Transcriptome analysis highlights key differentially expressed genes involved in cellulose and lignin biosynthesis of sugarcane genotypes varying in fiber content

GhiPLATZ17 and GhiPLATZ22, zinc-dependent DNA-binding transcription factors, promote salt tolerance in upland cotton

KEY MESSAGE

The utilization of transcriptome analysis, functional validation, VIGS, and DAB techniques have provided evidence that GhiPLATZ17 and GhiPLATZ22 play a pivotal role in improving the salt tolerance of upland cotton. PLATZ (Plant AT-rich sequences and zinc-binding proteins) are known to be key regulators in plant growth, development, and response to salt stress. In this study, we comprehensively analyzed the PLATZ family in ten cotton species in response to salinity stress. Gossypium herbaceum boasts 25 distinct PLATZ genes, paralleled by 24 in G. raimondii, 25 in G. arboreum, 46 in G. hirsutum, 48 in G. barbadense, 43 in G. tomentosum, 67 in G. mustelinum, 60 in G. darwinii, 46 in G. ekmanianum, and a total of 53 PLATZ genes attributed to G. stephensii. The PLATZ gene family shed light on the hybridization and allopolyploidy events that occurred during the evolutionary history of allotetraploid cotton. Ka/Ks analysis suggested that the PLATZ gene family underwent intense purifying selection during cotton evolution. Analysis of synteny and gene collinearity revealed a complex pattern of segmental and dispersed duplication events to expand PLATZ genes in cotton. Cis-acting elements and gene expressions revealed that GhiPLATZ exhibited salt stress resistance. Transcriptome analysis, functional validation, virus-induced gene silencing (VIGS), and diaminobenzidine staining (DAB) demonstrated that GhiPLATZ17 and GhiPLATZ22 enhance salt tolerance in upland cotton. The study can potentially advance our understanding of identifying salt-resistant genes in cotton.

Lignin reduction in sugarcane by performing CRISPR/Cas9 site-direct mutation of SoLIM transcription factor

Genetic engineering of plant cell walls is limited for reducing lignocellulose recalcitrance, so mild and/or green-like pretreatment is still required for sequential enzymatic saccharification. Here, we report a method to reduce lignin content in sugarcane stalks using the CRISPR/Cas 9 technique. Three target sequences of SoLIM were designed and fused to pRGEB32. The cassette constructs were introduced into sugarcane calli cv. KK3 through Agrobacterium-mediated transformation. We produced one base substitution and one insertion line for the 1st target site; two insertions, one deletion, and one base substitution for the 2nd target site; and one base substitution and insertion for the 3rd target site. qRT-PCR analysis of SoLIM, SoPAL, SoC4H, and SoCAD showeded that downregulation of SoLIM by single nucleotide insertions or deletions reduced the expression of SoPAL, SoC4H, and SoCAD. Consequently, the edited lines contained 9.74 to 51.46% less lignin content compared to that in the wild-type plants. The syringyl/guaiacyl (S/G) ratio of the edited lines ranged between 0.23 and 0.49, while the wild-type was 0.22. The histochemical evaluation and scanning electron microscopy of the cell walls supported this observation. A low lignin content sugarcane will provide a better feedstock for second-generation bioethanol production.

Genes expression profiles in vascular cambium of Eucalyptus urophylla × Eucalyptus grandis at different ages

BACKGROUND

Wood is a secondary xylem generated by vascular cambium. Vascular cambium activities mainly include cambium proliferation and vascular tissue formation through secondary growth, thereby producing new secondary phloem inward and secondary xylem outward and leading to continuous tree thickening and wood formation. Wood formation is a complex biological process, which is strictly regulated by multiple genes. Therefore, molecular level research on the vascular cambium of different tree ages can lead to the identification of both key and related genes involved in wood formation and further explain the molecular regulation mechanism of wood formation.

RESULTS

In the present study, RNA-Seq and Pac-Bio Iso-Seq were used for profiling gene expression changes in Eucalyptus urophylla × Eucalyptus grandis (E. urograndis) vascular cambium at four different ages. A total of 59,770 non-redundant transcripts and 1892 differentially expressed genes (DEGs) were identified. The expression trends of the DEGs related to cell division and differentiation, cell wall biosynthesis, phytohormone, and transcription factors were analyzed. The DEGs encoding expansin, kinesin, cycline, PAL, GRP9, KNOX, C2C2-dof, REV, etc., were highly expressed in E. urograndis at three years old, leading to positive effects on growth and development. Moreover, some gene family members, such as NAC, MYB, HD-ZIP III, RPK, and RAP, play different regulatory roles in wood formation because of their sophisticated transcriptional network and function redundantly.

CONCLUSIONS

These candidate genes are a potential resource to further study wood formation, especially in fast-growing and adaptable eucalyptus. The results may also serve as a basis for further research to unravel the molecular mechanism underlying wood formation.

Stone cell formation in the pedicel of pears and apples

MAIN CONCLUSION

For the first time, stone cells in pear and apple pedicel were studied. The lignification of the pedicel outer part was correlated with flesh, and the secondary cell wall biosynthesis genes were activated. Fruit pedicels act as bridges between the fruit and the shoot. They have secondary thickened cell walls that presumably function in mechanical support, water and nutrient transport. Stone cells are cells with a secondary cell wall thickening. In pears, yet not in apples, the stone cells affect the flesh texture. There have been few reports on stone cell formation in pear and apple pedicels; therefore, we studied these cells for the first time. The apple pedicel had few stone cells in the cortex. The formation of stone cells in pear continued until seven weeks after flowering (WAF), and the density was significantly higher than in apple. The stone cell formation degree (SFD) of pear was 3.6-7.1 times higher than that of apple. Total lignin and lignin non-condensed structure (G and S units) content in the pear pedicle outer part was 1.5-2.7 times higher than that of the apple at harvest. The SFD of the pedicel outer part had a positive correlation with the G and S units content of the flesh. The total lignin and G and S units content between flesh and the pedicel outer part were positively correlated. Correlation analysis revealed a positive relationship between fruit and pedicel formation of the stone cells. The WGCNA showed that NST3 was linked to NAC028, MYB46, CESA, POD, LAC, and VSR6. These genes were highly expressed in the outer part of the pear pedicel, while they were suppressed in that issue of the apple at 4 WAF.

Genome-Wide Identification and Expression Analysis of the PLATZ Transcription Factor in Tomato

The PLATZ (plant AT protein and zinc-binding protein) transcription factor family is involved in the regulation of plant growth and development and plant stress response. In this study, 24 SlPLATZs were identified from the cultivated tomato genome and classified into four groups based on the similarity of conserved patterns among members of the same subfamily. Fragment duplication was an important way to expand the SlPLATZ gene family in tomatoes, and the sequential order of tomato PLATZ genes in the evolution of monocotyledonous and dicotyledonous plants and the roles they played were hypothesized. Expression profiles based on quantitative real-time reverse transcription PCR showed that SlPLATZ was involved in the growth of different tissues in tomatoes. SlPLATZ21 acts mainly in the leaves. SlPLATZ9, SlPLATZ21, and SlPLATZ23 were primarily involved in the red ripening, expanding, and mature green periods of fruit, respectively. In addition, SlPLATZ1 was found to play an important role in salt stress. This study will lay the foundation for the analysis of the biological functions of SlPLATZ genes and will also provide a theoretical basis for the selection and breeding of new tomato varieties and germplasm innovation.

