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

Genome-wide analysis of the common bean (Phaseolus vulgaris) laccase gene family and its functions in response to abiotic stress

BACKGROUND

Laccase (LAC) gene family plays a pivotal role in plant lignin biosynthesis and adaptation to various stresses. Limited research has been conducted on laccase genes in common beans.

RESULTS

29 LAC gene family members were identified within the common bean genome, distributed unevenly in 9 chromosomes. These members were divided into 6 distinct subclades by phylogenetic analysis. Further phylogenetic analyses and synteny analyses indicated that considerable gene duplication and loss presented throughout the evolution of the laccase gene family. Purified selection was shown to be the major evolutionary force through Ka / Ks. Transcriptional changes of PvLAC genes under low temperature and salt stress were observed, emphasizing the regulatory function of these genes in such conditions. Regulation by abscisic acid and gibberellins appears to be the case for PvLAC3, PvLAC4, PvLAC7, PvLAC13, PvLAC14, PvLAC18, PvLAC23, and PvLAC26, as indicated by hormone induction experiments. Additionally, the regulation of PvLAC3, PvLAC4, PvLAC7, and PvLAC14 in response to nicosulfuron and low-temperature stress were identified by virus-induced gene silence, which demonstrated inhibition on growth and development in common beans.

CONCLUSIONS

The research provides valuable genetic resources for improving the resistance of common beans to abiotic stresses and enhance the understanding of the functional roles of the LAC gene family.

The Analysis, Description, and Examination of the Maize LAC Gene Family's Reaction to Abiotic and Biotic Stress

Laccase (LAC) is a diverse group of genes found throughout the plant genome essential for plant growth and the response to stress by converting monolignin into intricate lignin formations. However, a comprehensive investigation of maize laccase has not yet been documented. A bioinformatics approach was utilized in this research to conduct a thorough examination of maize (Zea mays L.), resulting in the identification and categorization of 22 laccase genes (ZmLAC) into six subfamilies. The gene structure and motifs of each subgroup were largely consistent. The distribution of the 22 LAC genes was uneven among the maize chromosomes, with the exception of chromosome 9. The differentiation of the genes was based on fragment replication, and the differentiation time was about 33.37 million years ago. ZmLAC proteins are primarily acidic proteins. There are 18 cis-acting elements in the promoter sequences of the maize LAC gene family associated with growth and development, stress, hormones, light response, and stress response. The analysis of tissue-specific expression revealed a high expression of the maize LAC gene family prior to the V9 stage, with minimal expression at post-V9. Upon reviewing the RNA-seq information from the publicly available transcriptome, it was discovered that ZmLAC5, ZmLAC10, and ZmLAC17 exhibited significant expression levels when exposed to various biotic and abiotic stress factors, suggesting their crucial involvement in stress responses and potential value for further research. This study offers an understanding of the functions of the LAC genes in maize's response to biotic and abiotic stress, along with a theoretical basis for comprehending the molecular processes at play.

Grass lignin: biosynthesis, biological roles, and industrial applications

Lignin is a phenolic heteropolymer found in most terrestrial plants that contributes an essential role in plant growth, abiotic stress tolerance, and biotic stress resistance. Recent research in grass lignin biosynthesis has found differences compared to dicots such as Arabidopsis thaliana. For example, the prolific incorporation of hydroxycinnamic acids into grass secondary cell walls improve the structural integrity of vascular and structural elements via covalent crosslinking. Conversely, fundamental monolignol chemistry conserves the mechanisms of monolignol translocation and polymerization across the plant phylum. Emerging evidence suggests grass lignin compositions contribute to abiotic stress tolerance, and periods of biotic stress often alter cereal lignin compositions to hinder pathogenesis. This same recalcitrance also inhibits industrial valorization of plant biomass, making lignin alterations and reductions a prolific field of research. This review presents an update of grass lignin biosynthesis, translocation, and polymerization, highlights how lignified grass cell walls contribute to plant development and stress responses, and briefly addresses genetic engineering strategies that may benefit industrial applications.

