Stress In Cassava Research Articles

Dynamic DNA methylation modifications in the cold stress response of cassava

Cassava, a crucial tropical crop, faces challenges from cold stress, necessitating an exploration of its molecular response. Here, we investigated the role of DNA methylation in moderating the response to moderate cold stress (10 °C) in cassava. Using whole-genome bisulfite sequencing, we examined DNA methylation patterns in leaf blades and petioles under control conditions, 5 h, and 48 h of cold stress. Tissue-specific responses were observed, with leaf blades exhibiting subtle changes, while petioles displayed a pronounced decrease in methylation levels under cold stress. We identified cold stress-induced differentially methylated regions (DMRs) that demonstrated both tissue and treatment specificity. Importantly, these DMRs were enriched in genes with altered expression, implying functional relevance. The cold-response transcription factor ERF105 associated with DMRs emerged as a significant and conserved regulator across tissues and treatments. Furthermore, we investigated DNA methylation dynamics in transposable elements, emphasizing the sensitivity of MITEs with bHLH binding motifs to cold stress. These findings provide insights into the epigenetic regulation of response to cold stress in cassava, contributing to an understanding of the molecular mechanisms underlying stress adaptation in this tropical plant.

MeSWEET15a/b genes play a role in the resistance of cassava (Manihot esculenta Crantz) to water and salt stress by modulating sugar distribution

The sugar transporter SWEET plays a role in plant growth, carbon allocation, and abiotic stress resistance. We examined the function of SWEET in cassava (Manihot esculenta Crantz) under water and salt stress. Bioinformatics, subcellular localization, yeast deficient complementation, and virus-induced gene silencing (VIGS) were used to examine the function of SWEET in cassava. Twenty-eight MeSWEETs genes were found based on the conserved domain MtN3/saliva of SWEET transporters, two MeSWEET15a/b of them were identified by phylogenetic analysis, which were located on the cell membrane. They transfer sucrose, fructose, glucose, and mannitol from culture media to yeast cells, predominately transferring sucrose via bleeding fluid saps in plant. Leaf sucrose content was increased in MeSWEET15a/b-silenced cassava plants, resulting in changes in carbon distribution, with an increase in starch accumulation in the leaves and a decrease in starch accumulation in the roots. The silencing of MeSWEET15a/b genes led to tolerance to water and salt stress, consistent with a high accumulation of osmolytes, and low lipid membrane peroxidation. Changes in sugar distribution increased the expression of MeTOR and MeE2Fa in pTRV2-MeSWEET15a and pTRV2-MeSWEET15b cassava leaves. MeSWEET15a/b acts as pivotal modulators of sugar distribution and tolerance to water and high salt stress in cassava.

Cell signaling during drought and/or cold stress in cassava

Cassava (<italic>Manihot esculenta</italic> Crantz) is a root crop significant in food security and various bio-industrial applications such as animal feed, modified starch, and biofuels. Drought and cold stress are two major factors limiting cassava production qualitatively and quantitatively, for which plants have evolved mechanisms to overcome the impact of these two stressors. In recent years, significant progress has been achieved in understanding the response mechanism of cassava plants to stress signals to tolerate the above stresses. In this review, core stress-signaling pathways, including transcription factor (TF)-related regulatory networks, plant hormone signaling, reactive oxygen species (ROS) scavenging, and non-coding RNA (ncRNA) and alternative splicing (AS) that modify gene expression levels in response to drought and/or cold stress in cassava, are summarized. Understanding these stress signaling and responses will increase our ability to improve the crops tolerance to multiple stresses for agricultural sustainability and food security for the growing world population.

