Singleton mutations in large-scale cancer genome studies: uncovering the tail of cancer genome.

Singleton or low-frequency driver mutations are challenging to identify. We present a domain driver mutation estimator (DOME) to identify rare candidate driver mutations. DOME analyzes positions analogous to known statistical hotspots and resistant mutations in combination with their functional and biochemical residue context as determined by protein structures and somatic mutation propensity within conserved PFAM domains, integrating the CADD scoring scheme. Benchmarked against seven other tools, DOME exhibited superior or comparable accuracy compared to all evaluated tools in the prediction of functional cancer drivers, with the exception of one tool. DOME identified a unique set of 32 917 high-confidence predicted driver mutations from the analysis of whole proteome missense variants within domain boundaries across 1331 genes, including 1192 noncancer gene census genes, emphasizing its unique place in cancer genome analysis. Additionally, analysis of 8799 TCGA (The Cancer Genome Atlas) and in-house tumor samples revealed 847 potential driver mutations, with mutations in tyrosine kinase members forming the dominant burden, underscoring its higher significance in cancer. Overall, DOME complements current approaches for identifying novel, low-frequency drivers and resistant mutations in personalized therapy.

Association mapping reveals novel genes and genomic regions controlling grain size architecture in mini core accessions of Indian National Genebank wheat germplasm collection.

Wheat (Triticum aestivum L.) is a staple food crop for the global human population, and thus wheat breeders are consistently working to enhance its yield worldwide. In this study, we utilized a sub-set of Indian wheat mini core germplasm to underpin the genetic architecture for seed shape-associated traits. The wheat mini core subset (125 accessions) was genotyped using 35K SNP array and evaluated for grain shape traits such as grain length (GL), grain width (GW), grain length, width ratio (GLWR), and thousand grain weight (TGW) across the seven different environments (E1, E2, E3, E4, E5, E5, E6, and E7). Marker-trait associations were determined using a multi-locus random-SNP-effect Mixed Linear Model (mrMLM) program. A total of 160 non-redundant quantitative trait nucleotides (QTNs) were identified for four grain shape traits using two or more GWAS models. Among these 160 QTNs, 27, 36, 38, and 35 QTNs were associated for GL, GW, GLWR, and TGW respectively while 24 QTNs were associated with more than one trait. Of these 160 QTNs, 73 were detected in two or more environments and were considered reliable QTLs for the respective traits. A total of 135 associated QTNs were annotated and located within the genes, including ABC transporter, Cytochrome450, Thioredoxin_M-type, and hypothetical proteins. Furthermore, the expression pattern of annotated QTNs demonstrated that only 122 were differentially expressed, suggesting these could potentially be related to seed development. The genomic regions/candidate genes for grain size traits identified in the present study represent valuable genomic resources that can potentially be utilized in the markers-assisted breeding programs to develop high-yielding varieties.

Genome wide identification of MADS box gene family in Musa balbisiana and their divergence during evolution.

MADS box gene family is transcription factor gene family that is involved in growth and development of eukaryotes. In plants the MADS box gene family is mainly associated with floral meristem identity and flower development, apart from being involved in nearly all the phases of plant growth. The MADS box gene family has also been shown to be involved during fruit development and ripening. In this study the MADS box gene family from Musa balbisiana was identified and the divergence of this gene family between Musa balbisiana and Musa acuminata studied. A total of 97 MADS box genes were identified from the genome of Musa balbisiana. Phylogenetic analysis showed that the MbMADS box genes were categorised into type I (α and γ; the ß group was not distinguishable) and type II groups (MIKCc and MIKC* and MIKCc was further divided into 13 subfamilies). The typeII group has the largest number of genes and also showed the most expansion which could be correlated with the whole genome duplications. There were significant differences in the MADS box genes from Musa acuminata and Musa balbisiana during evolution that can be correlated with different floral phenotype and fruit ripening pattern. The divergence of the MADS RIN genes in Musa balbisiana as compared to Musa acuminata might play an important role in the slow ripening of Musa balbisiana fruits.