Impact of bioenergy feedstock carbon farming on sustainable aviation fuel viability in the United States

Biomass-derived sustainable aviation fuel holds significant potential for decarbonizing the aviation sector. Its long-term viability depends on crop choice, longevity of soil organic carbon (SOC) sequestration, and the biomass-to-biojet fuel conversion efficiency. We explored the impact of fuel price and SOC value on viable biojet fuel production scale by integrating an agroecosystem model with a field-to-biojet fuel production process model for 1,4-dimethylcyclooctane (DMCO), a representative high-performance biojet fuel molecule, from Miscanthus, sorghum, and switchgrass. Assigning monetary value to SOC sequestration results in substantially different outcomes than an increased fuel selling price. If SOC accumulation is valued at $185/ton CO2, planting Miscanthus for conversion to DMCO would be economically cost-competitive across 66% of croplands across the continental United States (US) by 2050 if conventional jet fuel remains at $0.74/L (in 2020 US dollars). Cutting the SOC sequestration value in half reduces the viable area to 54% of cropland, and eliminating any payment for SOC shrinks the viable area to 16%. If future biojet fuel prices increase to $1.24/L-Jet A-equivalent, 48 to 58% of the total cultivated land in the United States could support a more diverse set of feedstocks including Miscanthus, sorghum, or switchgrass. Among these options, only 8-14% of the area would be suitable exclusively for Miscanthus cultivation. These findings highlight the intersection of natural solutions for carbon removal and the use of deep-rooted feedstocks for biofuels and biomanufacturing. The results underscore the need to establish clear and consistent values for SOC sequestration to enable the future bioeconomy.

Genome-wide analysis of the laccase (LAC) gene family in Aeluropus littoralis: A focus on identification, evolution and expression patterns in response to abiotic stresses and ABA treatment

Laccases are plant enzymes with essential functions during growth and development. These monophenoloxidases are involved in lignin polymerization, and their expression respond to environmental stress. However, studies of laccases in some plants and fungi have highlighted that many structural and functional aspects of these genes are still unknown. Here, the laccase gene family in Aeluropus littoralis (AlLAC) is described based on sequence structure and expression patterns under abiotic stresses and ABA treatment. Fifteen non-redundant AlLACs were identified from the A. littoralis genome, which showed differences in physicochemical characteristics and gene structure. Based on phylogenetic analysis, AlLACs and their orthologues were classified into five groups. A close evolutionary relationship was observed between LAC gene family members in rice and A. littoralis. According to the interaction network, AlLACs interact more with proteins involved in biological processes such as iron incorporation into the metallo-sulfur cluster, lignin catabolism, regulation of the symbiotic process and plant-type primary cell wall biogenesis. Gene expression analysis of selected AlLACs using real-time RT (reverse transcription)-PCR revealed that AlLACs are induced in response to abiotic stresses such as cold, salt, and osmotic stress, as well as ABA treatment. Moreover, AlLACs showed differential expression patterns in shoot and root tissues. Our findings indicate that AlLACs are preferentially involved in the late response of A. littoralis to abiotic stress.

Genome-wide analysis of the laccase gene family in wheat and relationship with arbuscular mycorrhizal colonization

We identified 156 laccase genes belonging to 11 subfamilies in the wheat genome, and the natural variation of laccase genes significantly affected the development of wheat-arbuscular mycorrhizal symbiosis. Laccases (LACs) have a variety of functions in plant lignification, cell elongation and stress responses. This study aimed to reveal the phylogeny, chromosomal spatial distribution, coexpression and evolution of LAC genes in the wheat genome and to investigate the possible roles of LAC genes during arbuscular mycorrhizal (AM) symbiosis. The genomic characteristics of LAC genes were analyzed by using bioinformatics analysis methods, and the polymorphisms of LAC genes were analyzed by using a diverse wheat panel composed of 289 wheat cultivars. We identified 156 LAC genes belonging to 11 subfamilies in the wheat genome, and segmental duplication dominated the amplification of the LAC gene family in the wheat genome. LACs are dominantly located in the R2 region of wheat chromosomes. Some LACs are collinear with the characterized LACs in Arabidopsis thaliana or rice. A number of genes encoding transcription factors, kinases, and phosphatases were coexpressed with LAC genes in wheat. TaLACs may be potential targets for some miRNAs. Most TaLACs are mainly expressed in the roots and stems of plants. The expression of TaLACs could be regulated by the inoculation of Fusarium graminearum or AM fungi. The polymorphisms of TaLACs mainly accumulate by random drift instead of by selection. Through candidate gene association analysis, we found that the natural variations in TaLACs significantly affected root colonization by AM fungi. The present study provides useful information for further study of the biological functions of LAC genes in wheat, especially the roles of LAC genes during the development of AM symbiosis.