Design, execution, and interpretation of plant RNA-seq analyses

Genomics has transformed our understanding of the genetic architecture of traits and the genetic variation present in plants. Here, we present a review of how RNA-seq can be performed to tackle research challenges addressed by plant sciences. We discuss the importance of experimental design in RNA-seq, including considerations for sampling and replication, to avoid pitfalls and wasted resources. Approaches for processing RNA-seq data include quality control and counting features, and we describe common approaches and variations. Though differential gene expression analysis is the most common analysis of RNA-seq data, we review multiple methods for assessing gene expression, including detecting allele-specific gene expression and building co-expression networks. With the production of more RNA-seq data, strategies for integrating these data into genetic mapping pipelines is of increased interest. Finally, special considerations for RNA-seq analysis and interpretation in plants are needed, due to the high genome complexity common across plants. By incorporating informed decisions throughout an RNA-seq experiment, we can increase the knowledge gained.

Genome-wide analysis of MdPLATZ genes and their expression during axillary bud outgrowth in apple (Malus domestica Borkh.)

BACKGROUND

Branching is a plastic character that affects plant architecture and spatial structure. The trait is controlled by a variety of plant hormones through coordination with environmental signals. Plant AT-rich sequence and zinc-binding protein (PLATZ) is a transcription factor that plays an important role in plant growth and development. However, systematic research on the role of the PLATZ family in apple branching has not been conducted previously.

RESULTS

In this study, a total of 17 PLATZ genes were identified and characterized from the apple genome. The 83 PLATZ proteins from apple, tomato, Arabidopsis, rice, and maize were classified into three groups based on the topological structure of the phylogenetic tree. The phylogenetic relationships, conserved motifs, gene structure, regulatory cis-acting elements, and microRNAs of the MdPLATZ family members were predicted. Expression analysis revealed that MdPLATZ genes exhibited distinct expression patterns in different tissues. The expression patterns of the MdPLATZ genes were systematically investigated in response to treatments that impact apple branching [thidazuron (TDZ) and decapitation]. The expression of MdPLATZ1, 6, 7, 8, 9, 15, and 16 was regulated during axillary bud outgrowth based on RNA-sequencing data obtained from apple axillary buds treated by decapitation or exogenous TDZ application. Quantitative real-time PCR analysis showed that MdPLATZ6 was strongly downregulated in response to the TDZ and decapitation treatments, however, MdPLATZ15 was significantly upregulated in response to TDZ, but exhibited little response to decapitation. Furthermore, the co-expression network showed that PLATZ might be involved in shoot branching by regulating branching-related genes or mediating cytokinin or auxin pathway.

CONCLUSION

The results provide valuable information for further functional investigation of MdPLATZ genes in the control of axillary bud outgrowth in apple.

Transcriptomic and Proteomic Landscape of Sugarcane Response to Biotic and Abiotic Stressors

Sugarcane, a C₄ plant, provides most of the world's sugar, and a substantial amount of renewable bioenergy, due to its unique sugar-accumulating and feedstock properties. Brazil, India, China, and Thailand are the four largest sugarcane producers worldwide, and the crop has the potential to be grown in arid and semi-arid regions if its stress tolerance can be improved. Modern sugarcane cultivars which exhibit a greater extent of polyploidy and agronomically important traits, such as high sugar concentration, biomass production, and stress tolerance, are regulated by complex mechanisms. Molecular techniques have revolutionized our understanding of the interactions between genes, proteins, and metabolites, and have aided in the identification of the key regulators of diverse traits. This review discusses various molecular techniques for dissecting the mechanisms underlying the sugarcane response to biotic and abiotic stresses. The comprehensive characterization of sugarcane's response to various stresses will provide targets and resources for sugarcane crop improvement.

Identification of the egusi seed trait locus (eg) and its suppressor gene associated with the thin seed coat trait in watermelon

Egusi watermelon has a unique egusi seed type, which could be useful for breeding both edible seeds and edible flesh in watermelon. However, the genetic basis of the unique egusi seed type is not clear. In the present study, we first reported that at least two genes with inhibitory epistasis were responsible for the thin seed coat (unique egusi seed type) in watermelon. Inheritance analysis of five populations, including F₂, BC, and BCF₂, suggested that the thin seed coat trait was controlled by a suppressor gene together with the egusi seed locus (eg) in egusi watermelon. Based on high-throughput sequencing technology, two quantitative trait loci located on chromosome 1 and chromosome 6 were identified for the thin seed coat trait in watermelon. One of the loci, the eg locus on chromosome 6, was finely mapped to a genomic region of 15.7 kb, which contained only one candidate gene. Comparative transcriptome analysis highlighted differentially expressed genes involved in cellulose and lignin synthesis between watermelon genotypes varying in the thickness of the seed coat and provided several potential candidate genes for the thin seed coat trait. Taken together, our data suggest that at least two genes are complementarily involved in the thin seed coat trait and will be useful for cloning novel genes. The results presented here provide a new reference for uncovering egusi seed genetic mechanisms and valuable information for marker-assisted selection in seed coat breeding.

Genome-Wide Identification and Phylogenetic and Expression Analyses of the PLATZ Gene Family in Medicago sativa L

The PLATZ family is a novel class of plant-specific zinc finger transcription factors with important roles in plant growth and development and abiotic stress responses. PLATZ members have been identified in many plants, including Oryza sativa, Zea mays, Triticum aestivum, Fagopyrum tataricum, and Arabidopsis thaliana; however, due to the complexity of the alfalfa reference genome, the members of the PLATZ gene family in alfalfa (Medicago sativa L.) have not been systematically identified and analyzed. In this study, 55 Medicago sativa PLATZ genes (MsPLATZs) were identified in the alfalfa "Xinjiangdaye" reference genome. Basic bioinformatic analysis was performed, including the characterization of sequence lengths, protein molecular weights, genomic positions, and conserved motifs. Expression analysis reveals that 7 MsPLATZs are tissue-specifically expressed, and 10 MsPLATZs are expressed in all examined tissues. The transcriptomic expression of these genes is obvious, indicating that these MsPLATZs have different functions in the growth and development of alfalfa. Based on transcriptome data analysis and real-time quantitative PCR (RT-qPCR), we identified 22, 22, and 21 MsPLATZ genes that responded to salt, cold, and drought stress, respectively, with 20 MsPLATZs responding to all three stresses. This study lays a foundation for further exploring the functions of MsPLATZs, and provides ideas for the improvement of alfalfa varieties and germplasm innovation.

Identification and characterization of Dof genes in Cerasus humilis

Introduction

Dof genes encode plant-specific transcription factors, which regulate various biological processes such as growth, development, and secondary metabolite accumulation.

Methods

We conducted whole-genome analysis of Chinese dwarf cherry (Cerasus humilis) to identify ChDof genes and characterize the structure, motif composition, cis-acting elements, chromosomal distribution, and collinearity of these genes as well as the physical and chemical properties, amino acid sequences, and phylogenetic evolution of the encoded proteins.

Results

The results revealed the presence of 25 ChDof genes in C. humilis genome. All 25 ChDof genes could be divided into eight groups, and the members of the same group had similar motif arrangement and intron-exon structure. Promoter analysis showed that cis-acting elements responsive to abscisic acid, low temperature stress, and light were dominant. Transcriptome data revealed that most ChDof genes exhibited tissue-specific expression. Then, we performed by qRT-PCR to analyze the expression patterns of all 25 ChDof genes in fruit during storage. The results indicated that these genes exhibited different expression patterns, suggesting that they played an important role in fruit storage.