Analysis of the Rdr1 gene family in different Rosaceae genomes reveals an origin of an R-gene cluster after the split of Rubeae within the Rosoideae subfamily.

The Rdr1 gene confers resistance to black spot in roses and belongs to a large TNL gene family, which is organized in two major clusters at the distal end of chromosome 1. We used the recently available chromosome scale assemblies for the R. chinensis 'Old Blush' genome, re-sequencing data for nine rose species and genome data for Fragaria, Rubus, Malus and Prunus to identify Rdr1 homologs from different taxa within Rosaceae. Members of the Rdr1 gene family are organized into two major clusters in R. chinensis and at a syntenic location in the Fragaria genome. Phylogenetic analysis indicates that the two clusters existed prior to the split of Rosa and Fragaria and that one cluster has a more recent origin than the other. Genes belonging to cluster 2, such as the functional Rdr1 gene muRdr1A, were subject to a faster evolution than genes from cluster 1. As no Rdr1 homologs were found in syntenic positions for Prunus persica, Malus x domestica and Rubus occidentalis, a translocation of the Rdr1 clusters to the current positions probably happened after the Rubeae split from other groups within the Rosoideae approximately 70-80 million years ago during the Cretaceous period.

Genome-wide identification and interactome analysis of members of two-component system in Banana.

BACKGROUND: Ethylene signal transduction in plants is conducted by the two-component system (TCS) which consists of histidine kinase (HK), histidine phosphotransferase (HPT) and response regulators (RRs). This system plays an important role in signal transduction during various cellular processes, including fruit ripening and response to multiple environmental cues. Though members of TCS have been identified in a few plants, no detailed analysis has been carried out in banana. RESULTS: Through genome-wide analysis, we identified a total of 80 (25 HK, 10 HPT and 45 RR) and 72 (25 HK, 5 HPT and 42 RR) TCS genes in Musa acuminata and Musa balbisiana respectively. The analysis of identified genes revealed that most of the genes are highly conserved however; there are subtle divergences among various members. Comparative expression analysis revealed an involvement of a set of TCS members during banana fruit ripening. Co-expression network analysis identified a working TCS module with direct interactions of HK-HPT and RR members. The molecular dynamics analysis of TCS module showed a significant change in structural trajectories of TCS proteins in the presence of ethylene. Analysis suggests possible interactions between the HK-HPTs and RRs as well as other members leading to banana fruit ripening. CONCLUSIONS: In this study, we identified and compared the members of TCS gene family in two banana species and showed their diversity, within groups on the basis of whole-genome duplication events. Our analysis showed that during banana fruit ripening TCS module plays a crucial role. We also demonstrated a possible interaction mechanism of TCS proteins in the presence and absence of ethylene by molecular dynamics simulations. These findings will help in understanding the functional mechanism of TCS proteins in plants in different conditions.

Differential transcriptome modulation leads to variation in arsenic stress response in Arabidopsis thaliana accessions.

Arsenic (As) is a ubiquitous metalloid and a health hazard to millions of people worldwide. The presence of As in groundwater poses a threat as it not only affects crop productivity but also contaminates food chain. Therefore, it is essential to understand molecular mechanisms underlying uptake, transport and accumulation of As in plants. In recent past, natural variation in Arabidopsis thaliana has been utilized to understand molecular and genetic adaptation under different stresses. In this study, responses of Arabidopsis accessions were analyzed at biochemical and molecular levels towards arsenate [As(V)] stress. On the basis of reduction in root length, accessions were categorized into tolerant and sensitive ones towards As(V). Root length analysis led to the identification of Col-0 (<10% reduction) and Slavi-1 (>60% reduction) as the most tolerant and sensitive accessions, respectively. Comparative genome-wide expression analysis revealed differential expression of 168 and 548 genes in Col-0 and Slavi-1, respectively, with 120 common differentially expressed genes. A number of genes associated with defense and stress-response, transport system, regulatory mechanisms and biochemical processes showed differential expression in contrasting accessions. The study provides an insight into the molecular mechanisms associated with stress response and processes involved in adaptation strategies towards As stress.

