SWEET Gene Family Research Articles

Comprehensive Identification and Expression Profiling of Lipoxygenase Genes in Sweet Cherry During Fruit Development

Lipoxygenase (LOX) is involved in the oxidation of fatty acids in plants and is a ubiquitous oxygenase that plays an important role in the process of plant resistance to adversity. In this study, the LOX gene family in the sweet cherry genome was identified by bioinformatics methods, the chromosomal mapping of different LOX genes was carried out, and the homology alignment and functional domain analysis of the encoded proteins were performed. The results showed that there were nine LOX gene sequences in the sweet cherry LOX gene family, and the subcellular localization was mainly located in the cytoplasm, chloroplast, or plasma membrane, and was concentrated on chromosomes 1, 2, 3, 4, 6, and 8. During the ripening process of sweet cherry fruits, the LOX gene family showed five different expression patterns, the expression peak of different LOX genes reached the peak of expression at a specific development period, all LOX genes jointly promoted the growth and development of fruits, the enzyme activities of LOX in different varieties of early and late ripening cherries exhibited great differences during the development process, and the results of volatile content in the later stages also showed that different varieties of cherries had their specificity. The results of this study provide a theoretical basis for further revealing the specific functions of LOX gene family members in sweet cherry.

Proteomics and transcriptomic analyses provide new insights into the pectin polysaccharide biosynthesis in Premna puberula Pamp

Premna puberula Pamp. is a plant with similarities to both food and medicine, which has attracted the attention of researchers because of the rich pectin in its leaves. However, the mechanism of efficient pectin accumulation remains unclear. Through transcriptomic and proteomic analyses, this study investigated the differentially expressed genes and proteins associated with pectin during various developmental stages of P. puberula. The combined omics approach revealed that the majority of differential genes are mainly involved in the anabolic metabolism of primary and secondary metabolites. Notable differential pathways include starch and sucrose metabolism, amino acid sugar metabolism, and nucleotide sugar metabolism. The SWEET gene family was identified and analyzed, leading to the cloning of PpSWEET15 and subcellular localization. Overexpression of PpSWEET15 resulted in a significant decrease in sucrose content in leaves from 134.44 μg·g−1 to <10 μg·g−1. Glucose content decreased from 407.75 μg·g−1 to 318.38 μg·g−1, while fructose levels showed no significant difference between the two groups of leaves. This comprehensive transcriptomic and proteomic analysis provides valuable insights into the molecular mechanisms underlying the efficient accumulation of pectin in P. puberula.

Genome wide identification of BjSWEET gene family and drought response analysis of BjSWEET12 and BjSWEET17 genes in Brassica juncea

BackgroundSugars Will Eventually be Exported Transporter (SWEET) gene family is a unique type of sugar transporter that plays a vital role in metabolic regulation, growth, development, and stress response in multiple species. This study aimed to systematically identify the SWEET gene family members and detect the regulation of gene expression and their potential roles of the SWEET gene family in Brassica juncea.ResultsA total of 66 BjSWEET (Brassica juncea Sugar Will Eventually be Exported Transporter) genes distributed across 17 chromosomes were identified. The gene structure and motifs were relatively conserved, with all members containing the MtN3/saliva domain. Phylogenetic analysis revealed that the SWEET gene family can be classified into four subfamilies (Clades I, II, III, and IV). Collinearity analysis revealed that there were 118 pairs of segment duplicates, indicating that some BjSWEET genes were obtained via segmental duplication. The promoter regions of the BjSWEET genes contained many plant hormone-related response elements, stress-related response elements, growth and development elements, and light-responsive regulatory elements. Furthermore, analysis of the expression profiles revealed that the expression levels of the BjSWEET genes differed among the eight different tissues. qRT‒PCR analysis of six selected BjSWEET genes revealed that the expression levels of BjSWEET17.2, BjSWEET17.4, BjSWEET12.2, and BjSWEET12.3 were significantly upregulated under drought treatment, suggesting that these genes may respond to drought stress in B. juncea.ConclusionThis study systematically identified and analyzed the SWEET gene family members in B. juncea for the first time, laying the foundation for further research on the molecular mechanisms of drought resistance in B. juncea and providing theoretical guidance for the application of these genes in other species.