Large-scale RNAseq analysis reveals new insights into the key genes and regulatory networks of anthocyanin biosynthesis during development and stress in cassava

Anthocyanins play key roles in plant development and response to various biotic and abiotic stresses including drought, cold, and pathogens. However, the key genes and regulatory networks relevant to anthocyanin biosynthesis remain largely elusive in cassava (Manihot esculenta L.), an important starchy root crop in tropical and sub-tropical regions. In this study, 465 RNAseq data were gathered to construct gene coexpression networks in cassava, resulting in a total of 30 coexpression modules (M1-M30). The associations of module-tissue or module-stress/development were systematically analyzed. Meanwhile, the hub genes and molecular roles were extensively dissected for each module, respectively. Notably, module M5 was significantly enriched in phenylpropanoid and flavonoid metabolisms, and several crucial genes participating in anthocyanin biosynthesis were included, suggesting a major role of M5 in anthocyanin biosynthesis in cassava. Coexpression analyses further revealed that phenylalanine ammonia-lyase 1 (PAL1), anthocyanidin synthase (ANS), and flavanone 3-hydroxylase (F3H) were the hub genes with most connections to others. Four transcription factors and three cis-regulatory motifs which might involve in anthocyanin biosynthesis regulation were also explored. Finally, a conserved coexpression network, covering the entire pathway of anthocyanin biosynthesis, was revealed among cassava, Arabidopsis thaliana (L.), and rice (Oryza sativa L.). The results provide valuable information to the key genes and regulatory networks of anthocyanin biosynthesis, and also lay a useful foundation for the genetic improvement in cassava.

Genetically Different Isolates of the Arbuscular Mycorrhizal Fungus Rhizophagus irregularis Induce Differential Responses to Stress in Cassava.

Water scarcity negatively impacts global crop yields and climate change is expected to greatly increase the severity of future droughts. The use of arbuscular mycorrhizal fungi (AMF) can potentially mitigate the effects of water stress in plants. Cassava is a crop that feeds approximately 800 million people daily. Genetically different isolates of the AMF R. irregularis as well as their clonal progeny have both been shown to greatly alter cassava growth in field conditions. Given that cassava experiences seasonal drought in many of the regions in which it is cultivated, we evaluated whether intraspecific variation in R. irregularis differentially alters physiological responses of cassava to water stress. In a first experiment, conducted in field conditions in Western Kenya, cassava was inoculated with two genetically different R. irregularis isolates and their clonal progeny. All cassava plants exhibited physiological signs of stress during the dry period, but the largest differences occurred among plants inoculated with clonal progeny of each of the two parental fungal isolates. Because drought had not been experimentally manipulated in the field, we conducted a second experiment in the greenhouse where cassava was inoculated with two genetically different R. irregularis isolates and subjected to drought, followed by re-watering, to allow recovery. Physiological stress responses of cassava to drought differed significantly between plants inoculated with the two different fungi. However, plants that experienced higher drought stress also recovered at a faster rate following re-watering. We conclude that intraspecific genetic variability in AMF significantly influences cassava physiological responses during water stress. This highlights the potential of using naturally existing variation in AMF to improve cassava tolerance undergoing water stress. However, the fact that clonal progeny of an AMF isolate can differentially affect how cassava copes with natural drought stress in field conditions, highlights the necessity to understand additional factors, beyond genetic variation, which can account for such large differences in cassava responses to drought.

In silico cloning and bioinformatics analysis of HSP21 in Manihot esculenta

HSP21 gene is a key gene to respond high temperature stress in plant and plays an important role in preventing protein denaturation, protecting cell structure and maintaining normal growth and development. Therefore, cloning HSP21 gene is the basis for revealing the molecular mechanism of resistance to high temperature stress in cassava. To obtain cassava HSP21 homologous gene and analyze the properties of predicted protein, electronic cloning technology was used to assemble and derivate new gene in this study, and bioinformatics analysis method was used to analyze the primary to highest structure, hydrophilicity/hydrophobicity, signal peptide, protein homology and phylogenetic evolution of expressed protein. HSP21 gene was 969 bp, its open reading frame was 705 bp, and the predicted protein contains 234 amino acids. The predicted protein is a non-transmembrane protein that is alkaline and hydrophilic, and is mainly localized in the chloroplast. Through multiple sequence alignment and phylogenetic analysis, it was found that the cassava HSP21 protein has high homology with other plants such as Hevea brasiliensis, Ricinus communis, and Jatropha curcas. The results could provide reference for the study of cloning and transformation of this gene.