Transcriptome and metabolite analyses in Azadirachta indica: identification of genes involved in biosynthesis of bioactive triterpenoids.

Azadirachta indica A. Juss, commonly known as Neem, is the reservoir of triterpenoids of economic importance. Metabolite analysis of different developmental stages of leaf and fruit suggests tissue-specific accumulation of the major triterpenoids in this important tree. Though biosynthesis of these complex molecules requires substrate flux from the isoprenoid pathway, enzymes involved in late biosynthetic steps remain uncharacterized. We established and analyzed transcriptome datasets from leaf and fruit and identified members of gene families involved in intermediate steps of terpenoid backbone biosynthesis and those related to secondary transformation leading to the tissue-specific triterpenoid biosynthesis. Expression analysis suggests differential expression of number of genes between leaf and fruit and probable participation in the biosynthesis of fruit-specific triterpenoids. Genome-wide analysis also identified members of gene families putatively involved in secondary modifications in late biosynthetic steps leading to the synthesis of highly oxygenated triterpenoids. Expression and molecular docking analyses suggest involvement of specific members of CYP450 family in secondary modifications for the biosynthesis of bioactive triterpenoids. This study generated rich genomic resource and identified genes involved in biosynthesis of important molecules, which will aid in the advancement of tools for functional genomics and elucidation of the biosynthesis of triterpenoid from this important tree.

Simulated herbivory in chickpea causes rapid changes in defense pathways and hormonal transcription networks of JA/ethylene/GA/auxin within minutes of wounding.

Chickpea (C. arietinum L.) is an important pulse crop in Asian and African countries that suffers significant yield losses due to attacks by insects like H. armigera. To obtain insights into early responses of chickpea to insect attack, a transcriptomic analysis of chickpea leaves just 20 minutes after simulated herbivory was performed, using oral secretions of H. armigera coupled with mechanical wounding. Expression profiles revealed differential regulation of 8.4% of the total leaf transcriptome with 1334 genes up-regulated and 501 down-regulated upon wounding at log2-fold change (|FC| ≤ -1 and ≥1) and FDR value ≤ 0.05. In silico analysis showed the activation of defenses through up-regulation of genes of the phenylpropanoid pathway, pathogenesis, oxidases and CYTP450 besides differential regulation of kinases, phosphatases and transcription factors of the WRKY, MYB, ERFs, bZIP families. A substantial change in the regulation of hormonal networks was observed with up-regulation of JA and ethylene pathways and suppression of growth associated hormone pathways like GA and auxin within 20 minutes of wounding. Secondary qPCR comparison of selected genes showed that oral secretions often increased differential expression relative to mechanical damage alone. The studies provide new insights into early wound responses in chickpea.

Genome-wide Expression Analysis and Metabolite Profiling Elucidate Transcriptional Regulation of Flavonoid Biosynthesis and Modulation under Abiotic Stresses in Banana.

Flavonoid biosynthesis is largely regulated at the transcriptional level due to the modulated expression of genes related to the phenylpropanoid pathway in plants. Although accumulation of different flavonoids has been reported in banana, a staple fruit crop, no detailed information is available on regulation of the biosynthesis in this important plant. We carried out genome-wide analysis of banana (Musa acuminata, AAA genome) and identified 28 genes belonging to 9 gene families associated with flavonoid biosynthesis. Expression analysis suggested spatial and temporal regulation of the identified genes in different tissues of banana. Analysis revealed enhanced expression of genes related to flavonol and proanthocyanidin (PA) biosynthesis in peel and pulp at the early developmental stages of fruit. Genes involved in anthocyanin biosynthesis were highly expressed during banana fruit ripening. In general, higher accumulation of metabolites was observed in the peel as compared to pulp tissue. A correlation between expression of genes and metabolite content was observed at the early stage of fruit development. Furthermore, this study also suggests regulation of flavonoid biosynthesis, at transcriptional level, under light and dark exposures as well as methyl jasmonate (MJ) treatment in banana.

