Cell size and xylem differentiation regulating genes from Salicornia europaea contribute to plant salt tolerance.

Cell wall is involved in plant growth and plays pivotal roles in plant adaptation to environmental stresses. Cell wall remodelling may be crucial to salt adaptation in the euhalophyte Salicornia europaea. However, the mechanism underlying this process is still unclear. Here, full-length transcriptome indicated cell wall-related genes were comprehensively regulated under salinity. The morphology and cell wall components in S. europaea shoot were largely modified under salinity. Through the weighted gene co-expression network analysis, SeXTH2 encoding xyloglucan endotransglucosylase/hydrolases, and two SeLACs encoding laccases were focused. Meanwhile, SeEXPB was focused according to expansin activity and the expression profiling. Function analysis in Arabidopsis validated the functions of these genes in enhancing salt tolerance. SeXTH2 and SeEXPB overexpression led to larger cells and leaves with hemicellulose and pectin content alteration. SeLAC1 and SeLAC2 overexpression led to more xylem vessels, increased secondary cell wall thickness and lignin content. Notably, SeXTH2 transgenic rice exhibited enhanced salt tolerance and higher grain yield. Altogether, these genes may function in the succulence and lignification process in S. europaea. This work throws light on the regulatory mechanism of cell wall remodelling in S. europaea under salinity and provides potential strategies for improving crop salt tolerance and yields.

SbYS1 and SbWRKY72 regulate Cd tolerance and accumulation in sweet sorghum.

MAIN CONCLUSION: SbYS1 and its upstream transcription factor SbWRKY72 were involved in Cd tolerance and accumulation and are valuable for developing sweet sorghum germplasm with high-Cd tolerance or accumulation ability through genetic manipulation. Cadmium (Cd) is highly toxic and can severely affect human health. Sweet sorghum, as an energy crop, shows great potential in extracting cadmium from Cd-contaminated soils. However, its molecular mechanisms of Cd-tolerance and -accumulation remain largely unknown. Here, we isolated a YSL family gene SbYS1 from the sweet sorghum genotype with high Cd accumulation ability and the expression of SbYS1 in roots was induced by cadmium. GUS staining experiment exhibited that SbYS1 was expressed in the epidermis and parenchyma tissues of roots. Further subcellular localization analysis suggested that SbYS1 was localized in the endoplasmic reticulum and plasma membrane. Yeast transformed with SbYS1 exhibited a sensitive phenotype compared to the control when exposed to Cd-NA (chelates of cadmium and nicotianamine), indicating that SbYS1 may absorb cadmium in the form of Cd-NA. Arabidopsis overexpressing SbYS1 had a longer root length and accumulated less Cd in roots and shoots. SbWRKY72 bound to the promoter of SbYS1 and negatively regulated the expression of SbYS1. Transgenic Arabidopsis of SbWRKY72 showed higher sensitivity to cadmium and increased cadmium accumulation in roots. Our results provide references for improving the phytoremediation efficiency of sweet sorghum by genetic manipulation in the future.

PHT1;5 Repressed by ANT Mediates Pi Acquisition and Distribution under Low Pi and Salinity in Salt Cress.

Salinity and phosphate (Pi) starvation are the most common abiotic stresses that threaten crop productivity. Salt cress (Eutrema salsugineum) displays good tolerance to both salinity and Pi limitation. Previously, we found several Phosphate Transporter (PHT) genes in salt cress upregulated under salinity. Here, EsPHT1;5 induced by both low Pi (LP) and salinity was further characterized. Overexpression of EsPHT1;5 in salt cress enhanced plant tolerance to LP and salinity, while the knock-down lines exhibited growth retardation. The analysis of phosphorus (P) content and shoot/root ratio of total P in EsPHT1;5-overexpressing salt cress seedlings and the knock-down lines as well as arsenate uptake assays suggested the role of EsPHT1;5 in Pi acquisition and root-shoot translocation under Pi limitation. In addition, overexpression of EsPHT1;5 driven by the native promoter in salt cress enhanced Pi mobilization from rosettes to siliques upon a long-term salt treatment. Particularly, the promoter of EsPHT1;5 outperformed that of AtPHT1;5 in driving gene expression under salinity. We further identified a transcription factor EsANT, which negatively regulated EsPHT1;5 expression and plant tolerance to LP and salinity. Taken together, EsPHT1;5 plays an integral role in Pi acquisition and distribution in plant response to LP and salt stress. Further, EsANT may be involved in the cross-talk between Pi starvation and salinity signaling pathways. This work provides further insight into the mechanism underlying high P use efficiency in salt cress in its natural habitat, and evidence for a link between Pi and salt signaling.