Melatonin synthesis enzymes interact with ascorbate peroxidase to protect against oxidative stress in cassava

Melatonin is an important indole amine hormone in animals and plants. The enzymes that catalyse melatonin synthesis positively regulate plant stress responses through modulation of the accumulation of reactive oxygen species (ROS). However, the relationship between melatonin biosynthetic enzymes and ROS-scavenging enzymes has not been characterized. In this study, we demonstrate that two enzymes of the melatonin synthesis pathway in Manihot esculenta (MeTDC2 and MeASMT2) directly interact with ascorbate peroxidase (MeAPX2) in both in vitro and in vivo experiments. Notably, in the presence of MeTDC2 and MeASMT2, MeAPX2 showed significantly higher activity and antioxidant capacity than the purified MeAPX2 protein alone. These findings indicate that MeTDC2-MeAPX2 and MeASMT2-MeAPX2 interactions both activate APX activity and increase antioxidant capacity. In addition, the combination of MeTDC2, MeASMT2, and MeAPX2 conferred improved resistance to hydrogen peroxide in Escherichia coli. Moreover, this combination also positively regulates oxidative stress tolerance in cassava. Taken together, these findings not only reveal a direct interaction between MeTDC2, MeASMT2, and MeAPX2, but also highlight the importance of this interaction in regulating redox homoeostasis and stress tolerance in cassava.

Involvement of abscisic acid-responsive element-binding factors in cassava (Manihot esculenta) dehydration stress response

Cassava (Manihot esculenta) is a major staple food, animal feed and energy crop in the tropics and subtropics. It is one of the most drought-tolerant crops, however, the mechanisms of cassava drought tolerance remain unclear. Abscisic acid (ABA)-responsive element (ABRE)-binding factors (ABFs) are transcription factors that regulate expression of target genes involved in plant tolerance to drought, high salinity, and osmotic stress by binding ABRE cis-elements in the promoter regions of these genes. However, there is little information about ABF genes in cassava. A comprehensive analysis of Manihot esculenta ABFs (MeABFs) described the phylogeny, genome location, cis-acting elements, expression profiles, and regulatory relationship between these factors and Manihot esculenta betaine aldehyde dehydrogenase genes (MeBADHs). Here we conducted genome-wide searches and subsequent molecular cloning to identify seven MeABFs that are distributed unevenly across six chromosomes in cassava. These MeABFs can be clustered into three groups according to their phylogenetic relationships to their Arabidopsis (Arabidopsis thaliana) counterparts. Analysis of the 5′-upstream region of MeABFs revealed putative cis-acting elements related to hormone signaling, stress, light, and circadian clock. MeABF expression profiles displayed clear differences among leaf, stem, root, and tuberous root tissues under non-stress and drought, osmotic, or salt stress conditions. Drought stress in cassava leaves and roots, osmotic stress in tuberous roots, and salt stress in stems induced expression of the highest number of MeABFs showing significantly elevated expression. The glycine betaine (GB) content of cassava leaves also was elevated after drought, osmotic, or salt stress treatments. BADH1 is involved in GB synthesis. We show that MeBADH1 promoter sequences contained ABREs and that MeBADH1 expression correlated with MeABF expression profiles in cassava leaves after the three stress treatments. Taken together, these results suggest that in response to various dehydration stresses, MeABFs in cassava may activate transcriptional expression of MeBADH1 by binding the MeBADH1 promoter that in turn promotes GB biosynthesis and accumulation via an increase in MeBADH1 gene expression levels and MeBADH1 enzymatic activity. These responses protect cells against dehydration stresses by preserving an osmotic balance that enhances cassava tolerance to dehydration stresses.

The chloroplast proteome response to drought stress in cassava leaves

Cassava is an important tropical crop with strong resistance to drought stress. The chloroplast, the site of photosynthesis, is sensitive to stress, and the drought-response proteins in cassava chloroplasts are worthy of investigation. In this study, cassava leaves were collected for ultra-structure observation from plants subjected to different drought stress conditions. Our results showed that drought stress can promote starch accumulation in cassava chloroplasts. To evaluate changes in chloroplast proteins under different drought conditions, two-dimensional electrophoresis was performed using purified chloroplasts, which resulted in the identification of 26 unique chloroplast proteins responsive to drought stress. These drought-responsive proteins are predominantly related to photosynthesis, carbon and nitrogen metabolism, and amino acid metabolism. Among them, most photosynthesis-related proteins are downregulated, with decreases in photosynthetic parameters upon drought stress. Several proteins associated with carbon and nitrogen metabolism, including rubisco and carbonic anhydrase, were upregulated, which might promote drought tolerance in cassava by enhancing the carbohydrate conversion efficiency and protecting the plant from oxidative stress. Our proteomic data not only provide insight into the complement of proteins in cassava chloroplasts but also further our overall understanding of drought-responsive proteins in cassava chloroplasts.