Genome-Wide Identification and Expression Analysis of Homeodomain Leucine Zipper Subfamily IV (HDZ IV) Gene Family from Musa accuminata.

The homeodomain zipper family (HD-ZIP) of transcription factors is present only in plants and plays important role in the regulation of plant-specific processes. The subfamily IV of HDZ transcription factors (HD-ZIP IV) has primarily been implicated in the regulation of epidermal structure development. Though this gene family is present in all lineages of land plants, members of this gene family have not been identified in banana, which is one of the major staple fruit crops. In the present work, we identified 21 HDZIV encoding genes in banana by the computational analysis of banana genome resource. Our analysis suggested that these genes putatively encode proteins having all the characteristic domains of HDZIV transcription factors. The phylogenetic analysis of the banana HDZIV family genes further confirmed that after separation from a common ancestor, the banana, and poales lineages might have followed distinct evolutionary paths. Further, we conclude that segmental duplication played a major role in the evolution of banana HDZIV encoding genes. All the identified banana HDZIV genes expresses in different banana tissue, however at varying levels. The transcript levels of some of the banana HDZIV genes were also detected in banana fruit pulp, suggesting their putative role in fruit attributes. A large number of genes of this family showed modulated expression under drought and salinity stress. Taken together, the present work lays a foundation for elucidation of functional aspects of the banana HDZIV encoding genes and for their possible use in the banana improvement programs.

Genome-wide analysis of the AP2/ERF family in Musa species reveals divergence and neofunctionalisation during evolution.

AP2/ERF domain containing transcription factor super family is one of the important regulators in the plant kingdom. The involvement of AP2/ERF family members has been elucidated in various processes associated with plant growth, development as well as in response to hormones, biotic and abiotic stresses. In this study, we carried out genome-wide analysis to identify members of AP2/ERF family in Musa acuminata (A genome) and Musa balbisiana (B genome) and changes leading to neofunctionalisation of genes. Analysis identified 265 and 318 AP2/ERF encoding genes in M. acuminata and M. balbisiana respectively which were further classified into ERF, DREB, AP2, RAV and Soloist groups. Comparative analysis indicated that AP2/ERF family has undergone duplication, loss and divergence during evolution and speciation of the Musa A and B genomes. We identified nine genes which are up-regulated during fruit ripening and might be components of the regulatory machinery operating during ethylene-dependent ripening in banana. Tissue-specific expression analysis of the genes suggests that different regulatory mechanisms might be involved in peel and pulp ripening process through recruiting specific ERFs in these tissues. Analysis also suggests that MaRAV-6 and MaERF026 have structurally diverged from their M. balbisiana counterparts and have attained new functions during ripening.

Comparative analysis of transcription factor gene families from Papaver somniferum: identification of regulatory factors involved in benzylisoquinoline alkaloid biosynthesis.

Opium poppy (Papaver somniferum L.), known for biosynthesis of several therapeutically important benzylisoquinoline alkaloids (BIAs), has emerged as the premier organism to study plant alkaloid metabolism. The most prominent molecules produced in opium poppy include narcotic analgesic morphine, the cough suppressant codeine, the muscle relaxant papaverine and the anti-microbial agent sanguinarine and berberine. Despite several health benefits, biosynthesis of some of these molecules is very low due to tight temporal and spatial regulation of the genes committed to their biosynthesis. Transcription factors, one of the prime regulators of secondary plant product biosynthesis, might be involved in controlled biosynthesis of BIAs in P. somniferum. In this study, identification of members of different transcription factor gene families using transcriptome datasets of 10 cultivars of P. somniferum with distinct chemoprofile has been carried out. Analysis suggests that most represented transcription factor gene family in all the poppy cultivars is WRKY. Comparative transcriptome analysis revealed differential expression pattern of the members of a set of transcription factor gene families among 10 cultivars. Through analysis, two members of WRKY and one member of C3H gene family were identified as potential candidates which might regulate thebaine and papaverine biosynthesis, respectively, in poppy.