Theoretical investigation of the magnetic and optical properties in a transition metal-doped GaTeCl monolayer.

We investigate the structural, magnetic, electronic and optical properties of a transition metal-doped GaTeCl monolayer, denoted as M@GaTeCl (M = V, Cr, Mn, Fe and Co), by using first-principles calculations. It is found that the magnetic ground state can be regulated by different M elements. In the meantime, the electronic structure is different with the doping of different M metal atoms, and thus the optical absorption changes correspondingly. The electronic calculations of M@GaTeCl suggest that V@GaTeCl, Cr@GaTeCl, Mn@GaTeCl and Fe@GaTeCl are semiconductors and the magnetic ground states are G-type antiferromagnetic (AFM), C-type AFM, A-type AFM and C-type AFM order, respectively, while Co@GaTeCl is a metal and the ground state is ferromagnetic (FM) order. The different magnetic ground states are discussed with the Heisenberg model. The rough estimation of the ferroelectric polarization value of M@GaTeCl suggests that M@GaTeCl still exhibits multiferroicity. The electronic structure is explained by the projected density of states, band structure and decomposed charge of the valence band maximum (VBM) and conduction band minimum (CBM). Simultaneously, the absorption coefficient calculations indicate that M@GaTeCl absorption shows anisotropic properties, as the same as in a pure GaTeCl monolayer, there exists enhanced visible light absorption in these M@GaTeCl monolayers relative to the pure GaTeCl one, which can be interpreted by the anisotropic structure and by the peculiar electronic structure. Thus, we found that the magnetic ground state, the electronic structure, and the absorption coefficient of M@GaTeCl can be tuned by doping different transition metal M atoms, and the ferroelectricity is still retained, which makes M@GaTeCl a potential multifunctional material in spintronics and optics.

Comparative analysis of sRNAs, degradome and transcriptomics in sweet sorghum reveals the regulatory roles of miRNAs in Cd accumulation and tolerance.

MAIN CONCLUSION: Key miRNAs including sbi-miR169p/q, sbi-miR171g/j, sbi-miR172a/c/d, sbi-miR172e, sbi-miR319a/b, sbi-miR396a/b, miR408, sbi-miR5384, sbi-miR5565e and nov_23 were identified to function in the regulation of Cd accumulation and tolerance. As an energy plant, sweet sorghum shows great potential in the phytoremediation of Cd-contaminated soils. However, few studies have focused on the regulatory roles of miRNAs and their targets under Cd stress. In this study, comparative analysis of sRNAs, degradome and transcriptomics was conducted in high-Cd accumulation (H18) and low-Cd accumulation (L69) genotypes of sweet sorghum. A total of 38 conserved and 23 novel miRNAs with differential expressions were identified under Cd stress or between H18 and L69, and 114 target genes of 41 miRNAs were validated. Furthermore, 25 miRNA-mRNA pairs exhibited negatively correlated expression profiles and sbi-miR172e together with its target might participate in the distinct Cd tolerance between H18 and L69 as well as sbi-miR172a/c/d. Additionally, two groups of them: miR169p/q-nov_23 and miR408 were focused through the co-expression analysis, which might be involved in Cd uptake and tolerance by regulating their targets associated with transmembrane transportation, cytoskeleton activity, cell wall construction and ROS (reactive oxygen species) homeostasis. Further experiments exhibited that cell wall components of H18 and L69 were different when exposed to cadmium, which might be regulated by miR169p/q, miR171g/j, miR319a/b, miR396a/b, miR5384 and miR5565e through their targets. Through this study, we aim to reveal the potential miRNAs involved in sweet sorghum in response to Cd stress and provide references for developing high-Cd accumulation or high Cd-resistant germplasm of sweet sorghum that can be used in phytoremediation.

Variation of PHT families adapts salt cress to phosphate limitation under salinity.

