressed in different cotton tissues, it had the highest expression level in the developing ovules. Hence, it performs a vital role in seed development. We constructed GhSWEET42 transgenic Arabidopsis lines to verify the biological function of this gene and found that the oil content and weight of the seeds produced by the overexpression lines were 18–23% and 19–20% higher, respectively than those of the wild-type. Gas chromatography–mass spectrometry (GC–MS) analysis revealed that it was mainly a relative increase in unsaturated fatty acids (FAs) that contributed to the relative increase in oil content in the transgenic seeds. Moreover, the latter exhibited comparative upregulation of certain genes associated with FA and triacylglycerol biosynthesis as well as cell expansion. GhSWEET42 might work synergistically with the aforementioned genes. This finding indicates that GhSWEET42 may be essential in oil biosynthesis and seed development in cotton. The results of the present work may facilitate further explorations into the molecular mechanism of cottonseed oil biosynthesis as well as the cultivation of novel oil-rich cotton varieties.

Insights on the SWEET Gene Role in Soluble Sugar Accumulation via the CO2 Fixation Pathway in Forage Maize Under Salt Stress

AbstractRising soil and water salinity endanger plant growth and crop productivity, putting global food security at risk. As plants are sessile, their adaptation to rapidly changing environments is slow, endangering their survival. As a result, mitigation efforts should shift to developing smart crops capable of withstanding dynamic and heterogeneously distributed salinity. Recent breakthroughs in bioinformatics and high throughput genomics can cost-effectively accelerate the introduction of superior varieties for saline regions. Sugar plays an essential role in biomass accumulation and is thus a viable target for forage crop improvement programs. Sugars Will Eventually be Exported Transporter (SWEET) gene family transcribes for source-sink carbon allocation in the form of sugar in higher plants. However, little is known about SWEET’s role in maize's phenotypes of agronomic interest for forage production. Here, through a genome-wide analysis, we identified and characterized 19 SWEET genes that are expressed across various shoot phenotypes. Eleven of the genes are salt-responsive, and ZmSWEET7 is most abundant in high-sugar-yielding varieties compared to low-sugar varieties. Homologous overexpression of the ZmSWEET7 increases the maximum quantum yield of photosystem II photochemistry (FV/FM), CO2 assimilation rate (A), soluble sugar content, and dry matter, with the quantum yield for CO2 fixation efficiency (phiCO2) showing the most significant increase. There is a strong positive association between phiCO2 and soluble sugar content, dry matter, and FV/FM in ZmSWEET7 overexpressing mutants compared to the wild. These findings indicate that ZmSWEET7-mediated CO2 fixation efficiency rather than assimilation rate plays a positive pleiotropic role in C accumulation in the form of sugar or dry matter via increased FV/FM. This work lays a strong foundation for salt-tolerant forage maize genetic improvement.

Genome-Wide Identification and Expression Profiling Analysis of SWEET Family Genes Involved in Fruit Development in Plum (Prunus salicina Lindl).

SWEETs (sugars will eventually be exported transporters) play a vital role in longer-distance sugar transportation, and thus control carbon flow and energy metabolism in plants. SWEET genes have been identified in various plant species, but their functions in fruit development remain uncharacterized. Here, we isolated 15 putative PsSWEETs from the Prunus salicina genome. For further analysis, comprehensive bioinformatics methods were applied to determine the gene structure, chromosome distribution, phylogeny, cis-acting regulatory elements, and expression profiles of PsSWEETs. qRT-PCR analysis suggested that these SWEETs might have diverse functions in the development of plum fruit. The relative expression levels of PsSWEET1 and PsSWEET9 were obviously higher in ripened fruit than the ones in other developmental stages, suggesting their possible roles in the transport and accumulation of sugars in plum fruit. Positive correlations were found between the expression level of PsSWEET3/10/13 and the content of sucrose, and the expression level of PsSWEET2 and the content of fructose, respectively, during the development of 'Furongli' fruit, suggesting their possible roles in the accumulation of sucrose and fructose. The current study investigated the initial genomic characterization and expression patterns of the SWEET gene family in plum, which could provide a foundation for the further understanding of the functional analysis of the SWEET gene family.