Differential expression of microRNAs by arsenate and arsenite stress in natural accessions of rice.

Arsenic (As) contamination of rice (Oryza sativa) imposes a serious threat to human health worldwide. Understanding the molecular mechanisms of As transport and accumulation in rice may provide promising solutions to the problem. MicroRNAs (miRNAs) are a novel class of short, endogenous, non-coding small RNA molecules involved in a wide variety of biological processes such as organ polarity, morphogenesis, floral transition, hormone signalling and adaptation to environment. In the past, a few studies led to the identification of differentially expressed miRNAs in rice in response to arsenite (As(III)) stress. However, studies related to differential miRNA expression involving natural rice accessions exposed to different species of As have not been carried out. Such studies are required to identify As-species responsive miRNAs in different rice accessions. In this study, we have carried out miRNA profiling in contrasting As accumulating rice accessions using miRNA Array. We report identification of differentially expressed miRNAs in contrasting As accumulating rice cultivars in response to As(III) (25 µM) and As(v) (50 µM) stress. A significant up-regulation in expression was observed among members of the miR396, miR399, miR408, miR528, miR1861, miR2102 and miR2907 families in response to As(III) and As(v) stress in both cultivars. In addition, members of the miR164, miR171, miR395, miR529, miR820, miR1432 and miR1846 families were down-regulated. The differentially expressed miRNAs were subjected to validation of expression and bioinformatic analyses to predict and categorise the key miRNAs and their target genes involved in As stress. Analysis suggests that As-species and rice accession specific miRNA might be responsible for the differential response of contrasting rice accessions towards As(III) and As(v) stress. Study of the proximal promoter sequences of the As-responsive miRNAs suggests that these identified miRNAs contain metal-responsive cis-acting motifs and other elicitor and hormonal related motifs. Our study suggests a miRNA-dependent regulatory mechanism during As species-specific stress in different rice accessions. Further analysis based on results obtained will be helpful in dissecting the molecular mechanism behind As responses in different rice accessions.

Transcriptome analysis of ripe and unripe fruit tissue of banana identifies major metabolic networks involved in fruit ripening process.

BACKGROUND: Banana is one of the most important crop plants grown in the tropics and sub-tropics. It is a climacteric fruit and undergoes ethylene dependent ripening. Once ripening is initiated, it proceeds at a fast rate making postharvest life short, which can result in heavy economic losses. During the fruit ripening process a number of physiological and biochemical changes take place and thousands of genes from various metabolic pathways are recruited to produce a ripe and edible fruit. To better understand the underlying mechanism of ripening, we undertook a study to evaluate global changes in the transcriptome of the fruit during the ripening process. RESULTS: We sequenced the transcriptomes of the unripe and ripe stages of banana (Musa accuminata; Dwarf Cavendish) fruit. The transcriptomes were sequenced using a 454 GSFLX-Titanium platform that resulted in more than 7,00,000 high quality (HQ) reads. The assembly of the reads resulted in 19,410 contigs and 92,823 singletons. A large number of the differentially expressed genes identified were linked to ripening dependent processes including ethylene biosynthesis, perception and signalling, cell wall degradation and production of aromatic volatiles. In the banana fruit transcriptomes, we found transcripts included in 120 pathways described in the KEGG database for rice. The members of the expansin and xyloglucan transglycosylase/hydrolase (XTH) gene families were highly up-regulated during ripening, which suggests that they might play important roles in the softening of the fruit. Several genes involved in the synthesis of aromatic volatiles and members of transcription factor families previously reported to be involved in ripening were also identified. CONCLUSIONS: A large number of differentially regulated genes were identified during banana fruit ripening. Many of these are associated with cell wall degradation and synthesis of aromatic volatiles. A large number of differentially expressed genes did not align with any of the databases and might be novel genes in banana. These genes can be good candidates for future studies to establish their role in banana fruit ripening. The datasets developed in this study will help in developing strategies to manipulate banana fruit ripening and reduce post harvest losses.