The potato sugar transporter SWEET1g affects apoplasmic sugar ratio and phloem-mobile tuber- and flower-inducing signals.

The main phloem loader in potato, sucrose transporter StSUT1, is co-expressed with two members of the SWEET gene family: StSWEET11b, a clade III member of SWEET carriers assumed to be involved in sucrose efflux, and StSWEET1g, a clade I member involved in glucose efflux into the apoplast that physically interacts with StSUT1. We investigated the functionality of SWEET carriers via uptake experiments with fluorescent glucose or sucrose analogs. Inhibition or overexpression of StSWEET1g/SlSWEET1e affected tuberization and flowering in transgenic potato plants. Isolation of the apoplasmic fluid by vacuum infiltration centrifugation revealed changes in the apoplasmic hexose composition and mono-to-disaccharide ratio, affecting sink strength. Down-regulation of StSWEET1g expression affected the expression of SP6A, a tuberigen, and miR172 under LD conditions, leading to early flowering and tuberization. A systematic screen for StSWEET1g-interacting protein partners revealed several proteins affecting cell wall integrity and strengthening. StSWEET1g and the main interaction partners were strongly down-regulated during tuber development. We discuss whether StSWEET1g activity might be linked to cell wall remodeling during tuber development and the switch from apoplasmic to symplasmic phloem unloading.

Expression Profiling Analysis of the SWEET Gene Family in In Vitro Pitaya Under Low-Temperature Stress and Study of Its Cold Resistance Mechanism.

Pitaya (Hylocereus undatus) fruit is an attractive, nutrient-rich tropical fruit with commercial value. However, low-temperature stress severely affects the yield and quality of pitaya. The relevant mechanisms involved in the response of pitaya to low-temperature stress remain unclear. To study whether the SWEET gene family mediates the response of H. undatus to low-temperature stress and the related mechanisms, we performed genome-wide identification of the SWEET gene family in pitaya, and we used 'Baiyulong' tissue-cultured plantlets as material in the present study. We identified 28 members of the SWEET gene family from the H. undatus genome and divided these family members into four groups. Members of this gene family presented some differences in the sequences of introns and exons, but the gene structure, especially the motifs, presented relatively conserved characteristics. The promoter regions of most HuSWEETs have multiple stress- or hormone-related cis-elements. Three duplicated gene pairs were identified, including one tandem duplication gene and two fragment duplication gene pairs. The results revealed that the SWEET genes may regulate the transport and distribution of soluble sugars in plants; indirectly regulate the enzyme activities of CAT, POD, and T-SOD through its expression products; and are involved in the response of pitaya to low-temperature stress and play vital roles in this process. After ABA and MeJA treatment, the expression of HuSWEETs changed significantly, and the cold stress was also alleviated. This study elucidated the molecular mechanism and physiological changes in the SWEET gene in sugar metabolism and distribution of pitaya when it experiences low-temperature stress and provided a theoretical basis for cold-resistant pitaya variety breeding.

Genome-wide identification and expression analysis of the SWEET gene family in sweet sorghum (Sorghum dochna) and the role of SdSWEET01 in sugar transport

The SWEET sugar transporter plays a fundamental role in plant growth and development. In this study, 18 SWEET genes were identified from sweet sorghum (Sorghum dochna), encoding proteins with 231–336 amino acids, molecular weights from 25.15 to 35.69 kDa, and isoelectric points ranging between 6.41 and 9.69. Phylogenetic analysis categorized these proteins into four distinct subgroups. Examination of spatial expression patterns demonstrated that SdSWEET genes were expressed in a tissue-specific manner. Furthermore, their involvement in responses to various abiotic stresses, including cold, heat, drought, and salinity was observed. A yeast complementation assay verified that SdSWEET01, located on the plasma membrane, selectively transported glucose, sucrose, and galactose, while excluding fructose. Transgenic Arabidopsis expressing SdSWEET01 exhibited enhanced sugar absorption compared to wild-type plants, resulting in increased sensitivity and growth inhibition under high-sugar conditions. The study provides a detailed functional characterization of SdSWEET genes and emphasizes the critical role of SdSWEET01 in regulating sugar transport.