Identification of HuSWEET Family in Pitaya (Hylocereus undatus) and Key Roles of HuSWEET12a and HuSWEET13d in Sugar Accumulation.

The sugar composition and content of fruit have a significant impact on their flavor and taste. In pitaya, or dragon fruit, sweetness is a crucial determinant of fruit taste and consumer preference. The sugars will eventually be exported transporters (SWEETs), a novel group of sugar transporters that have various physiological functions, including phloem loading, seed filling, nectar secretion, and fruit development. However, the role of SWEETs in sugar accumulation in pitaya fruit is not yet clear. Here, we identified 19 potential members (HuSWEET genes) of the SWEET family in pitaya and analyzed their conserved motifs, physiochemical characteristics, chromosomal distribution, gene structure, and phylogenetic relationship. Seven highly conserved α-helical transmembrane domains (7-TMs) were found, and the HuSWEET proteins can be divided into three clades based on the phylogenetic analysis. Interestingly, we found two HuSWEET genes, HuSWEET12a and HuSWEET13d, that showed strong preferential expressions in fruits and an upward trend during fruit maturation, suggesting they have key roles in sugar accumulation in pitaya. This can be further roughly demonstrated by the fact that transgenic tomato plants overexpressing HuSWEET12a/13d accumulated high levels of sugar in the mature fruit. Together, our result provides new insights into the regulation of sugar accumulation by SWEET family genes in pitaya fruit, which also set a crucial basis for the further functional study of the HuSWEETs.

Starving the enemy: how plant and microbe compete for sugar on the border.

As the primary energy source for a plant host and microbe to sustain life, sugar is generally exported by Sugars Will Eventually be Exported Transporters (SWEETs) to the host extracellular spaces or the apoplast. There, the host and microbes compete for hexose, sucrose, and other important nutrients. The host and microbial monosaccharide transporters (MSTs) and sucrose transporters (SUTs) play a key role in the "evolutionary arms race". The result of this competition hinges on the proportion of sugar distribution between the host and microbes. In some plants (such as Arabidopsis, corn, and rice) and their interacting pathogens, the key transporters responsible for sugar competition have been identified. However, the regulatory mechanisms of sugar transporters, especially in the microbes require further investigation. Here, the key transporters that are responsible for the sugar competition in the host and pathogen have been identified and the regulatory mechanisms of the sugar transport have been briefly analyzed. These data are of great significance to the increase of the sugar distribution in plants for improvement in the yield.

Camellia oleifera CoSWEET10 Is Crucial for Seed Development and Drought Resistance by Mediating Sugar Transport in Transgenic Arabidopsis.

Sugar transport from the source leaf to the sink organ is critical for seed development and crop yield, as well as for responding to abiotic stress. SWEETs (sugar will eventually be exported transporters) mediate sugar efflux into the reproductive sink and are therefore considered key candidate proteins for sugar unloading during seed development. However, the specific mechanism underlying the sugar unloading to seeds in Camellia oleifera remains elusive. Here, we identified a SWEET gene named CoSWEET10, which belongs to Clade III and has high expression levels in the seeds of C. oleifera. CoSWEET10 is a plasma membrane-localized protein. The complementation assay of CoSWEET10 in SUSY7/ura3 and EBY.VW4000 yeast strains showed that CoSWEET10 has the ability to transport sucrose, glucose, and fructose. Through the C. oleifera seeds in vitro culture, we found that the expression of CoSWEET10 can be induced by hexose and sucrose, and especially glucose. By generating the restoration lines of CoSWEET10 in Arabidopsis atsweet10, we found that CoSWEET10 restored the seed defect phenotype of the mutant by regulating soluble sugar accumulation and increased plant drought tolerance. Collectively, our study demonstrates that CoSWEET10 plays a dual role in promoting seed development and enhancing plant drought resistance as a sucrose and hexose transporter.

Identification and expression analysis of the SWEET genes in radish reveal their potential functions in reproductive organ development.