MeABL5, an ABA Insensitive 5-Like Basic Leucine Zipper Transcription Factor, Positively Regulates MeCWINV3 in Cassava (Manihot esculenta Crantz).

The basic leucine zipper (bZIP) transcription factor family plays crucial roles in multiple biological processes, especially stress responses. Cassava (Manihot esculenta Crantz) is an important tropical crop with a strong tolerance to environmental stresses such as drought, heat, and low-fertility environments. Currently, limited information is available regarding the functional identification of bZIP transcription factors in response to abiotic stress in cassava. Herein, a gene encoding an ABA Insensitive 5 (ABI5)-like transcription factor, designated as MeABL5, was identified in cassava. Sequence and phylogenetic analysis showed that MeABL5 is a cassava bZIP transcription factor that is not included in the previously identified cassava bZIP family members, belongs to subfamily A, and has high sequence similarity to ABI5-like proteins. Subcellular localization and transactivation assays revealed that MeABL5 was a nuclear-localized protein and possessed transactivation activity. Furthermore, MeABL5 was able to specifically interact with the ABRE cis-element in the promoter of the cassava major cell wall invertase gene, MeCWINV3, in vitro and in vivo. MeABL5 and MeCWINV3 exhibited similar expression patterns in various organs or tissues and under abiotic stress in cassava. The expressions of MeABL5 and MeCWINV3 within cassava plantlets were both induced by exogenous abscisic acid (ABA), gibberellic acid (GA3), methyl jasmonate (MeJA), and heat. Overexpression of MeABL5 increased the activity of the MeCWINV3 gene, and the up-regulated expressions of MeCWINV3 were significantly activated under ABA-, salicylic acid (SA)-, and MeJA-induced conditions. Overall, these results suggest that MeABL5 is a positive regulator of MeCWINV3 and might participate in the robust resistance of cassava in response to abiotic stress. This study also provides a foundation for further research on ABA-mediated and stress-related signaling pathways in cassava.

Comparative physiology and transcriptome analysis allows for identification of lncRNAs imparting tolerance to drought stress in autotetraploid cassava

BackgroundPolyploidization, pervasive among higher plant species, enhances adaptation to water deficit, but the physiological and molecular advantages need to be investigated widely. Long non-coding RNAs (lncRNAs) are involved in drought tolerance in various crops.ResultsHerein, we demonstrate that tetraploidy potentiates tolerance to drought stress in cassava (Manihot esculenta Crantz). Autotetraploidy reduces transpiration by lesser extent increasing of stomatal density, smaller stomatal aperture size, or greater stomatal closure, and reducing accumulation of H2O2 under drought stress. Transcriptome analysis of autotetraploid samples revealed down-regulation of genes involved in photosynthesis under drought stress, and less down-regulation of subtilisin-like proteases involved in increasing stomatal density. UDP-glucosyltransferases were increased more or reduced less in dehydrated leaves of autotetraploids compared with controls. Strand-specific RNA-seq data (validated by quantitative real time PCR) identified 2372 lncRNAs, and 86 autotetraploid-specific lncRNAs were differentially expressed in stressed leaves. The co-expressed network analysis indicated that LNC_001148 and LNC_000160 in autotetraploid dehydrated leaves regulated six genes encoding subtilisin-like protease above mentioned, thereby result in increasing the stomatal density to a lesser extent in autotetraploid cassava. Trans-regulatory network analysis suggested that autotetraploid-specific differentially expressed lncRNAs were associated with galactose metabolism, pentose phosphate pathway and brassinosteroid biosynthesis, etc.ConclusionTetraploidy potentiates tolerance to drought stress in cassava, and LNC_001148 and LNC_000160 mediate drought tolerance by regulating stomatal density in autotetraploid cassava.