Discussion

The results of this study provide a basis for further investigation of the biological function of Dof genes in C. humilis fruit.

Integrative System Biology Analysis of Transcriptomic Responses to Drought Stress in Soybean (Glycine max L.)

Drought is a major abiotic stressor that causes yield losses and limits the growing area for most crops. Soybeans are an important legume crop that is sensitive to water-deficit conditions and suffers heavy yield losses from drought stress. To improve drought-tolerant soybean cultivars through breeding, it is necessary to understand the mechanisms of drought tolerance in soybeans. In this study, we applied several transcriptome datasets obtained from soybean plants under drought stress in comparison to those grown under normal conditions to identify novel drought-responsive genes and their underlying molecular mechanisms. We found 2168 significant up/downregulated differentially expressed genes (DEGs) and 8 core modules using gene co-expression analysis to predict their biological roles in drought tolerance. Gene Ontology and KEGG analyses revealed key biological processes and metabolic pathways involved in drought tolerance, such as photosynthesis, glyceraldehyde-3-phosphate dehydrogenase and cytokinin dehydrogenase activity, and regulation of systemic acquired resistance. Genome-wide analysis of plants' cis-acting regulatory elements (CREs) and transcription factors (TFs) was performed for all of the identified DEG promoters in soybeans. Furthermore, the PPI network analysis revealed significant hub genes and the main transcription factors regulating the expression of drought-responsive genes in each module. Among the four modules associated with responses to drought stress, the results indicated that GLYMA_04G209700, GLYMA_02G204700, GLYMA_06G030500, GLYMA_01G215400, and GLYMA_09G225400 have high degrees of interconnection and, thus, could be considered as potential candidates for improving drought tolerance in soybeans. Taken together, these findings could lead to a better understanding of the mechanisms underlying drought responses in soybeans, which may useful for engineering drought tolerance in plants.

A joint learning approach for genomic prediction in polyploid grasses

Poaceae, among the most abundant plant families, includes many economically important polyploid species, such as forage grasses and sugarcane (Saccharum spp.). These species have elevated genomic complexities and limited genetic resources, hindering the application of marker-assisted selection strategies. Currently, the most promising approach for increasing genetic gains in plant breeding is genomic selection. However, due to the polyploidy nature of these polyploid species, more accurate models for incorporating genomic selection into breeding schemes are needed. This study aims to develop a machine learning method by using a joint learning approach to predict complex traits from genotypic data. Biparental populations of sugarcane and two species of forage grasses (Urochloa decumbens, Megathyrsus maximus) were genotyped, and several quantitative traits were measured. High-quality markers were used to predict several traits in different cross-validation scenarios. By combining classification and regression strategies, we developed a predictive system with promising results. Compared with traditional genomic prediction methods, the proposed strategy achieved accuracy improvements exceeding 50%. Our results suggest that the developed methodology could be implemented in breeding programs, helping reduce breeding cycles and increase genetic gains.

Impact of Agroclimatic Variables on Proteogenomics in Sugar Cane (Saccharum spp.) Plant Productivity

Sugar cane (Saccharum spp. hybrids) is a major crop for sugar and renewable bioenergy worldwide, grown in arid and semiarid regions. China, the world's fourth-largest sugar producer after Brazil, India, and the European Union, all share ∼80% of the global production, and the remaining ∼20% of sugar comes from sugar beets, mostly grown in the temperate regions of the Northern Hemisphere, also used as a raw material in production of bioethanol for renewable energy. In view of carboxylation strategies, sugar cane qualifies as one of the best C4 crop. It has dual CO2 concentrating mechanisms located in its unique Krantz anatomy, having dimorphic chloroplasts located in mesophylls and bundle sheath cells for integrated operation of C4 and C3 carbon fixation cycles, regulated by enzymes to upgrade/sustain an ability for improved carbon assimilation to acquire an optimum carbon economy by producing enhanced plant biomass along with sugar yield under elevated temperature and strong irradiance with improved water-use efficiency. These superior intrinsic physiological carbon metabolisms encouraged us to reveal and recollect the facts for moving ahead with the molecular approaches to reveal the expression of proteogenomics linked with plant productivity under abiotic stress during its cultivation in specific agrizones globally.

Spatio-Temporal Modification of Lignin Biosynthesis in Plants: A Promising Strategy for Lignocellulose Improvement and Lignin Valorization

Lignin is essential for plant growth, structural integrity, biotic/abiotic stress resistance, and water transport. Besides, lignin constitutes 10–30% of lignocellulosic biomass and is difficult to utilize for biofuel production. Over the past few decades, extensive research has uncovered numerous metabolic pathways and genes involved in lignin biosynthesis, several of which have been highlighted as the primary targets for genetic manipulation. However, direct manipulation of lignin biosynthesis is often associated with unexpected abnormalities in plant growth and development for unknown causes, thus limiting the usefulness of genetic engineering for biomass production and utilization. Recent advances in understanding the complex regulatory mechanisms of lignin biosynthesis have revealed new avenues for spatial and temporal modification of lignin in lignocellulosic plants that avoid growth abnormalities. This review explores recent work on utilizing specific transcriptional regulators to modify lignin biosynthesis at both tissue and cellular levels, focusing on using specific promoters paired with functional or regulatory genes to precisely control lignin synthesis and achieve biomass production with desired properties. Further advances in designing more appropriate promoters and other regulators will increase our capacity to modulate lignin content and structure in plants, thus setting the stage for high-value utilization of lignin in the future.

Internode elongation in energy cane shows remarkable clues on lignocellulosic biomass biosynthesis in Saccharum hybrids

Energy cane is a dedicated crop to high biomass production and selected during Saccharum breeding programs to fit specific industrial needs for 2G bioethanol production. Internode elongation is one of the most important characteristics in Saccharum hybrids due to its relationship with crop yield. In this study, we selected the third internode elongation of the energy cane. To characterize this process, we divided the internode into five sections and performed a detailed transcriptome analysis (RNA-Seq) and cell wall characterization. The histological analyses revealed a remarkable gradient that spans from cell division and protoxylem lignification to the internode maturation and complete vascular bundle lignification. RNA-Seq analysis revealed more than 11,000 differentially expressed genes between the sections internal. Gene ontology analyzes showed enriched categories in each section, as well as the most expressed genes in each section, presented different biological processes. We found that the internode elongation and division zones have a large number of unique genes. Evaluated the specific profile of genes related to primary and secondary cell wall formation, cellulose synthesis, hemicellulose, lignin, and growth-related genes. For each section these genes presented different profiles along the internode in elongation in energy cane. The results of this study provide an overview of the regulation of gene expression of an internode elongation in energy cane. Gene expression analysis revealed promising candidates for transcriptional regulation of energy cane lignification and evidence key genes for the regulation of internode development, which can serve as a basis for understanding the molecular regulatory mechanisms that support the growth and development of plants in the Saccahrum complex.