Salt cress (Eutrema salsugineum) presents relatively high phosphate (Pi) use efficiency cy in its natural habitat. Phosphate Transporters (PHTs) play critical roles in Pi acquisition and homeostasis. Here, a comparative study of PHT families between salt cress and Arabidopsis was performed. A total of 27 putative PHT genes were identified in E. salsugineum genome. Notably, seven tandem genes encoding PHT1;3 were found, and function analysis in Arabidopsis indicated at least six EsPHT1;3s participated in Pi uptake. Meanwhile, different expression profiles of PHT genes between the two species under Pi limitation and salt stress were documented. Most PHT1 genes were down-regulated in Arabidopsis while up-regulated in salt cress under salinity, among which EsPHT1;9 was further characterized. EsPHT1;9 was involved in root-to-shoot Pi translocation. Particularly, the promoter of EsPHT1;9 outperformed that of AtPHT1;9 in promoting Pi translocation, K+ /Na+ ratio, thereby salt tolerance. Through cis-element analysis, we identified a bZIP transcription factor EsABF5 negatively regulating EsPHT1;9 and plant tolerance to low-Pi and salt stress. Altogether, more copies and divergent transcriptional regulation of PHT genes contribute to salt cress adaptation to the co-occurrence of salinity and Pi limitation, which add our knowledge on the evolutionary and molecular component of multistress- tolerance of this species.

Phosphatidylserine Synthase from Salicornia europaea Is Involved in Plant Salt Tolerance by Regulating Plasma Membrane Stability.

Salinity-induced lipid alterations have been reported in many plant species; however, how lipid biosynthesis and metabolism are regulated and how lipids work in plant salt tolerance are much less studied. Here, a constitutively much higher phosphatidylserine (PS) content in the plasma membrane (PM) was found in the euhalophyte Salicornia europaea than in Arabidopsis. A gene encoding PS synthase (PSS) was subsequently isolated from S. europaea, named SePSS, which was induced by salinity. Multiple alignments and phylogenetic analysis suggested that SePSS belongs to a base exchange-type PSS, which localises to the endoplasmic reticulum. Knockdown of SePSS in S. europaea suspension cells resulted in reduced PS content, decreased cell survival rate, and increased PM depolarization and K+ efflux under 400 or 800 mM NaCl. By contrast, the upregulation of SePSS leads to increased PS and phosphatidylethanolamine levels and enhanced salt tolerance in Arabidopsis, along with a lower accumulation of reactive oxygen species, less membrane injury, less PM depolarization and higher K+/Na+ in the transgenic lines than in wild-type (WT). These results suggest a positive correlation between PS levels and plant salt tolerance, and that SePSS participates in plant salt tolerance by regulating PS levels, hence PM potential and permeability, which help maintain ion homeostasis. Our work provides a potential strategy for improving plant growth under multiple stresses.

Comparison of actual and simulated tumoricidal effects induced by photodynamic therapy.

OBJECTIVES: Numerous studies employ mathematical methods, such as Monte Carlo simulation, to predict the tumor killing effects of photodynamic therapy (PDT) by simulating optical propagation, photosensitizer distribution, and oxygen distribution. Whether these models faithfully reflect tumor killing is unknown, and model validation using tumor cross sections in these studies is usually insufficient to answer this question. To fill this gap in our knowledge, we employed a mouse model of breast cancer to determine the spatiotemporal effects of PDT using direct histopathological and biochemical analyses of whole tumors. METHODS: We prepared approximately 700 5-µm-thick serial sections of breast tumors of syngeneic mice treated with PDT employing the photosensitizer photocarcinorin (PsD-007, a second-generation photosensitizer developed in China). Three adjoining sections were subjected to hematoxylin and eosin staining to assess necrosis, the TUNEL assay to evaluate apoptosis, and CD31 staining to detect angiogenesis, respectively. We then generated a three-dimensional (3D) reconstruction of the tumor to evaluate these processes. We simultaneously used the Monte Carlo method to develop a model of light distribution throughout the tumor to evaluate the actual and simulated tumor killing effects induced by PDT. RESULTS: Tumor necrosis decreased exponentially as a function of distance from the source of illumination, while the distributions of apoptosis and neovascularization were independent of light distribution. Most apoptosis occurred in the lower layers (3000-4000 µm) of the tumor where the light intensity was too low to excite the photosensitizer. Neovascularization occurred at depths ranging from 2500 to 3500 µm. These analyses provided a 3D view of how a tumor is destroyed using PDT. CONCLUSIONS: Although the optical distribution model predicted tumor necrosis caused by PDT, it was ineffective in predicting the sites of apoptosis and vascular destruction. Mathematical modeling is limited in its capabilities required to gain a comprehensive understanding of the spatiotemporal events associated with PDT. The mouse model developed here will serve as a platform for detailed direct histopathological, biochemical, and molecular genetic analyses of the effects of PDT, which will facilitate the development of optimized treatment strategies.

Solution-Phase Synthesis of a Base-Free Benzoborirene and a Three-Dimensional Inorganic Analogue.