Strand-specific RNA-seq based identification and functional prediction of lncRNAs in response to melatonin and simulated drought stresses in cassava

Melatonin (MT) plays important roles in mediating plant responses to abiotic stresses such as drought. lncRNAs also play crucial roles in regulating responses to drought stress, however, their roles in MT-mediated drought stress responses in plants remain largely unknown. In this study, a total of 1405 high-confidence lncRNAs were identified in leaves of cassava, an important food crop in tropical and sub-tropical regions, using strand-specific RNA-seq technology. Of which, 185 were differentially expressed between polyethylene glycol (PEG) or MT treatment and the control condition. Trans-regulatory co-expression network revealed that MT-uniquely-responsive lncRNAs were mainly involved in tetrapyrrole synthesis, cytochrome P450, and cell wall modification; PEG-uniquely-responsive lncRNAs mainly participated in RNA regulation of transcription, calcium signaling, mitochondrial electron transport/ATP synthesis, hormone metabolism, and transport; and MT and PEG both-responsive lncRNAs were mainly involved in light reaction, light signaling, FA synthesis and FA elongation, secondary metabolism, and tetrapyrrole synthesis. In addition, 28 lncRNA-mRNA pairs referred to cis-acting regulation were identified, and these lncRNAs regulated the expression of their neighboring genes mainly through calcium signaling, RNA regulation of transcription, ABA and ethylene metabolism, and redox homeostasis. Besides, 78 lncRNAs (especially TCONS_00003360, TCONS_00015102, and TCONS_00149293) responsive to MT and/or PEG treatment were identified as putative targets of cassava known miRNAs. These findings provide a comprehensive view of the lncRNAs and their roles in response to MT and drought stress in cassava, which will enable in-depth functional analyses in the near future.

The Late Embryogenesis Abundant Protein Family in Cassava (Manihot esculenta Crantz): Genome-Wide Characterization and Expression during Abiotic Stress.

Late embryogenesis abundant (LEA) proteins, as a highly diverse group of polypeptides, play an important role in plant adaptation to abiotic stress; however, LEAs from cassava have not been studied in cassava. In this study, 26 LEA members were genome-wide identified from cassava, which were clustered into seven subfamily according to evolutionary relationship, protein motif, and gene structure analyses. Chromosomal location and duplication event analyses suggested that 26 MeLEAs distributed in 10 chromosomes and 11 MeLEA paralogues were subjected to purifying selection. Transcriptomic analysis showed the expression profiles of MeLEAs in different tissues of stem, leaves, and storage roots of three accessions. Comparative transcriptomic analysis revealed that the function of MeLEAs in response to drought may be differentiated in different accessions. Compared with the wild subspecies W14, more MeLEA genes were activated in cultivated varieties Arg7 and SC124 after drought treatment. Several MeLEA genes showed induction under various stresses and related signaling treatments. Taken together, this study demonstrates the transcriptional control of MeLEAs in tissue development and the responses to abiotic stress in cassava and identifies candidate genes for improving crop resistance to abiotic stress.

Genome-Wide Identification and Expression Analysis of the KUP Family under Abiotic Stress in Cassava (Manihot esculenta Crantz).

KT/HAK/KUP (KUP) family is responsible for potassium ion (K+) transport, which plays a vital role in the response of plants to abiotic stress by maintaining osmotic balance. However, our understanding of the functions of the KUP family in the drought-resistant crop cassava (Manihot esculenta Crantz) is limited. In the present study, 21 cassava KUP genes (MeKUPs) were identified and classified into four clusters based on phylogenetic relationships, conserved motifs, and gene structure analyses. Transcriptome analysis revealed the expression diversity of cassava KUPs in various tissues of three genotypes. Comparative transcriptome analysis showed that the activation of MeKUP genes by drought was more in roots than that in leaves of Arg7 and W14 genotypes, whereas less in roots than that in leaves of SC124 variety. These findings indicate that different cassava genotypes utilize various drought resistance mechanism mediated by KUP genes. Specific KUP genes showed broad upregulation after exposure to salt, osmotic, cold, H2O2, and abscisic acid (ABA) treatments. Taken together, this study provides insights into the KUP-mediated drought response of cassava at transcription levels and identifies candidate genes that may be utilized in improving crop tolerance to abiotic stress.