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

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

Allele expression biases in mixed-ploid sugarcane accessions

Allele-specific expression (ASE) represents differences in the magnitude of expression between alleles of the same gene. This is not straightforward for polyploids, especially autopolyploids, as knowledge about the dose of each allele is required for accurate estimation of ASE. This is the case for the genomically complex Saccharum species, characterized by high levels of ploidy and aneuploidy. We used a Beta-Binomial model to test for allelic imbalance in Saccharum, with adaptations for mixed-ploid organisms. The hierarchical Beta-Binomial model was used to test if allele expression followed the expectation based on genomic allele dosage. The highest frequencies of ASE occurred in sugarcane hybrids, suggesting a possible influence of interspecific hybridization in these genotypes. For all accessions, genes showing ASE (ASEGs) were less frequent than those with balanced allelic expression. These genes were related to a broad range of processes, mostly associated with general metabolism, organelles, responses to stress and responses to stimuli. In addition, the frequency of ASEGs in high-level functional terms was similar among the genotypes, with a few genes associated with more specific biological processes. We hypothesize that ASE in Saccharum is largely a genotype-specific phenomenon, as a large number of ASEGs were exclusive to individual accessions.

Transcriptome changes in the developing sugarcane culm associated with high yield and early-season high sugar content

Sugarcane, with its exceptional carbon dioxide assimilation, biomass and sugar yield, has a high potential for the production of bio-energy, bio-plastics and high-value products in the food and pharmaceutical industries. A crucial challenge for long-term economic viability and environmental sustainability is also to optimize the production of biomass composition and carbon sequestration. Sugarcane varieties such as KQ228 and Q253 are highly utilized in the industry. These varieties are characterized by a high early-season sugar content associated with high yield. In order to investigate these correlations, 1,440 internodes were collected and combined to generate a set of 120 samples in triplicate across 24 sugarcane cultivars at five different development stages. Weighted gene co-expression network analysis (WGCNA) was used and revealed for the first time two sets of co-expressed genes with a distinct and opposite correlation between fibre and sugar content. Gene identification and metabolism pathways analysis was used to define these two sets of genes. Correlation analysis identified a large number of interconnected metabolic pathways linked to sugar content and fibre content. Unsupervised hierarchical clustering of gene expression revealed a stronger level of segregation associated with the genotypes than the stage of development, suggesting a dominant genetic influence on biomass composition and facilitating breeding selection. Characterization of these two groups of co-expressed key genes can help to improve breeding program for high fibre, high sugar species or plant synthetic biology.

The Pivotal Role of Major Chromosomes of Sub-Genomes A and D in Fiber Quality Traits of Cotton

Lack of precise information about the candidate genes involved in a complex quantitative trait is a major obstacle in the cotton fiber quality improvement, and thus, overall genetic gain in conventional phenotypic selection is low. Recent molecular interventions and advancements in genome sequencing have led to the development of high-throughput molecular markers, quantitative trait locus (QTL) fine mapping, and single nucleotide polymorphisms (SNPs). These advanced tools have resolved the existing bottlenecks in trait-specific breeding. This review demonstrates the significance of chromosomes 3, 7, 9, 11, and 12 of sub-genomes A and D carrying candidate genes for fiber quality. However, chromosome 7 carrying SNPs for stable and potent QTLs related to fiber quality provides great insights for fiber quality-targeted research. This information can be validated by marker-assisted selection (MAS) and transgene in Arabidopsis and subsequently in cotton.

Transcriptome Analysis Reveals a Gene Expression Pattern That Contributes to Sugarcane Bud Propagation Induced by Indole-3-Butyric Acid

Sugarcane is a cash crop that plays an integral part in the sugar industry. The Sustainable Sugarcane Initiative (SSI) has been adopted globally, ensuring enough and aiming for more yield, helping increase disease-free sugarcane cultivation. Single-bud seeds could be the best approach for sugarcane cultivation. Indole-3-butyric acid (IBA) is a rooting agent utilized significantly in seedling propagation. Greenhouse experiment results discovered the significant growth promotion in sugarcane seedlings and accumulation of plant hormones at 100 ppm IBA. Next, we performed transcriptomic analysis of sugarcane buds using RNA sequencing and compared their gene expression during root development due to affect of IBA (100 ppm). A total of 113,475 unigenes were annotated with an average length of 836 bp (N50 = 1,536). The comparative RNA-seq study between the control (CK) and IBA-treated (T) buds showed significant differentially expressed unigenes (494 upregulated and 2086 downregulated). The IBA influenced major biological processes including metabolic process, the cellular process, and single-organism process. For cellular component category, cell, cell part, organelle, membrane, and organelle part were mainly affected. In addition, catalytic activity and binding were primarily affected in the molecular function categories. Furthermore, the expression of genes related to plant hormones and signaling pathways was analyzed by qRT-PCR, which was consistent with the RNA-seq expression profile. This study provides new insights into the IBA response to the bud sprouting in sugarcane based on RNA sequencing, and generated information could help further research on breeding improvement of sugarcane.

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

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

Comparative de novo transcriptome analysis identifies salinity stress responsive genes and metabolic pathways in sugarcane and its wild relative Erianthus arundinaceus [Retzius] Jeswiet

Erianthus arundinaceus [Retzius] Jeswiet, a wild relative of sugarcane has a high biomass production potential and a reservoir of many genes for superior agronomic traits and tolerance to biotic and abiotic stresses. A comparative physiological, anatomical and root transcriptome analysis were carried out to identify the salt-responsive genes and metabolic pathways associated with salt-tolerant E. arundinaceus genotype IND99-907 and salinity-sensitive sugarcane genotype Co 97010. IND99-907 recorded growth of young leaves, higher proline content, higher relative water content, intact root anatomical structures and lower Na+/K+, Ca2+/K+ and Mg2+/K+ ratio as compared to the sugarcane genotype Co 97010. We have generated four de novo transcriptome assemblies between stressed and control root samples of IND99-907 and Co 97010. A total of 649 and 501 differentially expressed genes (FDR<0.01) were identified from the stressed and control libraries of IND99-907 and Co 97010 respectively. Genes and pathways related to early stress-responsive signal transduction, hormone signalling, cytoskeleton organization, cellular membrane stabilization, plasma membrane-bound calcium and proton transport, sodium extrusion, secondary metabolite biosynthesis, cellular transporters related to plasma membrane-bound trafficking, nucleobase transporter, clathrin-mediated endocytosis were highly enriched in IND99-907. Whereas in Co 97010, genes related to late stress-responsive signal transduction, electron transport system, senescence, protein degradation and programmed cell death, transport-related genes associated with cellular respiration and mitochondrial respiratory chain, vesicular trafficking, nitrate transporter and fewer secondary metabolite biosynthetic genes were highly enriched. A total of 27 pathways, 24 biological processes, three molecular functions and one cellular component were significantly enriched (FDR≤ 0.05) in IND99-907 as compared to 20 pathways, two biological processes without any significant molecular function and cellular components in Co 97010, indicates the unique and distinct expression pattern of genes and metabolic pathways in both genotypes. The genomic resources developed from this study is useful for sugarcane crop improvement through development of genic SSR markers and genetic engineering approaches.