Heavy metals induce oxidative stress and genome-wide modulation in transcriptome of rice root.

Industrial growth, ecological disturbances and agricultural practices have contaminated the soil and water with many harmful compounds, including heavy metals. These heavy metals affect growth and development of plants as well as cause severe human health hazards through food chain contamination. In past, studies have been made to identify biochemical and molecular networks associated with heavy metal toxicity and uptake in plants. Studies suggested that most of the physiological and molecular processes affected by different heavy metals are similar to those affected by other abiotic stresses. To identify common and unique responses by different metals, we have studied biochemical and genome-wide modulation in transcriptome of rice (IR-64 cultivar) root after exposure to cadmium (Cd), arsenate [As(V)], lead (Pb) and chromium [Cr(VI)] in hydroponic condition. We observed that root tissue shows variable responses for antioxidant enzyme system for different heavy metals. Genome-wide expression analysis suggests variable number of genes differentially expressed in root in response to As(V), Cd, Pb and Cr(VI) stresses. In addition to unique genes, each heavy metal modulated expression of a large number of common genes. Study also identified cis-acting regions of the promoters which can be determinants for the modulated expression of the genes in response to different heavy metals. Our study advances understanding related to various processes and networks which might be responsible for heavy metal stresses, accumulation and detoxification.

Genome-wide identification and expression analysis of the mitogen-activated protein kinase gene family from banana suggest involvement of specific members in different stages of fruit ripening.

Mitogen-activated protein kinases (MAPKs) are important components of the tripartite mitogen-activated protein kinase signaling cascade and play an important role in plant growth and development. Although members of the MAPK gene family have been identified in model plants, little information is available regarding this gene family in fruit crops. In this study, we carried out a computational analysis using the Musa Genome database to identify members of the MAPK gene family in banana, an economically important crop and the most popular fruit worldwide. Our analysis identified 25 members of the MAP kinase (MAPK or MPK) gene family. Phylogenetic analyses of MPKs in Arabidopsis, Oryza, and Populus have classified these MPKs into four subgroups. The presence of conserved domains in the deduced amino acid sequences, phylogeny, and genomic organization strongly support their identity as members of the MPK gene family. Expression analysis during ethylene-induced banana fruit ripening suggests the involvement of several MPKs in the ethylene signal transduction pathway that are necessary for banana fruit ripening. Analysis of the cis-regulatory elements in the promoter regions and the involvement of the identified MPKs in various cellular processes, as analyzed using Pathway Studio, suggest a role for the banana MPK gene family in diverse functions related to growth, development, and the stress response. This report is the first concerning the identification of members of a gene family and the elucidation of their role in various processes using the Musa Genome database.

Large-scale resource development in Gossypium hirsutum L. by 454 sequencing of genic-enriched libraries from six diverse genotypes.

The sequence information has been proved to be an essential genomic resource in case of crop plants for their genetic improvement and better utilization by humans. To dissect the Gossypium hirsutum genome for large-scale development of genomic resources, we adopted hypomethylated restriction-based genomic enrichment strategy to sequence six diverse genotypes. Approximately 5.2-Gb data (more than 18.36 million reads) was generated which, after assembly, represents nearly 1.27-Gb genomic sequences. We predicted a total of 93,363 gene models (21,399 full length) and identified 35,923 gene models which were validated against already sequenced plant genomes. A total of 1,093 transcription factor-encoding genes, 3,135 promoter sequences and 78 miRNA (including 17 newly identified in Gossypium) were predicted. We identified significant no. of molecular markers including 47,093 novel simple sequence repeats and 66,364 novel single nucleotide polymorphisms. In addition, we developed NBRI-Comprehensive Cotton Genomics database, a web resource to provide access of cotton-related genomic resources developed at NBRI. This study contributes considerable amount of genomic resources and suggests a potential role of genic-enriched sequencing in genomic resource development for orphan crop plants.

Comparative transcriptome analysis using high papaverine mutant of Papaver somniferum reveals pathway and uncharacterized steps of papaverine biosynthesis.