Genome‑wide identification of the SWEET gene family in grape (Vitis vinifera L.) and expression analysis of VvSWEET14a in response to water stress.

The online version contains supplementary material available at 10.1007/s12298-024-01501-1.

Exploring salt tolerance mechanisms using machine learning for transcriptomic insights: case study in Spartina alterniflora.

Salt stress poses a significant threat to global cereal crop production, emphasizing the need for a comprehensive understanding of salt tolerance mechanisms. Accurate functional annotations of differentially expressed genes are crucial for gaining insights into the salt tolerance mechanism. The challenge of predicting gene functions in under-studied species, especially when excluding infrequent GO terms, persists. Therefore, we proposed the use of NetGO 3.0, a machine learning-based annotation method that does not rely on homology information between species, to predict the functions of differentially expressed genes under salt stress. Spartina alterniflora, a halophyte with salt glands, exhibits remarkable salt tolerance, making it an excellent candidate for in-depth transcriptomic analysis. However, current research on the S. alterniflora transcriptome under salt stress is limited. In this study we used S. alterniflora as an example to investigate its transcriptional responses to various salt concentrations, with a focus on understanding its salt tolerance mechanisms. Transcriptomic analysis revealed substantial changes impacting key pathways, such as gene transcription, ion transport, and ROS metabolism. Notably, we identified a member of the SWEET gene family in S. alterniflora, SA_12G129900.m1, showing convergent selection with the rice ortholog SWEET15. Additionally, our genome-wide analyses explored alternative splicing responses to salt stress, providing insights into the parallel functions of alternative splicing and transcriptional regulation in enhancing salt tolerance in S. alterniflora. Surprisingly, there was minimal overlap between differentially expressed and differentially spliced genes following salt exposure. This innovative approach, combining transcriptomic analysis with machine learning-based annotation, avoids the reliance on homology information and facilitates the discovery of unknown gene functions, and is applicable across all sequenced species.

Sweet cherry TCP gene family analysis reveals potential functions of PavTCP1, PavTCP2 and PavTCP3 in fruit light responses

BackgroundTCP proteins are plant specific transcription factors that play important roles in plant growth and development. Despite the known significance of these transcription factors in general plant development, their specific role in fruit growth remains largely uncharted. Therefore, this study explores the potential role of TCP transcription factors in the growth and development of sweet cherry fruits.ResultsThirteen members of the PavTCP family were identified within the sweet cherry plant, with two, PavTCP1 and PavTCP4, found to contain potential target sites for Pav-miR159, Pav-miR139a, and Pav-miR139b-3p. Analyses of cis-acting elements and Arabidopsis homology prediction analyses that the PavTCP family comprises many light-responsive elements. Homologs of PavTCP1 and PavTCP3 in Arabidopsis TCP proteins were found to be crucial to light responses. Shading experiments showed distinct correlation patterns between PavTCP1, 2, and 3 and total anthocyanins, soluble sugars, and soluble solids in sweet cherry fruits. These observations suggest that these genes may contribute significantly to sweet cherry light responses. In particular, PavTCP1 could play a key role, potentially mediated through Pav-miR159, Pav-miR139a, and Pav-miR139b-3p.ConclusionThis study is the first to unveil the potential function of TCP transcription factors in the light responses of sweet cherry fruits, paving the way for future investigations into the role of this transcription factor family in plant fruit development.