Temporal Gene Expression in Apical Culms Shows Early Changes in Cell Wall Biosynthesis Genes in Sugarcane

Multiple genes in sugarcane control sucrose accumulation and the biosynthesis of cell wall components; however, it is unclear how these genes are expressed in its apical culms. To better understand this process, we sequenced mRNA from +1 stem internodes collected from four genotypes with different concentrations of soluble solids. Culms were collected at four different time points, ranging from six to 12-month-old plants. Here we show differentially expressed genes related to sucrose metabolism and cell wall biosynthesis, including genes encoding invertases, sucrose synthase and cellulose synthase. Our results showed increased expression of invertases in IN84-58, the genotype with lower sugar and higher fiber content, as well as delayed expression of secondary cell wall-related cellulose synthase for the other genotypes. Interestingly, genes involved with hormone metabolism were differentially expressed across time points in the three genotypes with higher soluble solids content. A similar result was observed for genes controlling maturation and transition to reproductive stages, possibly a result of selection against flowering in sugarcane breeding programs. These results indicate that carbon partitioning in apical culms of contrasting genotypes is mainly associated with differential cell wall biosynthesis, and may include early modifications for subsequent sucrose accumulation. Co-expression network analysis identified transcription factors related to growth and development, showing a probable time shift for carbon partitioning occurred in 10-month-old plants.

Planting Season Impacts Sugarcane Stem Development, Secondary Metabolite Levels, and Natural Antisense Transcription

To reduce the potentially irreversible environmental impacts caused by fossil fuels, the use of renewable energy sources must be increased on a global scale. One promising source of biomass and bioenergy is sugarcane. The study of this crop's development in different planting seasons can aid in successfully cultivating it in global climate change scenarios. The sugarcane variety SP80-3280 was field grown under two planting seasons with different climatic conditions. A systems biology approach was taken to study the changes on physiological, morphological, agrotechnological, transcriptomics, and metabolomics levels in the leaf +1, and immature, intermediate and mature internodes. Most of the variation found within the transcriptomics and metabolomics profiles is attributed to the differences among the distinct tissues. However, the integration of both transcriptomics and metabolomics data highlighted three main metabolic categories as the principal sources of variation across tissues: amino acid metabolism, biosynthesis of secondary metabolites, and xenobiotics biodegradation and metabolism. Differences in ripening and metabolite levels mainly in leaves and mature internodes may reflect the impact of contrasting environmental conditions on sugarcane development. In general, the same metabolites are found in mature internodes from both "one-year" and "one-and-a-half-year sugarcane", however, some metabolites (i.e., phenylpropanoids with economic value) and natural antisense transcript expression are only detected in the leaves of "one-year" sugarcane.

Modern Biotechnologies: Innovative and Sustainable Approaches for the Improvement of Sugarcane Tolerance to Environmental Stresses

Sugarcane (Saccharum spp.) is one of the most important industrial cash crops, contributing to the world sugar industry and biofuel production. It has been cultivated and improved from prehistoric times through natural selection and conventional breeding and, more recently, using the modern tools of genetic engineering and biotechnology. However, the heterogenicity, complex poly-aneuploid genome and susceptibility of sugarcane to different biotic and abiotic stresses represent impediments that require us to pay greater attention to the improvement of the sugarcane crop. Compared to traditional breeding, recent advances in breeding technologies (molecular marker-assisted breeding, sugarcane transformation, genome-editing and multiple omics technologies) can potentially improve sugarcane, especially against environmental stressors. This article will focus on efficient modern breeding technologies, which provide crucial clues for the engineering of sugarcane cultivars resistant to environmental stresses.

Association of gene expression with syringyl to guaiacyl ratio in sugarcane lignin

A transcriptome analysis reveals the transcripts and alleles differentially expressed in sugarcane genotypes with contrasting lignin composition. Sugarcane bagasse is a highly abundant resource that may be used as a feedstock for the production of biofuels and bioproducts in order to meet increasing demands for renewable replacements for fossil carbon. However, lignin imparts rigidity to the cell wall that impedes the efficient breakdown of the biomass into fermentable sugars. Altering the ratio of the lignin units, syringyl (S) and guaiacyl (G), which comprise the native lignin polymer in sugarcane, may facilitate the processing of bagasse. This study aimed to identify genes and markers associated with S/G ratio in order to accelerate the development of sugarcane bioenergy varieties with modified lignin composition. The transcriptome sequences of 12 sugarcane genotypes that contrasted for S/G ratio were compared and there were 2019 transcripts identified as differentially expressed (DE) between the high and low S/G ratio groups. These included transcripts encoding possible monolignol biosynthetic pathway enzymes, transporters, dirigent proteins and transcriptional and post-translational regulators. Furthermore, the frequencies of single nucleotide polymorphisms (SNPs) were compared between the low and high S/G ratio groups to identify specific alleles expressed with the phenotype. There were 2063 SNP loci across 787 unique transcripts that showed group-specific expression. Overall, the DE transcripts and SNP alleles identified in this study may be valuable for breeding sugarcane varieties with altered S/G ratio that may provide desirable bioenergy traits.

Physiological changes and transcriptome profiling in Saccharum spontaneum L. leaf under water stress and re-watering conditions

As the polyploidy progenitor of modern sugarcane, Saccharum spontaneum is considered to be a valuable resistance source to various biotic and abiotic stresses. However, little has been reported on the mechanism of drought tolerance in S. spontaneum. Herein, the physiological changes of S. spontaneum GXS87-16 at three water-deficit levels (mild, moderate, and severe) and after re-watering during the elongation stage were investigated. RNA sequencing was utilized for global transcriptome profiling of GXS87-16 under severe drought and re-watered conditions. There were significant alterations in the physiological parameters of GXS87-16 in response to drought stress and then recovered differently after re-watering. A total of 1569 differentially expressed genes (DEGs) associated with water stress and re-watering were identified. Notably, the majority of the DEGs were induced by stress. GO functional annotations and KEGG pathway analysis assigned the DEGs to 47 GO categories and 93 pathway categories. The pathway categories were involved in various processes, such as RNA transport, mRNA surveillance, plant hormone signal transduction, and plant-pathogen interaction. The reliability of the RNA-seq results was confirmed by qRT-PCR. This study shed light on the regulatory processes of drought tolerance in S. spontaneum and identifies useful genes for genetic improvement of drought tolerance in sugarcane.

Genome-wide analysis of general phenylpropanoid and monolignol-specific metabolism genes in sugarcane

Lignin is the main component of secondary cell walls and is essential for plant development and defense. However, lignin is recognized as a major recalcitrant factor for efficiency of industrial biomass processing. Genes involved in general phenylpropanoid and monolignol-specific metabolism in sugarcane have been previously analyzed at the transcriptomic level. Nevertheless, the number of genes identified in this species is still very low. The recently released sugarcane genome sequence has allowed the genome-wide characterization of the 11 gene families involved in the monolignol biosynthesis branch of the phenylpropanoid pathway. After an exhaustive analysis of sugarcane genomes, 438 haplotypes derived from 175 candidate genes from Saccharum spontaneum and 144 from Saccharum hybrid R570 were identified as associated with this biosynthetic route. The phylogenetic analyses, combined with the search for protein conserved residues involved in the catalytic activity of the encoded enzymes, were employed to identify the family members potentially involved in developmental lignification. Accordingly, 15 candidates were identified as bona fide lignin biosynthesis genes: PTAL1, PAL2, C4H4, 4CL1, HCT1, HCT2, C3'H1, C3'H2, CCoAOMT1, COMT1, F5H1, CCR1, CCR2, CAD2, and CAD7. For this core set of lignin biosynthetic genes, we searched for the chromosomal location, the gene expression pattern, the promoter cis-acting elements, and microRNA targets. Altogether, our results present a comprehensive characterization of sugarcane general phenylpropanoid and monolignol-specific genes, providing the basis for further functional studies focusing on lignin biosynthesis manipulation and biotechnological strategies to improve sugarcane biomass utilization.