RNA-Seq and Genome-Wide Association Studies Reveal Potential Genes for Rice Seed Shattering

The loss of the shattering ability is one of the key events in rice domestication. The strength of the seed shattering ability is closely related to the harvest yield and the adaptability of modern mechanical harvesting methods. In this study, using a population of 587 natural rice cultivars, quantitative trait loci associated with seed shattering were detected by genome-wide association studies (GWASs). We consider the quantitative trait loci (QTLs) qBTS1 and qBTS3 to be the key loci for seed shattering in rice. Additionally, the abscission zone (AZ) and nonabscission zone (NAZ) of materials with a loss of shattering (DZ129) and easy shattering (W517) were subjected to RNA-Seq, and high-quality differential expression profiles were obtained. The AZ-specific differentially expressed genes (DEGs) of W517 were significantly enriched in plant hormone signal transduction, while the AZ-specific DEGs of DZ129 were enriched in phenylpropanoid biosynthesis. We identified candidate genes for the lignin-associated laccase precursor protein (LOC_Os01g63180) and the glycoside hydrolase family (LOC_Os03g14210) in the QTLs qBTS1 (chromosome 1) and qBTS3 (chromosome 3), respectively. In summary, our findings lay the foundation for the further cloning of qBTS1 and qBTS3, which would provide new insights into seed shattering in rice.

Genome-Wide Identification of Switchgrass Laccases Involved in Lignin Biosynthesis and Heavy-Metal Responses

Plant laccase genes belong to a multigene family, play key roles in lignin polymerization, and participate in the resistance of plants to biotic and abiotic stresses. Switchgrass is an important resource for forage and bioenergy production, yet information about the switchgrass laccase gene family is scarce. Using bioinformatic approaches, a genome-wide analysis of the laccase multigene family in switchgrass was carried out in this study. In total, 49 laccase genes (PvLac1 to PvLac49) were identified; these can be divided into five subclades, and 20 of them were identified as targets of miR397. The tandem and segmental duplication of laccase genes on Chr05 and Chr08 contributed to the expansion of the laccase family. The laccase proteins shared conserved signature sequences but displayed relatively low sequence similarity, indicating the potential functional diversity of switchgrass laccases. Switchgrass laccases exhibited distinct tissue/organ expression patterns, revealing that some laccases might be involved in the lignification process during stem development. All five of the laccase isoforms selected from different subclades responded to heavy metal. The immediate response of lignin-related laccases, as well as the delayed response of low-abundance laccases, to heavy-metal treatment shed light on the multiple roles of laccase isoforms in response to heavy-metal stress.

Genome-wide identification and characterization of laccase family members in eggplant (Solanum melongena L.)

Laccase, as a copper-containing polyphenol oxidase, primarily functions in the process of lignin, anthocyanin biosynthesis, and various abiotic/biotic stresses. In this study, forty-eight laccase members were identified in the eggplant genome. Only forty-two laccase genes from eggplant (SmLACs) were anchored unevenly in 12 chromosomes, the other six SmLACs were mapped on unanchored scaffolds. Phylogenetic analysis indicated that only twenty-five SmLACs were divided into six different groups on the basis of groups reported in Arabidopsis. Gene structure analysis revealed that the number of exons ranged from one to 13. Motif analysis revealed that SmLACs included six conserved motifs. In aspects of gene duplication analysis, twenty-one SmLACs were collinear with LAC genes from Arabidopsis, tomato or rice. Cis-regulatory elements analysis indicated many SmLACs may be involved in eggplant morphogenesis, flavonoid biosynthesis, diverse stresses and growth/development processes. Expression analysis further confirmed that a few SmLACs may function in vegetative and reproductive organs at different developmental stages and also in response to one or multiple stresses. This study would help to further understand and enrich the physiological function of the SmLAC gene family in eggplant, and may provide high-quality genetic resources for eggplant genetics and breeding.