Plasma membrane-localized hexose transporter OsSWEET1b, affects sugar metabolism and leaf senescence.

OsSWEET1b is a hexose transporter protein, which localized in cell membranes and interacting with itself to form homodimer and knockout of OsSWEET1b resulted in reduced leaves sugar content and accelerating leaf senescence. In the rice genome, the SWEET gene family contains 21 homologous members, but the role of some of them in rice growth and development is still unknown. The function of the sugar transporter OsSWEET1b protein in rice was identified in this research. Expression analysis showed that the expression levels of OsSWEET1b in leaves were higher than that in other tissues. The hexose transport experiment confirmed that OsSWEET1b has glucose and galactose transporter activity in yeast. Subcellular localization indicates that OsSWEET1b protein was targeted to the plasma membrane and BiFC analysis showed that OsSWEET1b interacts with itself to form homodimers. Functional analysis demonstrated that the ossweet1b mutant plants were have reduced the sucrose, glucose, fructose, starch and galactose contents, and induced carbon starvation-related gene expression, which might lead to carbon starvation in leaves at filling stage. The ossweet1b knockout plants showed decreased chlorophyll content and antioxidant enzyme activity, and increased ROS accumulation in leaves, leading to leaf cell death and premature senescence phenotype at filling stage. In ossweet1b mutants, the leaf senescence-related gene expression levels were increased and the abundance of photosynthesis-related proteins was decreased. Loss of OsSWEET1b were affected the starch, sucrose metabolism and carbon fixation in photosynthetic organelles pathway by RNA-seq analysis. The destruction of OsSWEET1b function will cause sugar starvation, decreased photosynthesis and leaf senescence, which leading to reduced rice yield. Collectively, our results suggest that the OsSWEET1b plays a key role in rice leaves carbohydrate metabolism and leaf senescence.

The SWEET gene family in watermelon: genome-wide identification, phylogeny, duplication and expression analyses in male sterile buds and under sucrose, fructose and glucose treatments

The SWEET gene family in watermelon: genome-wide identification, phylogeny, duplication and expression analyses in male sterile buds and under sucrose, fructose and glucose treatments

An Insight of Betula platyphylla SWEET Gene Family through Genome-Wide Identification, Expression Profiling and Function Analysis of BpSWEET1c under Cold Stress.

SWEET proteins play important roles in plant growth and development, sugar loading in phloem and resistance to abiotic stress through sugar transport. In this study, 13 BpSWEET genes were identified from birch genome. Collinearity analysis showed that there were one tandem repeating gene pair (BpSWEET1b/BpSWEET1c) and two duplicative gene pairs (BpSWEET17a/BpSWEET17b) in the BpSWEET gene family. The BpSWEET gene promoter regions contained several cis-acting elements related to stress resistance, for example: hormone-responsive and low-temperature-responsive cis-elements. Analysis of transcriptome data showed that BpSWEET genes were highly expressed in several sink organs, and the most BpSWEET genes were rapidly up-regulated under cold stress. BpSWEET1c, which was highly expressed in cold stress, was selected for further analysis. It was found that BpSWEET1c was located on the cell membrane. After 6 h of 4 °C stress, sucrose content in the leaves and roots of transient overexpressed BpSWEET1c was significantly higher than that of the control. MDA content in roots was significantly lower than that of the control. These results indicate that BpSWEET1c may play a positive role in the response to cold stress by promoting the metabolism and transport of sucrose. In conclusion, 13 BpSWEET genes were identified from the whole genome level. Most of the SWEET genes of birch were expressed in the sink organs and could respond to cold stress. Transient overexpression of BpSWEET1c changed the soluble sugar content and improved the cold tolerance of birch.

Actin-Depolymerizing Factor Gene Family Analysis Revealed That CsADF4 Increased the Sensitivity of Sweet Orange to Bacterial Pathogens.