The base-free benzoborirene 1,2-BR-1,2-C6H4 (7) and its three-dimensional inorganic analogue 1,2-BR-1,2-C2B10H10 (13) have been successfully synthesized by Cp2ZrBr2 and LiCl elimination, respectively. The Cl analogue of the key intermediate for the formation of benzoborirene 7 has been isolated and structurally characterized, thus suggesting the reaction pathway via benzyne Zr complex formation, B-Br/Cbenzyne-Zr σ-bond metathesis, and a Cp2ZrBr2 elimination/ring-closing process. The rationality of the reaction pathway has been confirmed by DFT calculations. In addition, the title compounds shared the same reactivity pattern (i.e., 1,3-silyl migration) toward MeIiPr (8), thus allowing for the synthetic approach to the first carborane-substituted iminoborane 14.

Highlights to phytosterols accumulation and equilibrium in plants: Biosynthetic pathway and feedback regulation.

Phytosterols are a group of sterols exclusive to plants and fungi, but are indispensable to humans because of their medicinal and nutritional values. However, current raw materials used for phytosterols extraction add to the cost and waste in the process. For higher sterols production, major attention is drawn to plant materials abundant in phytosterols and genetic modification. To provide an insight into phytosterols metabolism, the research progress on key enzymes involved in phytosterols biosynthesis and conversions were summarized. CAS, SSR2, SMT, DWF1 and CYP710A, the enzymes participating in the biosynthetic pathway, and PSAT, ASAT and SGT, the enzymes involved in the conversion of free sterols to conjugated ones, were reviewed. Specifically, SMT and CYP710A were emphasized for their function on modulating the percentage composition of different kinds of phytosterols. The thresholds of sterol equilibrium and the resultant phytosterols accumulation, which vary in plant species and contribute to plasma membrane remodeling under stresses, were also discussed. By retrospective analysis of the previous researches, we proposed a feedback mechanism regulating sterol equilibrium underlying sterols metabolism. From a strategic perspective, we regard salt tolerant plant as an alternative to present raw materials, which will attain higher phytosterols production in combination with gene-modification.

[Preface for special issue on bioremediation of contaminated soil (2020)].

As an important strategy for sustainable development, bioremediation technology has been widely used in soil contamination remediation due to the advantages of environmental friendliness, excellent metal removal efficiency and free of secondary pollution. This special issue with a collection of 16 papers covers the research aspects from phytoremediation, microbial repair, combined remediation, molecular mechanisms of heavy metals absorption and accumulation, to beneficial reuse of feedstock resources, presents the recent advances as well as the future prospects involved in bioremediation for soil contamination. We aim to provide useful insights to help future development of bioremediation technology.

[Research progress in phytoremediation of heavy-metal contaminated soils with high-biomass economic plants].

Phytoremediation is one of the important methods for restoring heavy-metal contaminated soils. Using high-biomass economic plants to restore heavy-metal contaminated soils can have both ecological and economic benefits, with great application prospects. Based on the analysis of current situation and existing problems of phytoremediation, we propose the advantages of high-biomass economic plants in contaminated soil remediation, and summarize the recent advances and mechanisms involved in absorbing heavy metals in high-biomass economic plants. Furthermore, the possible methods for improving the remediation efficiency of high-biomass economic plants are also discussed, to provide insights for improving the economic benefits of phytoremediation and promoting its widespread application in the future.

[Application potential of Salicornia europaea in remediation of Cd, Pb and Li contaminated saline soil].

Coastal and inland saline-alkali soil is important reserve land resources. However, some parts of saline land are now under the threat of heavy metals such as cadmium (Cd), lead (Pb) and the light metal lithium (Li). Phytoremediation with halophytes could be the most economical and effective way to restore the contaminated saline soil. In this study, the growth, physiological and biochemical indexes and ion contents of halophyte Salicornia europaea under different concentrations of Cd (0-50 mmol/L), Pb (0-50 mmol/L) and Li (0-400 mmol/L) were investigated to evaluate the tolerance and accumulation of the metal contaminations. The results showed that plant height, fresh weight and dry weight of S. europaea decreased significantly with the increase of Cd and Pb concentration. Low concentration of Li (< 20 mmol/L) promoted the growth of S. europaea, while the growth of plants was inhibited under higher concentration of Li (> 20 mmol/L). The tolerance order of S. europaea to Cd, Pb and Li was Li > Pb > Cd. Cd, Pb and Li stresses may negatively affected Na and K uptake and transport in S. europaea to affect plant growth. In addition, the antioxidant enzyme system synergistically responsed to resist the oxidative toxicity of different ions. The contents of Cd, Pb, Li in roots and shoots of S. europaea also increased with the increase of treatment concentration. Furthermore, Cd and Pb contents in roots were significantly higher than in shoots, while more Li accumulated in shoots than in roots. The aforementioned results showed that S. europaea had strong tolerance along with a high accumulate ability to Cd, Pb and Li, indicating its application potential in restoring Cd, Pb and Li contaminated saline soil. This study laid a basis for further exploration of the tolerance mechanism of S. europaea to Cd, Pb and Li stresses, and gave a new perspective for the usage of S. europaea to remediate Cd, Pb and Li pollutants in high-salinity alkali soils.