Genetic Dissection and Quantitative Trait Loci Mapping of Agronomic and Fodder Quality Traits in Sorghum Under Different Water Regimes

Livestock provides an additional source of income for marginal cropping farmers, but crop residues that are used as a main source of animal feed are characteristically low in digestibility and protein content. This reduces the potential livestock product yield and quality. The key trait, which influences the quality and the cost of animal feed, is digestibility. In this study, we demonstrate that sorghum breeding can be directed to achieve genetic gains for both fodder biomass and digestibility without any trade-offs. The genotypic variance has shown significant differences for biomass across years (13,035 in 2016 and 3,395 in 2017) while in vitro organic matter digestibility (IVOMD) showed significant genotypic variation in 2016 (0.253) under drought. A range of agronomic and fodder quality traits was found to vary significantly in the population within both the control and drought conditions and across both years of the study. There was significant genotypic variance (σg2) and genotypic × treatment variance (σgxt2) in dry matter production in a recombinant inbred line (RIL) population in both study years, while there was only significant σg2 and σgxt2 in IVOMD under the control conditions. There was no significant correlation identified between biomass and digestibility traits under the control conditions, but there was a positive correlation under drought. However, a negative relation was observed between digestibility and grain yield under the control conditions, while there was no significant correlation under drought population, which was genotyped using the genotyping-by-sequencing (GBS) technique, and 1,141 informative single nucleotide polymorphism (SNP) markers were identified. A linkage map was constructed, and a total of 294 quantitative trait loci (QTLs) were detected, with 534 epistatic interactions, across all of the traits under study. QTL for the agronomic traits fresh and dry weight, together with plant height, mapped on to the linkage group (LG) 7, while QTL for IVOMD mapped on to LG1, 2, and 8. A number of genes previously reported to play a role in nitrogen metabolism and cell wall-related functions were found to be associated with these QTL.

The Laccase Gene Family Mediate Multi-Perspective Trade-Offs during Tea Plant (Camellia sinensis) Development and Defense Processes

Laccase (LAC) plays important roles in different plant development and defense processes. In this study, we identified laccase genes (CsLACs) in Camellia sinensis cv ‘Longjing43′ cultivars, which were classified into six subclades. The expression patterns of CsLACs displayed significant spatiotemporal variations across different tissues and developmental stages. Most members in subclades II, IV and subclade I exhibited contrasting expression patterns during leaf development, consistent with a trade-off model for preferential expression in the early and late developmental stages. The extensive transcriptional changes of CsLACs under different phytohormone and herbivore treatment were observed and compared, with the expression of most genes in subclades I, II and III being downregulated but genes in subclades IV, V and VI being upregulated, suggesting a growth and defense trade-off model between these subclades. Taken together, our research reveal that CsLACs mediate multi-perspective trade-offs during tea plant development and defense processes and are involved in herbivore resistance in tea plants. More in-depth research of CsLACs upstream regulation and downstream targets mediating herbivore defense should be conducted in the future.

Insights into salvianolic acid B biosynthesis from chromosome-scale assembly of the Salvia bowleyana genome

Salvia bowleyana is a traditional Chinese medicinal plant that is a source of nutritional supplements rich in salvianolic acid B and a potential experimental system for the exploration of salvianolic acid B biosynthesis in the Labiatae. Here, we report a high-quality chromosome-scale genome assembly of S. bowleyana covering 462.44 Mb, with a scaffold N50 value of 57.96 Mb and 44,044 annotated protein-coding genes. Evolutionary analysis revealed an estimated divergence time between S. bowleyana and its close relative S. miltiorrhiza of ~3.94 million years. We also observed evidence of a whole-genome duplication in the S. bowleyana genome. Transcriptome analysis showed that SbPAL1 (PHENYLALANINE AMMONIA-LYASE1) is highly expressed in roots relative to stem and leaves, paralleling the location of salvianolic acid B accumulation. The laccase gene family in S. bowleyana outnumbered their counterparts in both S. miltiorrhiza and Arabidopsis thaliana, suggesting that the gene family has undergone expansion in S. bowleyana. Several laccase genes were also highly expressed in roots, where their encoded proteins may catalyze the oxidative reaction from rosmarinic acid to salvianolic acid B. These findings provide an invaluable genomic resource for understanding salvianolic acid B biosynthesis and its regulation, and will be useful for exploring the evolution of the Labiatae.