The actin-depolymerizing factor (ADF) gene family regulates changes in actin. However, the entire ADF family in the sweet orange Citrus sinensis has not been systematically identified, and their expressions in different organs and biotic stress have not been determined. In this study, through phylogenetic analysis of the sweet orange ADF gene family, seven CsADFs were found to be highly conserved and sparsely distributed across the four chromosomes. Analysis of the cis-regulatory elements in the promoter region showed that the CsADF gene had the potential to impact the development of sweet oranges under biotic or abiotic stress. Quantitative fluorescence analysis was then performed. Seven CsADFs were differentially expressed against the invasion of Xcc and CLas pathogens. It is worth noting that the expression of CsADF4 was significantly up-regulated at 4 days post-infection. Subcellular localization results showed that CsADF4 was localized in both the nucleus and the cytoplasm. Overexpression of CsADF4 enhanced the sensitivity of sweet orange leaves to Xcc. These results suggest that CsADFs may regulate the interaction of C. sinensis and bacterial pathogens, providing a way to further explore the function and mechanisms of ADF in the sweet orange.

GmMFT: a potential step forward in soybean breeding for high oil and yield.

This article is a Commentary on Cai et al. (2023), 239: 905–919.

Genome-Wide Identification of the Sweet Orange bZIP Gene Family and Analysis of Their Expression in Response to Infection by Penicillium digitatum

(1) Background: The sweet orange (Citrus sinensis) is the most widely cultivated and productive citrus fruit in the world, with considerable economic value and good prospects for development. However, post-harvest storage and transport of the fruit are often affected by infestation by Penicillium species, leading to many losses. (2) Methods: In this study, the family of bZIP genes from the whole genome of sweet orange was identified and analyzed in detail in terms of gene structure, physicochemical properties, protein structure, conserved structural domains, chromosomal positioning, and promoter analysis using bioinformatic analysis, in addition to an analysis of the expression patterns of the fruit following Penicillium infection. (3) Results: In this study, 50 CsbZIP genes were identified from the sweet orange genome. In silico analysis showed that Cs_ont_3g005140 was presumably localized in the chloroplasts, while the rest of the family members were located in the nucleus. Phylogenetic trees of grape, apple, Arabidopsis, and sweet orange were constructed on the basis of evolutionary relationships and divided into 16 subfamilies. Conserved motif analysis showed that all CsbZIP family genes encode proteins containing the highly conserved Motif 1. Promoter prediction analysis showed the chromosomal positioning, and the covariance analysis showed that the 50 CsbZIPs were unevenly distributed on nine chromosomes, with 10 pairs of duplicated genes. In the analysis of expression patterns, 11 of the 50 CsbZIP genes were not expressed, 12 were upregulated, 27 were downregulated, and five of the upregulated genes were highly expressed. (4) Conclusions: In this study, two CsbZIP members were each closely related to two Arabidopsis thaliana genes associated with salt stress. The functions of the replicated and re-differentiated CsbZIP homologs (Cs_ont_1g027160 and Cs_ont_8g020880) divergee further, with one responding to inoculation by Penicillium and the other not doing so. Five genes associated with sweet orange in response to Penicillium infestation were initially screened (Cs_ont_3g000400, Cs_ont_3g003210, Cs_ont_5g007090, Cs_ont_5g011180, Cs_ont_8g020880). This study provides some theoretical basis for subsequent research into the response mechanism of sweet orange bZIP transcription factors under biotic stresses.

Genome-wide identification, characterization, and expression profile of NBS-LRR gene family in sweet orange (Citrus sinensis)