Comparative transcriptome combined with morpho-physiological analyses revealed key factors for differential cadmium accumulation in two contrasting sweet sorghum genotypes.

Cadmium (Cd) is a widespread soil contaminant threatening human health. As an ideal energy plant, sweet sorghum (Sorghum bicolor (L.) Moench) has great potential in phytoremediation of Cd-polluted soils, although the molecular mechanisms are largely unknown. In this study, key factors responsible for differential Cd accumulation between two contrasting sweet sorghum genotypes (high-Cd accumulation one H18, and low-Cd accumulation one L69) were investigated. H18 exhibited a much higher ability of Cd uptake and translocation than L69. Furthermore, Cd uptake through symplasmic pathway and Cd concentrations in xylem sap were both higher in H18 than those in L69. Root anatomy observation found the endodermal apoplasmic barriers were much stronger in L69, which may restrict the Cd loading into xylem. The molecular mechanisms underlying these morpho-physiological traits were further dissected by comparative transcriptome analysis. Many genes involved in cell wall modification and heavy metal transport were found to be Cd-responsive DEGs and/or DEGs between these two genotypes. KEGG pathway analysis found phenylpropanoid biosynthesis pathway was over-represented, indicating this pathway may play important roles in differential Cd accumulation between two genotypes. Based on these results, a schematic representation of main processes involved in differential Cd uptake and translocation in H18 and L69 is proposed, which suggests that higher Cd accumulation in H18 depends on a multilevel coordination of efficient Cd uptake and transport, including efficient root uptake and xylem loading, less root cell wall binding, and weaker endodermal apoplasmic barriers.

Identification for the capability of Cd-tolerance, accumulation and translocation of 96 sorghum genotypes.

Cadmium (Cd) pollution is a worldwide environmental problem which heavily threatens human health and food security. Sorghum, as one of the most promising energy crop, has been considered to be the source of high-quality feedstock for ethanol fuel. Ninety-six sorghum genotypes were investigated under hydroponic conditions to compare their capabilities of Cd-tolerance, accumulation and translocation for their potential in remediation of Cd contamination. Different genotypes varied largely in the tolerance to Cd stress with tolerance indexes ranked from 0.107 to 0.933. Great difference was also found in Cd uptake and accumulation with concentrations ranging from 19.0 to 202.4mg/kg in shoots and 277.0-898.3mg/kg in roots. The total amounts of Cd ranked from 6.1 to 25.8µg per plant and the highest translocation factor was over 4 times higher than the lowest one. The correlation analysis demonstrated that Cd concentration in shoot reflected the ability of Cd translocation and tolerance of sorghum, and the path coefficient analysis indicated that root biomass could be taken as a biomarker to evaluate Cd extraction ability of sorghum. The results in this study can facilitate the restoring of Cd contaminated areas by sorghum.

The V-ATPase subunit A is essential for salt tolerance through participating in vacuolar Na+ compartmentalization in Salicornia europaea.

MAIN CONCLUSION: The V-ATPase subunit A participates in vacuolar Na + compartmentalization in Salicornia europaea regulating V-ATPase and V-PPase activities. Na+ sequestration into the vacuole is an efficient strategy in response to salinity in many halophytes. However, it is not yet fully understood how this process is achieved. Particularly, the role of vacuolar H+-ATPase (V-ATPase) in this process is controversial. Our previous proteomic investigation in the euhalophyte Salicornia europaea L. found a significant increase of the abundance of V-ATPase subunit A under salinity. Here, the gene encoding this subunit named SeVHA-A was characterized, and its role in salt tolerance was demonstrated by RNAi directed downregulation in suspension-cultured cells of S. europaea. The transcripts of genes encoding vacuolar H+-PPase (V-PPase) and vacuolar Na+/H+ antiporter (SeNHX1) also decreased significantly in the RNAi cells. Knockdown of SeVHA-A resulted in a reduction in both V-ATPase and vacuolar H+-PPase (V-PPase) activities. Accordingly, the SeVHA-A-RNAi cells showed increased vacuolar pH and decreased cell viability under different NaCl concentrations. Further Na+ staining showed the reduced vacuolar Na+ sequestration in RNAi cells. Taken together, our results evidenced that SeVHA-A participates in vacuolar Na+ sequestration regulating V-ATPase and V-PPase activities and thereby vacuolar pH in S. europaea. The possible mechanisms underlying the reduction of vacuolar V-PPase activity in SeVHA-A-RNAi cells were also discussed.