Large-scale genome-wide association study reveals that drought-induced lodging in grain sorghum is associated with plant height and traits linked to carbon remobilisation

KEY MESSAGE

We detected 213 lodging QTLs and demonstrated that drought-induced stem lodging in grain sorghum is substantially associated with stay-green and plant height suggesting a critical role of carbon remobilisation. Sorghum is generally grown in water limited conditions and often lodges under post-anthesis drought, which reduces yield and quality. Due to its complexity, our understanding on the genetic control of lodging is very limited. We dissected the genetic architecture of lodging in grain sorghum through genome-wide association study (GWAS) on 2308 unique hybrids grown in 17 Australian sorghum trials over 3 years. The GWAS detected 213 QTLs, the majority of which showed a significant association with leaf senescence and plant height (72% and 71%, respectively). Only 16 lodging QTLs were not associated with either leaf senescence or plant height. The high incidence of multi-trait association for the lodging QTLs indicates that lodging in grain sorghum is mainly associated with plant height and traits linked to carbohydrate remobilisation. This result supported the selection for stay-green (delayed leaf senescence) to reduce lodging susceptibility, rather than selection for short stature and lodging resistance per se, which likely reduces yield. Additionally, our data suggested a protective effect of stay-green on weakening the association between lodging susceptibility and plant height. Our study also showed that lodging resistance might be improved by selection for stem composition but was unlikely to be improved by selection for classical resistance to stalk rots.

Molecular Manipulation of MicroRNA397 Abundance Influences the Development and Salt Stress Response of Arabidopsis thaliana

Arabidopsis thaliana (Arabidopsis) has been used extensively as a heterologous system for molecular manipulation to genetically characterize both dicotyledonous and monocotyledonous plant species. Here, we report on Arabidopsis transformant lines molecularly manipulated to over-accumulate the small regulatory RNA microRNA397 (miR397) from the emerging C4 monocotyledonous grass model species Setaria viridis (S. viridis). The generated transformant lines, termed SvMIR397 plants, displayed a range of developmental phenotypes that ranged from a mild, wild-type-like phenotype, to a severe, full dwarfism phenotype. Reverse transcriptase quantitative polymerase chain reaction (RT-qPCR)-based profiling of the SvMIR397 transformant population revealed a strong correlation between the degree of miR397 over-accumulation, repressed LACCASE (LAC) target gene expression, reduced lignin content, and the severity of the developmental phenotype displayed by SvMIR397 transformants. Further, exposure of SvMIR397 transformants to a 7-day regime of salt stress revealed the SvMIR397 transformant lines to be more sensitive to the imposed stress than were wild-type Arabidopsis plants. Taken together, the findings reported here via the use of Arabidopsis as a heterologous system show that the S. viridis miR397 small regulatory RNA is able to repress the expression of three Arabidopsis LAC genes which led to reduced lignin content and increased salt stress sensitivity.