BackgroundThe NBS-LRR (nucleotide-binding site-leucine-rich repeat gene) gene family, known as the plant R (resistance) gene family with the most members, plays a significant role in plant resistance to various external adversity stresses. The NBS-LRR gene family has been researched in many plant species. Citrus is one of the most vital global cash crops, the number one fruit group, and the third most traded agricultural product world wild. However, as one of the largest citrus species, a comprehensive study of the NBS-LRR gene family has not been reported on sweet oranges. MethodsIn this study, NBS-LRR genes were identified from the Citrus sinensis genome (v3.0), with a comprehensive analysis of this gene family performed, including phylogenetic analysis, gene structure, cis-acting element of a promoter, and chromosomal localization, among others. The expression pattern of NBS-LRR genes was analyzed when sweet orange fruits were infected by Penicillium digitatum, employing experimental data from our research group. It first reported the expression patterns of NBS-LRR genes under abiotic stresses, using three transcript data from NCBI (National Center for Biotechnology Information). ResultsIn this study, 111 NBS-LRR genes were identified in the C. sinensis genome (v3.0) and classified into seven subfamilies according to their N-terminal and C-terminal domains. The phylogenetic tree results indicate that genes containing only the NBS structural domain are more ancient in the sweet orange NBS-LRR gene family. The chromosome localization results showed that 111 NBS-LRR genes were distributed unevenly on nine chromosomes, with the most genes distributed on chromosome 1. In addition, we identified a total of 18 tandem duplication gene pairs in the sweet orange NBS-LRR gene family, and based on the Ka/Ks ratio, all of the tandem duplication genes underwent purifying selection. Transcriptome data analysis showed a significant number of NBS-LRR genes expressed under biotic and abiotic stresses, and some reached significantly different levels of expression. It indicates that the NBS-LRR gene family is vital in resistance to biotic and abiotic stresses in sweet oranges. ConclusionOur study provides the first comprehensive framework on the NBS-LRR family of genes, which provides a basis for further in-depth studies on the biological functions of NBS-LRR in growth, development, and response to abiotic stresses in sweet orange.

Comparison of SWEET gene family between maize and foxtail millet through genomic, transcriptomic, and proteomic analyses.

Foxtail millet [Setaria italica (L.) P. Beauv.] does not show high yield and biomass compared with maize (Zea mays L.) although it is a C4 crop with the potential for high productivity. Because SWEET genes, which are important for sugar transport in plants, play critical roles in biomass production and seed filling in crops, genome-wide, transcriptomic, and proteomic comparison on SWEET gene family between these two species would provide some clues for unlocking this issue. In our study, 24 SWEET genes were identified in foxtail millet and maize. Sequence-based bioinformatics combined with gene expression analyses identified several candidate functional orthologs in these two species. A comparative analysis on expression characteristics of SWEET genes and proteins between maize and foxtail millet indicate that not only some critical major SWEET proteins show significant upregulation in maize compared with their orthologs in foxtail millet, but also there are more quantities of maize SWEET genes showing high expressions than that of foxtail millet genes, suggesting that compared with foxtail millet, maize possesses higher capacity of sugar transport, the crucial determinant for crop yield and biomass. These results provide a basis on revealing why foxtail millet exhibits low yield and biomass although it is a C4 crop with the potential for high productivity.

Improved bacterial leaf blight disease resistance in the major elite Vietnamese rice cultivar TBR225 via editing of the OsSWEET14 promoter.

TBR225 is one of the most popular commercial rice varieties in Northern Vietnam. However, this variety is highly susceptible to bacterial leaf blight (BLB), a disease caused by Xanthomonas oryzae pv. oryzae (Xoo) which can lead to important yield losses. OsSWEET14 belongs to the SWEET gene family that encodes sugar transporters. Together with other Clade III members, it behaves as a susceptibility (S) gene whose induction by Asian Xoo Transcription-Activator-Like Effectors (TALEs) is absolutely necessary for disease. In this study, we sought to introduce BLB resistance in the TBR225 elite variety. First, two Vietnamese Xoo strains were shown to up-regulate OsSWEET14 upon TBR225 infection. To investigate if this induction is connected with disease susceptibility, nine TBR225 mutant lines with mutations in the AvrXa7, PthXo3 or TalF TALEs DNA target sequences of the OsSWEET14 promoter were obtained using the CRISPR/Cas9 editing system. Genotyping analysis of T0 and T1 individuals showed that mutations were stably inherited. None of the examined agronomic traits of three transgene-free T2 edited lines were significantly different from those of wild-type TBR225. Importantly, one of these T2 lines, harboring the largest homozygous 6-bp deletion, displayed decreased OsSWEET14 expression as well as a significantly reduced susceptibility to a Vietnamese Xoo strains and complete resistance to another one. Our findings indicate that CRISPR/Cas9 editing conferred an improved BLB resistance to a Vietnamese commercial elite rice variety.