Applying Molecular Phenotyping Tools to Explore Sugarcane Carbon Potential

Sugarcane (Saccharum spp.), a C₄ grass, has a peculiar feature: it accumulates, gradient-wise, large amounts of carbon (C) as sucrose in its culms through a complex pathway. Apart from being a sustainable crop concerning C efficiency and bioenergetic yield per hectare, sugarcane is used as feedstock for producing ethanol, sugar, high-value compounds, and products (e.g., polymers and succinate), and bioelectricity, earning the title of the world's leading biomass crop. Commercial cultivars, hybrids bearing high levels of polyploidy, and aneuploidy, are selected from a large number of crosses among suitable parental genotypes followed by the cloning of superior individuals among the progeny. Traditionally, these classical breeding strategies have been favoring the selection of cultivars with high sucrose content and resistance to environmental stresses. A current paradigm change in sugarcane breeding programs aims to alter the balance of C partitioning as a means to provide more plasticity in the sustainable use of this biomass for metabolic engineering and green chemistry. The recently available sugarcane genetic assemblies powered by data science provide exciting perspectives to increase biomass, as the current sugarcane yield is roughly 20% of its predicted potential. Nowadays, several molecular phenotyping tools can be applied to meet the predicted sugarcane C potential, mainly targeting two competing pathways: sucrose production/storage and biomass accumulation. Here we discuss how molecular phenotyping can be a powerful tool to assist breeding programs and which strategies could be adopted depending on the desired final products. We also tackle the advances in genetic markers and mapping as well as how functional genomics and genetic transformation might be able to improve yield and saccharification rates. Finally, we review how "omics" advances are promising to speed up plant breeding and reach the unexplored potential of sugarcane in terms of sucrose and biomass production.

Differential expression in leaves of Saccharum genotypes contrasting in biomass production provides evidence of genes involved in carbon partitioning

BACKGROUND

The development of biomass crops aims to meet industrial yield demands, in order to optimize profitability and sustainability. Achieving these goals in an energy crop like sugarcane relies on breeding for sucrose accumulation, fiber content and stalk number. To expand the understanding of the biological pathways related to these traits, we evaluated gene expression of two groups of genotypes contrasting in biomass composition.

RESULTS

First visible dewlap leaves were collected from 12 genotypes, six per group, to perform RNA-Seq. We found a high number of differentially expressed genes, showing how hybridization in a complex polyploid system caused extensive modifications in genome functioning. We found evidence that differences in transposition and defense related genes may arise due to the complex nature of the polyploid Saccharum genomes. Genotypes within both biomass groups showed substantial variability in genes involved in photosynthesis. However, most genes coding for photosystem components or those coding for phosphoenolpyruvate carboxylases (PEPCs) were upregulated in the high biomass group. Sucrose synthase (SuSy) coding genes were upregulated in the low biomass group, showing that this enzyme class can be involved with sucrose synthesis in leaves, similarly to sucrose phosphate synthase (SPS) and sucrose phosphate phosphatase (SPP). Genes in pathways related to biosynthesis of cell wall components and expansins coding genes showed low average expression levels and were mostly upregulated in the high biomass group.

CONCLUSIONS

Together, these results show differences in carbohydrate synthesis and carbon partitioning in the source tissue of distinct phenotypic groups. Our data from sugarcane leaves revealed how hybridization in a complex polyploid system resulted in noticeably different transcriptomic profiles between contrasting genotypes.

Differential expression between drought-tolerant and drought-sensitive sugarcane under mild and moderate water stress as revealed by a comparative analysis of leaf transcriptome

Sugarcane contributes 80% of global sugar production and to bioethanol generation for the bioenergy industry. Its productivity is threatened by drought that can cause up to 60% yield loss. This study used RNA-Seq to gain a better understanding of the underlying mechanism by which drought-tolerant sugarcane copes with water stress. We compared gene expression in KPS01-12 (drought-tolerant genotype) and UT12 (drought-sensitive genotype) that have significantly different yield loss rates under drought conditions. We treated KPS01-12 and UT12 with mild and moderate water stress and found differentially expressed genes in various biological processes. KPS01-12 had higher expression of genes that were involved in water retention, antioxidant secondary metabolite biosynthesis, and oxidative and osmotic stress response than UT12. In contrast, the sensitive genotype had more down-regulated genes that were involved in photosynthesis, carbon fixation and Calvin cycle than the tolerant genotype. Our obtained expression profiles suggest that the tolerant sugarcane has a more effective genetic response than the sensitive genotype at the initiation of drought stress. The knowledge gained from this study may be applied in breeding programs to improve sugarcane production in drought conditions.

Transcriptome Profiling Provides Molecular Insights into Auxin-Induced Adventitious Root Formation in Sugarcane (Saccharum spp. Interspecific Hybrids) Microshoots

Adventitious root (AR) formation was enhanced following the treatment of sugarcane microshoots with indole-3-butyric acid (IBA) and 1-naphthalene acetic acid (NAA) combined, suggesting that auxin is a positive regulator of sugarcane microshoot AR formation. The transcriptome profile identified 1737 and 1268 differentially expressed genes (DEGs) in the basal tissues (5 mm) of sugarcane microshoots treated with IBA+NAA compared to nontreated control on the 3rd and 7th days post-auxin or water treatment (days post-treatment—dpt), respectively. To understand the molecular changes, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed. This analysis showed that DEGs associated with the pathways were associated with plant hormone signaling, flavonoid and phenylpropanoid biosyntheses, cell cycle, and cell wall modification, and transcription factors could be involved in sugarcane microshoot AR formation. Furthermore, qRT–PCR analysis was used to validate the expression patterns of nine genes associated with root formation and growth, and the results were consistent with the RNA-seq results. Finally, a hypothetical hormonal regulatory working model of sugarcane microshoot AR formation is proposed. Our results provide valuable insights into the molecular processes associated with auxin-induced AR formation in sugarcane.

Phaeophyceaean (Brown Algal) Extracts Activate Plant Defense Systems in Arabidopsis thaliana Challenged With Phytophthora cinnamomi

Seaweed extracts are important sources of plant biostimulants that boost agricultural productivity to meet current world demand. The ability of seaweed extracts based on either of the Phaeophyceaean species Ascophyllum nodosum or Durvillaea potatorum to enhance plant growth or suppress plant disease have recently been shown. However, very limited information is available on the mechanisms of suppression of plant disease by such extracts. In addition, there is no information on the ability of a combination of extracts from A. nodosum and D. potatorum to suppress a plant pathogen or to induce plant defense. The present study has explored the transcriptome, using RNA-seq, of Arabidopsis thaliana following treatment with extracts from the two species, or a mixture of both, prior to inoculation with the root pathogen Phytophthora cinnamomi. Following inoculation, five time points (0-24 h post-inoculation) that represented early stages in the interaction of the pathogen with its host were assessed for each treatment and compared with their respective water controls. Wide scale transcriptome reprogramming occurred predominantly related to phytohormone biosynthesis and signaling, changes in metabolic processes and cell wall biosynthesis, there was a broad induction of proteolysis pathways, a respiratory burst and numerous defense-related responses were induced. The induction by each seaweed extract of defense-related genes coincident with the time of inoculation showed that the plants were primed for defense prior to infection. Each seaweed extract acted differently in inducing plant defense-related genes. However, major systemic acquired resistance (SAR)-related genes as well as salicylic acid-regulated marker genes (PR1, PR5, and NPR1) and auxin associated genes were found to be commonly up-regulated compared with the controls following treatment with each seaweed extract. Moreover, each seaweed extract suppressed P. cinnamomi growth within the roots of inoculated A. thaliana by the early induction of defense pathways and likely through ROS-based signaling pathways that were linked to production of ROS. Collectively, the RNA-seq transcriptome analysis revealed the induction by seaweed extracts of suites of genes that are associated with direct or indirect plant defense in addition to responses that require cellular energy to maintain plant growth during biotic stress.