Genome-wide analysis of laccase genes in moso bamboo highlights PeLAC10 involved in lignin biosynthesis and in response to abiotic stresses

Twenty-three PeLACs have been identified in moso bamboo, overexpression of PeLAC10 increases the lignin content and confers drought and phenolic acid tolerance in transgenic Arabidopsis. Laccases (LACs) have multifunction involved in the processes of cell elongation, lignification and stress response in plants. However, the function of laccases in bamboo remain unclear. Here, a total of 23 laccase genes (PeLAC1-PeLAC23) were identified in moso bamboo (Phyllostachys edulis). The diverse gene structure and expression pattern of PeLACs suggested that their function should be spatiotemporal and complicated, which was supported by the expression profiles in different tissues of moso bamboo. Eighteen PeLACs were identified as the targets of ped-miR397. The putative ped-miR397-binding site in the coding region of PeLAC10 was further confirmed by RLM-5' RACE, indicating that PeLAC10 was regulated by ped-miR397 after transcription. With the increasing shoot height, the expression abundance of PeLAC10 was up-regulated and reached the maximum in 15 cm shoots, while that of ped-miR397 was relative lower and showed the minimum in 15 cm shoots. PeLAC10 was up-regulated obviously under both ABA (100 μmol L^-1) and NaCl (400 mmol L^-1) treatments, and it was down-regulated under the GA₃ (100 μmol L^-1) treatment. The transgenic Arabidopsis plants over-expressing PeLAC10 became slightly smaller and their petioles were shorter than those of Col-0. However, they had a stronger capacity in resistance to phenolic acids and drought besides higher lignin content in stems. These results indicated that overexpression of PeLAC10 was helpful to increase the content of lignin in transgenic Arabidopsis and improve the adaptability to phenolic acid and drought stresses.

Genome-wide characterization of the laccase gene family in Setaria viridis reveals members potentially involved in lignification

Five laccase genes are potentially involved in developmental lignification in the model C4 grass Setaria viridis and their different tissue specificities suggest subfunctionalization events. Plant laccases are copper-containing glycoproteins involved in monolignol oxidation and, therefore, their activity is essential for lignin polymerization. Although these enzymes belong to large multigene families with highly redundant members, not all of them are thought to be involved in lignin metabolism. Here, we report on the genome-wide characterization of the laccase gene family in the model C4 grass Setaria viridis and further identification of the members potentially involved in monolignol oxidation. A total of 52 genes encoding laccases (SvLAC1 to SvLAC52) were found in the genome of S. viridis, and phylogenetic analyses showed that these genes were heterogeneously distributed among the characteristic six subclades of the family and are under relaxed selective constraints. The observed expansion in the total number of genes in this species was mainly caused by tandem duplications within subclade V, which accounts for 68% of the whole family. Comparative phylogenetic analyses showed that the expansion of subclade V is specifically observed for the Paniceae tribe within the Panicoideae subfamily in grasses. Five SvLAC genes (SvLAC9, SvLAC13, SvLAC15, SvLAC50, and SvLAC52) fulfilled the criteria established to identify lignin-related candidates: (1) phylogenetic proximity to previously characterized lignin-related laccases from other species, (2) similar expression pattern to that observed for lignin biosynthetic genes in the S. viridis elongating internode, and (3) high expression in S. viridis tissues undergoing active lignification. In addition, in situ hybridization experiments not only confirmed that these selected SvLAC genes were expressed in lignifying cells, but also that their expression showed different tissue specificities, suggesting subfunctionalization events within the family. These five laccase genes are strong candidates to be involved in lignin polymerization in S. viridis and might be good targets for lignin bioengineering strategies.

The Soybean Laccase Gene Family: Evolution and Possible Roles in Plant Defense and Stem Strength Selection

Laccase is a widely used industrial oxidase for food processing, dye synthesis, paper making, and pollution remediation. At present, laccases used by industries come mainly from fungi. Plants contain numerous genes encoding laccase enzymes that show properties which are distinct from that of the fungal laccases. These plant-specific laccases may have better potential for industrial purposes. The aim of this work was to conduct a genome-wide search for the soybean laccase genes and analyze their characteristics and specific functions. A total of 93 putative laccase genes (GmLac) were identified from the soybean genome. All 93 GmLac enzymes contain three typical Cu-oxidase domains, and they were classified into five groups based on phylogenetic analysis. Although adjacent members on the tree showed highly similar exon/intron organization and motif composition, there were differences among the members within a class for both conserved and differentiated functions. Based on the expression patterns, some members of laccase were expressed in specific tissues/organs, while some exhibited a constitutive expression pattern. Analysis of the transcriptome revealed that some laccase genes might be involved in providing resistance to oomycetes. Analysis of the selective pressures acting on the laccase gene family in the process of soybean domestication revealed that 10 genes could have been under artificial selection during the domestication process. Four of these genes may have contributed to the transition of the soft and thin stem of wild soybean species into strong, thick, and erect stems of the cultivated soybean species. Our study provides a foundation for future functional studies of the soybean laccase gene family.