Genome-wide identification and expression analysis of bHLH transcription factor family in response to cold stress in sweet cherry (Prunus avium L.)

The basic helix-loop-helix (bHLH) family is one of the largest families of transcription factors (TFs) in plants and plays crucial roles in regulating growth, development and abiotic stress responses. However, systematic analyses of the bHLH TF family in sweet cherry (Prunus avium L.) have not been reported to date. In our study, 66 bHLH genes were identified in the sweet cherry genome, and the result of phylogenetic analysis indicated that these PavbHLHs could be classified into 17 subfamilies according to the classification of bHLHs in Arabidopsis thaliana. Sixty PavbHLH genes were unevenly distributed on 8 chromosomes, and 6 PavbHLH genes could not be mapped to any chromosome. Based on the PavbHLH’s amino acid sequences, 10 motifs were identified. Motif 1 and motif 2 were highly conserved among the almost all PavbHLH proteins. Exon-intron analysis indicated that proteins belonging to same subfamily exhibited a similar gene structure. Furthermore, promoter cis-element and protein interaction network prediction analysis suggested that most members of the PavbHLH family are involved in various processes in responses to cold stress. The results of semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) showed that 62 PavbHLH genes were all expressed to varying degrees during various low-temperature treatments, of which the expression levels of approximately 20 PavbHLHs were rapidly induced in the early stages of 4 and 10 °C treatment, reached a peak and decreasing thereafter, while the expression continued to be upregulated at 16 °C. Combined with the results of the quantitative real-time PCR (qRT-PCR), it was preliminarily determined that PavbHLH1, -18, -28, -60, -61, -65 and -66 may be involved in regulating the responses to cold stress in sweet cherry. The present study offers useful perception into the sweet cherry bHLH gene family and its responses in cold stress.

Genome-wide identification and expression analysis of SWEET gene family in Litchi chinensis reveal the involvement of LcSWEET2a/3b in early seed development

BackgroundSWEETs (Sugar Will Eventually be Exported transporters) function as sugar efflux transporters that perform diverse physiological functions, including phloem loading, nectar secretion, seed filling, and pathogen nutrition. The SWEET gene family has been identified and characterized in a number of plant species, but little is known about in Litchi chinensis, which is an important evergreen fruit crop.ResultsIn this study, 16 LcSWEET genes were identified and nominated according to its homologous genes in Arabidopsis and grapevine. Multiple sequence alignment showed that the 7 alpha-helical transmembrane domains (7-TMs) were basically conserved in LcSWEETs. The LcSWEETs were divided into four clades (Clade I to Clade IV) by phylogenetic tree analysis. A total of 8 predicted motifs were detected in the litchi LcSWEET genes. The 16 LcSWEET genes were unevenly distributed in 9 chromosomes and there was one pairs of segmental duplicated events by synteny analysis. The expression patterns of the 16 LcSWEET genes showed higher expression levels in reproductive organs. The temporal and spatial expression patterns of LcSWEET2a and LcSWEET3b indicated they play central roles during early seed development.ConclusionsThe litchi genome contained 16 SWEET genes, and most of the genes were expressed in different tissues. Gene expression suggested that LcSWEETs played important roles in the growth and development of litchi fruits. Genes that regulate early seed development were preliminarily identified. This work provides a comprehensive understanding of the SWEET gene family in litchi, laying a strong foundation for further functional studies of LcSWEET genes and improvement of litchi fruits.