The benzylisoquinoline alkaloid papaverine, synthesized in low amount in most of the opium poppy varieties of Papaver somniferum, is used as a vasodilator muscle relaxant and antispasmodic. Papaverine biosynthesis remains controversial as two different routes utilizing either (S)-coclaurine or (S)-reticuline have been proposed with uncharacterized intermediate steps. In an attempt to elucidate papaverine biosynthesis and identify putative genes involved in uncharacterized steps, we carried out comparative transcriptome analysis of high papaverine mutant (pap1) and normal cultivar (BR086) of P. somniferum. This natural mutant synthesizes more than 12-fold papaverine in comparison to BR086. We established more than 238 Mb transcriptome data separately for pap1 and BR086. Assembly of reads generated 127,342 and 106,128 unigenes in pap1 and BR086, respectively. Digital gene expression analysis of transcriptomes revealed 3,336 differentially expressing unigenes. Enhanced expression of (S)-norcoclaurine-6-O-methyltransferase (6OMT), (S)-3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase (4'OMT), norreticuline 7-O-methyltransferase (N7OMT) and down-regulation of reticuline 7-O-methyltransferase (7OMT) in pap1 in comparison to BR086 suggest (S)-coclaurine as the route for papaverine biosynthesis. We also identified several methyltransferases and dehydrogenases with enhanced expression in pap1 in comparison to BR086. Our analysis using natural mutant, pap1, concludes that (S)-coclaurine is the branch-point intermediate and preferred route for papaverine biosynthesis. Differentially expressing methyltransferases and dehydrogenases identified in this study will help in elucidating complete biosynthetic pathway of papaverine. The information generated will be helpful in developing strategies for enhanced biosynthesis of papaverine through biotechnological approaches.

Comparative transcriptomic analysis of roots of contrasting Gossypium herbaceum genotypes revealing adaptation to drought.

BACKGROUND: Root length and its architecture govern the adaptability of plants to various stress conditions, including drought stress. Genetic variations in root growth, length, and architecture are genotypes dependent. In this study, we compared the drought-induced transcriptome of four genotypes of Gossypium herbaceum that differed in their drought tolerance adaptability. Three different methodologies, namely, microarray, pyrosequencing, and qRT-PCR, were used for transcriptome analysis and validation. RESULTS: The variations in root length and growth were found among four genotypes of G.herbaceum when exposed to mannitol-induced osmotic stress. Under osmotic stress, the drought tolerant genotypes Vagad and GujCot-21 showed a longer root length than did by drought sensitive RAHS-14 and RAHS-IPS-187. Further, the gene expression patterns in the root tissue of all genotypes were analyzed. We obtained a total of 794 differentially expressed genes by microarray and 104928 high-quality reads representing 53195 unigenes from the root transcriptome. The Vagad and GujCot-21 respond to water stress by inducing various genes and pathways such as response to stresses, response to water deprivation, and flavonoid pathways. Some key regulatory genes involved in abiotic stress such as AP2 EREBP, MYB, WRKY, ERF, ERD9, and LEA were highly expressed in Vagad and GujCot-21. The genes RHD3, NAP1, LBD, and transcription factor WRKY75, known for root development under various stress conditions, were expressed specifically in Vagad and GujCot-21. The genes related to peroxidases, transporters, cell wall-modifying enzymes, and compatible solutes (amino acids, amino sugars, betaine, sugars, or sugar alcohols) were also highly expressed in Vagad and Gujcot-21. CONCLUSION: Our analysis highlights changes in the expression pattern of genes and depicts a small but highly specific set of drought responsive genes induced in response to drought stress. Some of these genes were very likely to be involved in drought stress signaling and adaptation, such as transmembrane nitrate transporter, alcohol dehydrogenase, pyruvate decarboxylase, sucrose synthase, and LEA. These results might serve as the basis for an in-depth genomics study of Gossypium herbaceum, including a comparative transcriptome analysis and the selection of genes for root traits and drought tolerance.