Genome-Wide Identification of the LAC Gene Family and Its Expression Analysis Under Stress in Brassica napus

Lignin is an important biological polymer in plants that is necessary for plant secondary cell wall ontogenesis. The laccase (LAC) gene family catalyzes lignification and has been suggested to play a vital role in the plant kingdom. In this study, we identified 45 LAC genes from the Brassica napus genome (BnLACs), 25 LAC genes from the Brassica rapa genome (BrLACs) and 8 LAC genes from the Brassica oleracea genome (BoLACs). These LAC genes could be divided into five groups in a cladogram and members in same group had similar structures and conserved motifs. All BnLACs contained hormone- and stress- related elements determined by cis-element analysis. The expression of BnLACs was relatively higher in the root, seed coat and stem than in other tissues. Furthermore, BnLAC4 and its predicted downstream genes showed earlier expression in the silique pericarps of short silique lines than long silique lines. Three miRNAs (miR397a, miR397b and miR6034) target 11 BnLACs were also predicted. The expression changes of BnLACs under series of stresses were further investigated by RNA sequencing (RNA-seq) and quantitative real-time polymerase chain reaction (qRT-PCR). The study will give a deeper understanding of the LAC gene family evolution and functions in B. napus.

Inactivation of LACCASE8 and LACCASE5 genes in Brachypodium distachyon leads to severe decrease in lignin content and high increase in saccharification yield without impacting plant integrity

BACKGROUND

Dedicated lignocellulosic feedstock from grass crops for biofuel production is extensively increasing. However, the access to fermentable cell wall sugars by carbohydrate degrading enzymes is impeded by lignins. These complex polymers are made from reactive oxidized monolignols in the cell wall. Little is known about the laccase-mediated oxidation of monolignols in grasses, and inactivation of the monolignol polymerization mechanism might be a strategy to increase the yield of fermentable sugars.

RESULTS

LACCASE5 and LACCASE8 are inactivated in a Brachypodium double mutant. Relative to the wild type, the lignin content of extract-free mature culms is decreased by 20-30% and the saccharification yield is increased by 140%. Release of ferulic acid by mild alkaline hydrolysis is also 2.5-fold higher. Interfascicular fibers are mainly affected while integrity of vascular bundles is not impaired. Interestingly, there is no drastic impact of the double mutation on plant growth.

CONCLUSION

This work shows that two Brachypodium laccases with clearly identified orthologs in crops are involved in lignification of this model plant. Lignification in interfascicular fibers and metaxylem cells is partly uncoupled in Brachypodium. Orthologs of these laccases are promising targets for improving grass feedstock for cellulosic biofuel production.

Plant Responses to Pathogen Attack: Small RNAs in Focus

Small RNAs (sRNA) are a significant group of gene expression regulators for multiple biological processes in eukaryotes. In plants, many sRNA silencing pathways produce extensive array of sRNAs with specialized roles. The evidence on record advocates for the functions of sRNAs during plant microbe interactions. Host sRNAs are reckoned as mandatory elements of plant defense. sRNAs involved in plant defense processes via different pathways include both short interfering RNA (siRNA) and microRNA (miRNA) that actively regulate immunity in response to pathogenic attack via tackling pathogen-associated molecular patterns (PAMPs) and other effectors. In response to pathogen attack, plants protect themselves with the help of sRNA-dependent immune systems. That sRNA-mediated plant defense responses play a role during infections is an established fact. However, the regulations of several sRNAs still need extensive research. In this review, we discussed the topical advancements and findings relevant to pathogen attack and plant defense mediated by sRNAs. We attempted to point out diverse sRNAs as key defenders in plant systems. It is hoped that sRNAs would be exploited as a mainstream player to achieve food security by tackling different plant diseases.