Sugars produced by photosynthesis provide energy for biological activities and the skeletons for macromolecules; they also perform multiple physiological functions in plants. Sugar transport across plasma membranes mediated by the Sugar Will Eventually be Exported Transporter (SWEET) genes substantially affects these processes. However, the evolutionary dynamics and function of the SWEET genes are largely unknown in radish, an important Brassicaceae species. Genome-wide identification and analysis of the RsSWEET genes from the recently updated radish reference genome was conducted using bioinformatics methods. The tissue-specific expression was analyzed using public RNA-seq data, and the expression levels in the bud, stamens, pistils, pericarps and seeds at 15 and 30days after flowering (DAF) were determined by RT‒qPCR. Thirty-seven RsSWEET genes were identified and named according to their Arabidopsis homologous. They are unevenly distributed across the nine radish chromosomes and were further divided into four clades by phylogenetic analysis. There are 5-7 transmembrane domains and at least one MtN3_slv domain in the RsSWEETs. RNA-seq and RT‒qPCR revealed that the RsSWEETs exhibit higher expression levels in the reproductive organs, indicating that these genes might play vital roles in reproductive organ development. RsSWEET15.1 was found to be especially expressed in siliques according to the RNA-seq data, and the RT‒qPCR results further confirmed that it was most highly expressed levels in the seeds at 30 DAF, followed by the pericarp at 15 DAF, indicating that it is involved in seed growth and development. This study suggests that the RsSWEET genes play vital roles in reproductive organ development and provides a theoretical basis for the future functional analysis of RsSWEETs in radish.

PagSWEET17a Mediates Sugar Transport in Root and Affects Drought Tolerance in Populus alba × P. glandulosa

Sugars are the principal carbon and energy sources and serve as osmotic regulators and radical scavengers, thus playing an important role in plant responses to drought. Sugar transporters steering the distribution of sugar are vital players involved in tolerance to drought. Sugars Will Eventually be Exported Transporters (SWEETs) facilitate both the influx and efflux of mono- and/or disaccharides and control both inter and intracellular distribution of sugars. PagSWEET17a in Populus alba × P. glandulosa is one of four orthologous genes of AtSWEET17 in Arabidopsis. Unlike AtSWEET17, which is a vacuolar localized transporter, PagSWEET17a is localized to the endoplasmic reticulum (ER). Here, the role of PagSWEET17a in poplar responses to drought stress was investigated. PagSWEET17a was specifically expressed in cambium cells in younger root but mainly located in phloem fibers, and xylem vessels and fiber cells in the root undergoing secondary growth. Loss of PagSWEET17a inhibited the growth of roots in poplar seedlings and led to a decreased tolerance to drought. Analysis of sugar profiles revealed that accumulations of predominant sugars were significantly suppressed in both knockout (KO) mutant lines under drought. PagSWEET17a might contribute to poplar tolerance to drought by promoting drought-induced root expansion and diminishing oxidative damages caused by the stress.

Genome-wide identification, characterization and transcriptional profile of the SWEET gene family in Dendrobium officinale

BackgroundDendrobium officinale Kimura et Migo (D. officinale) is a well-known traditional Chinese medicine with high content polysaccharides in stems. The SWEET (Sugars Will Eventually be Exported Transporters) family is a novel class of sugar transporters mediating sugar translocation among adjacent cells of plants. The expression patterns of SWEETs and whether they are associated with stress response in D. officinale remains uncovered.ResultsHere, 25 SWEET genes were screened out from D. officinale genome, most of which typically contained seven transmembrane domains (TMs) and harbored two conserved MtN3/saliva domains. Using multi-omics data and bioinformatic approaches, the evolutionary relationship, conserved motifs, chromosomal location, expression patterns, correlationship and interaction network were further analyzed. DoSWEETs were intensively located in nine chromosomes. Phylogenetic analysis revealed that DoSWEETs were divided into four clades, and conserved motif 3 specifically existed in DoSWEETs from clade II. Different tissue-specific expression patterns of DoSWEETs suggested the division of their roles in sugar transport. In particular, DoSWEET5b, 5c, and 7d displayed relatively high expression levels in stems. DoSWEET2b and 16 were significantly regulated under cold, drought, and MeJA treatment, which were further verified using RT-qPCR. Correlation analysis and interaction network prediction discovered the internal relationship of DoSWEET family.ConclusionsTaken together, the identification and analysis of the 25 DoSWEETs in this study provide basic information for further functional verification in D. officinale.