Prime Editing Technology and Its Prospects for Future Applications in Plant Biology Research

Many applications in plant biology requires editing genomes accurately including correcting point mutations, incorporation of single-nucleotide polymorphisms (SNPs), and introduction of multinucleotide insertion/deletions (indels) into a predetermined position in the genome. These types of modifications are possible using existing genome-editing technologies such as the CRISPR-Cas systems, which require induction of double-stranded breaks in the target DNA site and the supply of a donor DNA molecule that contains the desired edit sequence. However, low frequency of homologous recombination in plants and difficulty of delivering the donor DNA molecules make this process extremely inefficient. Another kind of technology known as base editing can perform precise editing; however, only certain types of modifications can be obtained, e.g., C/G-to-T/A and A/T-to-G/C. Recently, a new type of genome-editing technology, referred to as "prime editing," has been developed, which can achieve various types of editing such as any base-to-base conversion, including both transitions (C→T, G→A, A→G, and T→C) and transversion mutations (C→A, C→G, G→C, G→T, A→C, A→T, T→A, and T→G), as well as small indels without the requirement for inducing double-stranded break in the DNA. Because prime editing has wide flexibility to achieve different types of edits in the genome, it holds a great potential for developing superior crops for various purposes, such as increasing yield, providing resistance to various abiotic and biotic stresses, and improving quality of plant product. In this review, we describe the prime editing technology and discuss its limitations and potential applications in plant biology research.

Molecular diversity and genetic structure of Saccharum complex accessions

Sugarcane is an important crop for food and energy security, providing sucrose and bioethanol from sugar content and bioelectricity from lignocellulosic bagasse. In order to evaluate the diversity and genetic structure of the Brazilian Panel of Sugarcane Genotypes (BPSG), a core collection composed by 254 accessions of the Saccharum complex, eight TRAP markers anchored in sucrose and lignin metabolism genes were evaluated. A total of 584 polymorphic fragments were identified and used to investigate the genetic structure of BPSG through analysis of molecular variance (AMOVA), principal components analysis (PCA), a Bayesian method using STRUCTURE software, genetic dissimilarity and phylogenetic tree. AMOVA showed a moderate genetic differentiation between ancestors and improved accessions, 0.14, and the molecular variance was higher within populations than among populations, with values of 86%, 95% and 97% when constrasting improved with ancestors, foreign with ancestors and improved with foreign, respectively. The PCA approach suggests clustering in according with evolutionary and Brazilian breeding sugarcane history, since improved accessions from older generations were positioned closer to ancestors than improved accessions from recent generations. This result was also confirmed by STRUCTURE analysis and phylogenetic tree. The Bayesian method was able to separate ancestors of the improved accessions while the phylogenetic tree showed clusters considering the family relatedness within three major clades; the first being composed mainly by ancestors and the other two mainly by improved accessions. This work can contribute to better management of the crosses considering functional regions of the sugarcane genome.

High-throughput sequencing reveals genes associated with high-temperature stress tolerance in sugarcane

Sugarcane (Saccharum spp.) is a major sugar crop grown in tropical and sub-tropical areas throughout the world which is vulnerable to high temperature stress due to climate change. In this present study, we have generated a transcriptome profile of sugarcane variety Co 99004 exposed to high-temperature stress (47 ^°C). The Illumina Nexseq2500 platform yielded a total of 39.28 and 13.44 million reads, corresponding to 3.9 and 1.3 gigabase pair (Gb) of the processed reads for control and high-temperature-stressed samples, respectively. Initially, the reads were de novo assembled into 118,017 unigenes with an average length of 780 bp. The longest sequence in the assembly was 21 kb. Further, these transcripts were BLASTed against GO, KEGG and COG databases to identify the novel genes/transcripts expressed due to elevated temperature conditions. The different expression analysis showed 1137 transcripts which were up-regulated during heat temperature stress when compared to control conditions. Analysis of relative gene expression showed phytepsin, ferredoxin-dependent glutamate synthase, and stress protein DDR-48 threefold increased expression during heat stress. These findings reveal novel targets for subsequent research on the genomics genetic manipulation and molecular mechanism of elevated stress tolerance in sugarcane.

Identification of genes from the general phenylpropanoid and monolignol-specific metabolism in two sugarcane lignin-contrasting genotypes

The phenylpropanoid pathway is an important route of secondary metabolism involved in the synthesis of different phenolic compounds such as phenylpropenes, anthocyanins, stilbenoids, flavonoids, and monolignols. The flux toward monolignol biosynthesis through the phenylpropanoid pathway is controlled by specific genes from at least ten families. Lignin polymer is one of the major components of the plant cell wall and is mainly responsible for recalcitrance to saccharification in ethanol production from lignocellulosic biomass. Here, we identified and characterized sugarcane candidate genes from the general phenylpropanoid and monolignol-specific metabolism through a search of the sugarcane EST databases, phylogenetic analysis, a search for conserved amino acid residues important for enzymatic function, and analysis of expression patterns during culm development in two lignin-contrasting genotypes. Of these genes, 15 were cloned and, when available, their loci were identified using the recently released sugarcane genomes from Saccharum hybrid R570 and Saccharum spontaneum cultivars. Our analysis points out that ShPAL1, ShPAL2, ShC4H4, Sh4CL1, ShHCT1, ShC3H1, ShC3H2, ShCCoAOMT1, ShCOMT1, ShF5H1, ShCCR1, ShCAD2, and ShCAD7 are strong candidates to be bona fide lignin biosynthesis genes. Together, the results provide information about the candidate genes involved in monolignol biosynthesis in sugarcane and may provide useful information for further molecular genetic studies in sugarcane.

Isolation, cloning and expression analysis of cinnamyl alcohol dehydrogenase (CAD) involved in phenylpropanoid pathway of Erianthus arundinaceus, a wild relative of sugarcane

In this study we have cloned and characterized cinnamyl alcohol dehydrogenase (CAD) involved in phenylpropanoid pathway which can be utilized for biomass modification for improved saccharification efficiency. The full length gene CAD is of 4 kb containing four exons and three introns, among which the exon 1 and 2 of 88 and 116 bp were conserved with sorghum and Miscanthus CADs. The coding region of CAD was identified with 1098 bp open reading frame (ORF), for 365 amino acids. In the PROSITE analysis, a zinc-containing alcohol dehydrogenase signature (GHEVVGEVVEVGPEV) and an NADP-binding domain motif (GLGGLG) was identified, while the motif analysis showed unique signature sequence of "LEPYLA" at 258-264 aa which was absent in the CAD sequences of other crops. This sequence information on CAD from Erianthus a bioenergy crop might be useful for subsequent research on lignin engineering for improved biomass conversion and for unravelling the impact of lignin on cell wall mechanics.