Roles, Regulation, and Agricultural Application of Plant Phosphate Transporters.

Phosphorus (P) is an essential mineral nutrient for plant growth and development. Low availability of inorganic phosphate (orthophosphate; Pi) in soil seriously restricts the crop production, while excessive fertilization has caused environmental pollution. Pi acquisition and homeostasis depend on transport processes controlled Pi transporters, which are grouped into five families so far: PHT1, PHT2, PHT3, PHT4, and PHT5. This review summarizes the current understanding on plant PHT families, including phylogenetic analysis, function, and regulation. The potential application of Pi transporters and the related regulatory factors for developing genetically modified crops with high phosphorus use efficiency (PUE) are also discussed in this review. At last, we provide some potential strategies for developing high PUE crops under salt or drought stress conditions, which can be valuable for improving crop yields challenged by global scarcity of water resources and increasing soil salinization.

Establishment of a gene function analysis system for the euhalophyte Salicornia europaea L.

KEY MESSAGE: A Salicornia europaea L. in vitro cell transformation system was developed and further applied to SeNHX1 function investigation. The exploration of salt-tolerant genes from halophyte has seriously been limited by the lack of self-dependent transformation system. Here, an Agrobacterium tumefaciens-mediated in vitro cell transformation system of euhalophyte Salicornia europaea L. was developed. Calli derived from hypocotyl of S. europaea were co-cultured for 3 days with Agrobacterium at OD600 ranging from 1.0 to 1.5 and then selected with 25 mg/L hygromycin (Hyg). The transformed cells were identified from Hyg positive calli by GUS assay and qRT-PCR, and the transformation efficiency was up to 74.4%. The practicality of this system was further tested via genetic manipulation of S. europaea Na+/H+ antiporter 1 (SeNHX1) gene by creating the overexpressing, silencing, and empty vector cells. Survival ratio and Na+ distribution under salt treatment showed obvious differences in SeNHX1-overexpressing, -silencing, and empty vector cells, indicating the feasibility of this system to analyze gene function. This investigation is enlightening for studies in other non-model plants lacking of self-dependent transformation system.

Genome-Wide Identification of Sorghum bicolor Laccases Reveals Potential Targets for Lignin Modification.

Laccase is a key enzyme in plant lignin biosynthesis as it catalyzes the final step of monolignols polymerization. Sweet sorghum [Sorghum bicolor (L.) Moench] is considered as an ideal feedstock for ethanol production, but lignin greatly limits the production efficiency. No comprehensive analysis on laccase has ever been conducted in S. bicolor, although it appears as the most promising target for engineering lignocellulosic feedstock. The aim of our work is to systematically characterize S. bicolor laccase gene family and to identify the lignin-specific candidates. A total of twenty-seven laccase candidates (SbLAC1-SbLAC27) were identified in S. bicolor. All SbLACs comprised the equivalent L1-L4 signature sequences and three typical Cu-oxidase domains, but exhibited diverse intron-exon patterns and relatively low sequence identity. They were divided into six groups by phylogenetic clustering, revealing potential distinct functions, while SbLAC5 was considered as the closest lignin-specific candidate. qRT-PCR analysis deciphered that SbLAC genes were expressed preferentially in roots and young internodes of sweet sorghum, and SbLAC5 showed high expression, adding the evidence that SbLAC5 was bona fide involved in lignin biosynthesis. Besides, high abundance of SbLAC6 transcripts was detected, correlating it a potential role in lignin biosynthesis. Diverse cis regulatory elements were recognized in SbLACs promoters, indicating putative interaction with transcription factors. Seven SbLACs were found to be potential targets of sbi-miRNAs. Moreover, putative phosphorylation sites in SbLAC sequences were identified. Our research adds to the knowledge for lignin profile modification in sweet sorghum.