Genome-Wide Identification of the RsSWEET Gene Family and Functional Analysis of RsSWEET17 in Root Growth and Development in Radish

SWEET (Sugars Will Eventually be Exported Transporter) genes play essential roles in various biological processes, including phloem loading, sugar efflux, plant development and stress response. In this study, a total of 33 RsSWEET gene members were identified in the radish genome. They could be divided into four subfamilies and are distributed on eight radish chromosomes. Cis-acting regulatory element analysis indicated that these RsSWEET genes were potentially involved in the radish growth and development and stress response process, including circadian control and light response and responses to numerous stresses, including low-temperature and drought stress. Transcriptome data analysis revealed that a number of RsSWEET genes exhibited specific expression patterns in different tissues and developmental stages of radish. Moreover, several RsSWEET genes (e.g., RsSWEET2a, RsSWEET3a, RsSWEET16b and RsSWEET17) showed differential expression profiles under various abiotic stresses, including cold, heat, salt, Cd and Pb stress. Remarkably, the RsSWEET17 was specifically expressed in the cambium of radish. RsSWEET17 was heterologously expressed in yeast strain EBY.VW4000, which suggested that it has the ability to transport sugar. Notably, RsSWEET17-overexpressing Arabidopsis plants exhibited excessive root length, greater fresh weight and higher soluble sugar content (SSC) accumulation compared with wild-type (WT) plants, indicating that RsSWEET17 might positively regulate radish taproot development by strategically manipulating sugar accumulation. Collectively, these results clarify the molecular mechanisms underlying RsSWEET-mediated sugar accumulation and root growth and development in radish.

Transcriptome-wide identification and expression profiling of the SWEET family in Bletilla striata and regulation analysis with non-coding RNAs

Polysaccharides are major bioactive ingredients in the medicinal tubers of Bletilla striata (Thunb.) Rchb.f. The SWEET (Sugars Will Eventually Be Exported Transporters) family is widely identified as bidirectional transporters mediating sugar translocation between source and sink tissues in plants. However, to date, SWEET family members have not been reported in B. striata, as well as the roles in sugar transport and B. striata polysaccharide (BSP) accumulation have not been elucidated. Here, by combining multiple RNA-seq datasets, a de novo transcriptome was assembled to identify SWEET genes in B. striata. Seventeen BsSWEETs were found, which were phylogenetically divided into four clades. Most BsSWEETs contain seven transmembrane domains (TMs) composed of two MtN3/saliva domains. Four of the seven TMs were conserved in the B. striata SWEET family. The expression profiles showed that BsSWEET1, 2b and 3a were the most dominant in tubers, leaves, and roots, respectively. Additionally, BsSWEET4, 5, 11 and 12 responded to exogenous MeJA. According to the co-expression pattern and interaction network prediction, BsSWEET2a-BsSWEET2b, BsSWEET4-BsSWEET5, and BsSWEET11-BsSWEET12 pairs were potential dimers formed during functioning. Furthermore, Bst-miR396g/h and a number of long non-coding RNAs (lncRNAs) were predicted to be involved in BsSWEETs regulation. In particularly, based on sequence alignment and qRT-PCR analysis, lncRNA MSTRG.63923 was likely to act as a competitive endogenous RNA (ceRNA) to compete with BsSWEET1 for Bst-miR396g/h. In conclusion, this study, provides comprehensive information about BsSWEETs and is beneficial for further functional analysis of the SWEET family in B. striata.

Genome-Wide Identification and Expression Analysis of the SWEET Gene Family in Annual Alfalfa (Medicago polymorpha).