Genomic resources for energy cane breeding in the post genomics era

Sugarcane is one of the most sustainable energy crops among cultivated crops presenting the highest tonnage of cultivated plants. Its high productivity of sugar, bioethanol and bioelectricity make it a promising green alternative to petroleum. Furthermore, the myriad of products that can be derived from sugarcane biomass has been driving breeding programs towards varieties with a higher yield of fiber and a more vigorous and sustainable performance: the energy cane. Here we provide an overview of the energy cane including plant description, breeding efforts, types, and end-uses. In addition, we describe recently published genomic resources for the development of this crop, discuss current knowledge of cell wall metabolism, bioinformatic tools and databases available for the community.

Sugarcane Omics: An Update on the Current Status of Research and Crop Improvement

Sugarcane is an important crop from Poaceae family, contributing about 80% of the total world's sucrose with an annual value of around US$150 billion. In addition, sugarcane is utilized as a raw material for the production of bioethanol, which is an alternate source of renewable energy. Moving towards sugarcane omics, a remarkable success has been achieved in gene transfer from a wide variety of plant and non-plant sources to sugarcane, with the accessibility of efficient transformation systems, selectable marker genes, and genetic engineering gears. Genetic engineering techniques make possible to clone and characterize useful genes and also to improve commercially important traits in elite sugarcane clones that subsequently lead to the development of an ideal cultivar. Sugarcane is a complex polyploidy crop, and hence no single technique has been found to be the best for the confirmation of polygenic and phenotypic characteristics. To better understand the application of basic omics in sugarcane regarding agronomic characters and industrial quality traits as well as responses to diverse biotic and abiotic stresses, it is important to explore the physiology, genome structure, functional integrity, and collinearity of sugarcane with other more or less similar crops/plants. Genetic improvements in this crop are hampered by its complex genome, low fertility ratio, longer production cycle, and susceptibility to several biotic and abiotic stresses. Biotechnology interventions are expected to pave the way for addressing these obstacles and improving sugarcane crop. Thus, this review article highlights up to date information with respect to how advanced data of omics (genomics, transcriptomic, proteomics and metabolomics) can be employed to improve sugarcane crops.

Label-Free Quantitative Proteomics of Enriched Nuclei from Sugarcane (Saccharum ssp) Stems in Response to Drought Stress

Drought is considered the major abiotic stress limiting crop productivity. This study seeks to identify proteins involved in the drought response in sugarcane stems submitted to drought stress. The integration of nuclei enrichment sample preparation with the shotgun proteomic approach results in great coverage of the sugarcane stem proteome with 5381 protein groups identified. A total of 1204 differentially accumulated proteins are detected in response to drought, among which 586 and 618 are increased and reduced in abundance, respectively. A total of 115 exclusive proteins are detected, being 41 exclusives of drought-stressed plants and 74 exclusives of control plants. In the control plants, most of these proteins are related to cell wall metabolism, indicating that drought affects negatively the cell wall metabolism. Also, 37 transcription factors (TFs) are identified, which are low abundant nuclear proteins and are differentially accumulated in response to drought stress. These TFs are associated to protein domains such as leucine-rich (bZIP), C2H2, NAC, C3H, LIM, Myb-related, heat shock factor (HSF) and auxin response factor (ARF). Increased abundance of chromatin remodeling and RNA processing proteins are also observed. It is suggested that these variations result from an imbalance of protein synthesis and degradation processes induced by drought.

Genetic Basis of Fiber Improvement and Decreased Stress Tolerance in Cultivated Versus Semi-Domesticated Upland Cotton

Crop domestication from wild ancestors has resulted in the wide adaptation coupled with improved yield and quality traits. However, the genetic basis of many domesticated characteristics remains to be explored. Upland cotton (Gossypium hirsutum) is the most important tetraploid cotton species, accounting for about 90% of world cotton commerce. Here, we reveal the effects of domestication on fiber and stress traits through comprehensive analyses of semi-domesticated races and cultivated cotton accessions. A total of 416 cotton accessions were genotyped, and a decrease in genetic diversity from races to landraces and modern cultivars was detected. Furthermore, 71 domestication selective sweeps (DSS) and 14 improvement selective sweeps (ISS) were identified, with the Dt sub-genome experiencing stronger selection than the At sub-genome during the both selection types. The more expressed genes and a delay in the expression peak of genes related to secondary cell wall (SCW) development in modern cultivars compared to semi-domesticated cotton races, may have contributed to long fibers in these plants. However, down-regulation of genes related to stress response was responsible for decreasing stress tolerance in modern cultivars. We further experimentally confirmed that silencing of PR1 and WRKY20, genes that showed higher expression in the semi-domesticated races, drastically compromised cotton resistance to V. dahliae. Our results reveal fiber improvement and decreased stress tolerance as a result of the domestication of modern upland cotton cultivars.

Secondary Wall Regulating NACs Differentially Bind at the Promoter at a CELLULOSE SYNTHASE A4 Cis-eQTL

Arabidopsis thaliana CELLULOSE SYNTHASE A4/7/8 (CESA4/7/8) are three non-redundant subunits of the secondary cell wall cellulose synthase complex. Transcript abundance of these genes can vary among genotypes and expression quantitative trait loci (eQTL) were identified in a recombinant population of the accessions Bay-0 and Shahdara. Genetic mapping and analysis of the transcript levels of CESAs between two distinct near isogenic lines (NILs) confirmed a change in CESA4 expression that segregates within that interval. We sequenced the promoters and identified 16 polymorphisms differentiating CESA4^Sha and CESA4^Bay . In order to determine which of these SNPs could be responsible for this eQTL, we screened for transcription factor protein affinity with promoter fragments of CESA4^Bay, CESA4^Sha , and the reference genome CESA4^Col . The wall thickening activator proteins NAC SECONDARY WALL THICKENING PROMOTING FACTOR2 (NST2) and NST3 exhibited a decrease in binding with the CESA4^Sha promoter with a tracheary element-regulating cis-element (TERE) polymorphism. While NILs harboring the TERE polymorphisms exhibited significantly different CESA4 expression, cellulose crystallinity and cell wall thickness were indistinguishable. These results suggest that the TERE polymorphism resulted in differential transcription factor binding and CESA4 expression; yet A. thaliana is able to tolerate this transcriptional variability without compromising the structural elements of the plant, providing insight into the elasticity of gene regulation as it pertains to cell wall biosynthesis and regulation. We also explored available DNA affinity purification sequencing data to resolve a core binding site, C(G/T)TNNNNNNNA(A/C)G, for secondary wall NACs referred to as the VNS element.

Biomass and waste materials as potential sources of nanocrystalline cellulose: Comparative review of preparation methods (2016 - Till date)

Nanocrystalline cellulose (NCC) has gained much popularity over the last decade as a preferred nanomaterial in varied applications, despite its laborious industrial production and higher cost. Its production methods have undergone a great deal of metamorphosis lately. The main emphasis has been on the environment-friendly and green processes, in addition to the sustainable and renewable feedstock. Globally, the researchers have explored biomass and waste cellulosic materials as renewable sources for NCC extraction. Newer and/or improved process alternatives, e.g., ultrasonication, enzymatic hydrolysis and mechanical treatments have been applied successfully for producing high-quality material. Detailed investigations on optimizing the overall yield from cheaper feedstock have yielded obvious benefits. This is still work in progress. The present review majorly focuses on the advances made in the NCC preparation field from biomass and waste cellulosic materials in last three years (2016 - till date). Collaborative efforts between chemical engineers and research scientists are crucial for the success of this really amazing nanomaterial.