SWEET (Sugars will eventually be exported transporter) proteins are a group of sugar transporters that are involved in sugar efflux, phloem loading, reproductive development, plant senescence, and stress responses. In this study, 23 SWEET transporter members were identified in the Medicago polymorpha genome, heterogeneously distributed on seven chromosomes. These MpSWEET genes were divided into four subfamilies, which showed similar gene structure and motif composition within the same subfamily. Seventeen MpSWEET genes encode seven transmembrane helices (TMHs), and all MpSWEET proteins possess conserved membrane domains and putative serine phosphorylation sites. Four and three pairs of MpSWEET genes were predicted to be segmentally and tandemly duplicated, respectively, which may have contributed to their evolution of M. polymorpha. The results of microarray and RNA-Seq data showed that some MpSWEET genes were specifically expressed in disparate developmental stages (including seedling stage, early flowering stage, and late flowering stage) or tissues such as flower and large pod. Based on protein network interaction and expression patterns of MpSWEET genes, six MpSWEET genes were selected for further quantitative real-time PCR validation in different stress treatments. qRT-PCR results showed that MpSWEET05, MpSWEET07, MpSWEET12, MpSWEET15, and MpSWEET21 were significantly upregulated for at least two of the three abiotic stress treatments. These findings provide new insights into the complex transcriptional regulation of MpSWEET genes, which facilitates future research to elucidate the function of MpSWEET genes in M. polymorpha and other legume crops.

Genome-Wide Identification, Expression, and Response to Fusarium Infection of the SWEET Gene Family in Garlic (Allium sativum L.).

Proteins of the SWEET (Sugar Will Eventually be Exported Transporters) family play an important role in plant development, adaptation, and stress response by functioning as transmembrane uniporters of soluble sugars. However, the information on the SWEET family in the plants of the Allium genus, which includes many crop species, is lacking. In this study, we performed a genome-wide analysis of garlic (Allium sativum L.) and identified 27 genes putatively encoding clade I-IV SWEET proteins. The promoters of the A. sativum (As) SWEET genes contained hormone- and stress-sensitive elements associated with plant response to phytopathogens. AsSWEET genes had distinct expression patterns in garlic organs. The expression levels and dynamics of clade III AsSWEET3, AsSWEET9, and AsSWEET11 genes significantly differed between Fusarium-resistant and -susceptible garlic cultivars subjected to F. proliferatum infection, suggesting the role of these genes in the garlic defense against the pathogen. Our results provide insights into the role of SWEET sugar uniporters in A. sativum and may be useful for breeding Fusarium-resistant Allium cultivars.

Genome-Wide Identification of the Rose SWEET Gene Family and Their Different Expression Profiles in Cold Response between Two Rose Species.

Sugars Will Eventually be Exported Transporter (SWEET) gene family plays indispensable roles in plant physiological activities, development processes, and responses to biotic and abiotic stresses, but no information is known for roses. In this study, a total of 25 RcSWEET genes were identified in Rosa chinensis 'Old Blush' by genome-wide analysis and clustered into four subgroups based on their phylogenetic relationships. The genomic features, including gene structures, conserved motifs, and gene duplication among the chromosomes of RcSWEET genes, were characterized. Seventeen types of cis-acting elements among the RcSWEET genes were predicted to exhibit their potential regulatory roles during biotic and abiotic stress and hormone responses. Tissue-specific and cold-response expression profiles based on transcriptome data showed that SWEETs play widely varying roles in development and stress tolerance in two rose species. Moreover, the different expression patterns of cold-response SWEET genes were verified by qRT-PCR between the moderately cold-resistant species R. chinensis 'Old Blush' and the extremely cold-resistant species R. beggeriana. Especially, SWEET2a and SWEET10c exhibited species differences after cold treatment and were sharply upregulated in the leaves of R. beggeriana but not R. chinensis 'Old Blush', indicating that these two genes may be the crucial candidates that participate in cold tolerance in R. beggeriana. Our results provide the foundation for function analysis of the SWEET gene family in roses, and will contribute to the breeding of cold-tolerant varieties of roses.