Farmers\u2019 knowledge and perception of postharvest physiological deterioration in cassava storage roots in Ghana

BackgroundIn spite of the essential role of cassava in ensuring household food security and employment for most rural farm households, postharvest physiological deterioration (PPD) of the roots which is serious abiotic stress in cassava renders the roots unmarketable, thereby reducing the economic value of the crop. This paper investigates farmers’ knowledge and perception of PPD in the storage roots of cassava among smallholders in Ghana.MethodsA participatory rural appraisal and a formal survey involving 137 farmers across four agro-ecological zones were conducted using focus group discussion and semi-structured questionnaires, respectively. With the appropriate perception indices, farmers’ perceptions of each PPD attribute were assessed by the use of a 5-point Likert scale. The Kendall’s coefficient of concordance was used further to rank identified cassava production constraints.ResultsThe result shows that a significant number of farmers were aware of PPD and the corresponding changes in the roots. It was also confirmed that PPD commences from 2 to 3 days after harvest. Farmers perceived PPD to be caused by pathogens, sunlight, mechanical injuries during harvesting and atmospheric air. The results further indicated that farmers have in-depth knowledge of PPD in cassava. The findings suggest the importance of PPD which is ranked as one of the major constraints in cassava production with about 40% agreement among the farmers. Storing of cassava roots in polythene and jute sacks were found to delay PPD for a few days.ConclusionThere is the need to concert cassava research and development efforts to tap into, and investigate further the adaptability and sustainability of these storage practices and methods to minimize both PPD and deterioration of cassava roots during storage.

Genome-wide characterization and expression profiling of HD-Zip gene family related to abiotic stress in cassava.

Homeodomain-leucine zipper (HD-Zip) gene family plays important roles in various abiotic stresses and hormone signaling in plants. However, no information is currently available regarding this family in cassava (Manihot esculenta), an important drought-tolerant crop in tropical and sub-tropical areas. Here, 57 HD-Zip genes (MeHDZ01-57) were identified in the cassava genome, and they were classified into four subfamilies based on phylogenetic analysis, which was further supported by their gene structure and conserved motif characteristics. Of which five gene pairs were involved in segmental duplication but none for tandem duplication, suggesting that segmental duplication was the main cause for the expansion of MeHDZ gene family in cassava. Global expression profiles revealed that MeHDZ genes were constitutively expressed, or not expressed, or tissue-specific expressed in examined tissues in both cultivated and wild subspecies. Transcriptomic analysis of three genotypes showed that most of MeHDZ genes responded differently to drought and polyethylene glycol treatments. Subsequently, quantitative RT-PCR analysis revealed comprehensive responses of twelve selected MeHDZ genes to various stimuli including cold, salt, and ABA treatments. These findings will increase our understanding of HD-Zip gene family involved in abiotic stresses and signaling transduction, and will provide a solid base for further functional characterization of MeHDZ genes in cassava.

The Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid Alleviates Salinity Stress in Cassava.

Cassava (Manihot esculenta Crantz) demand has been rising because of its various applications. High salinity stress is a major environmental factor that interferes with normal plant growth and limits crop productivity. As well as genetic engineering to enhance stress tolerance, the use of small molecules is considered as an alternative methodology to modify plants with desired traits. The effectiveness of histone deacetylase (HDAC) inhibitors for increasing tolerance to salinity stress has recently been reported. Here we use the HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA), to enhance tolerance to high salinity in cassava. Immunoblotting analysis reveals that SAHA treatment induces strong hyper-acetylation of histones H3 and H4 in roots, suggesting that SAHA functions as the HDAC inhibitor in cassava. Consistent with increased tolerance to salt stress under SAHA treatment, reduced Na+ content and increased K+/Na+ ratio were detected in SAHA-treated plants. Transcriptome analysis to discover mechanisms underlying salinity stress tolerance mediated through SAHA treatment reveals that SAHA enhances the expression of 421 genes in roots under normal condition, and 745 genes at 2 h and 268 genes at 24 h under both SAHA and NaCl treatment. The mRNA expression of genes, involved in phytohormone [abscisic acid (ABA), jasmonic acid (JA), ethylene, and gibberellin] biosynthesis pathways, is up-regulated after high salinity treatment in SAHA-pretreated roots. Among them, an allene oxide cyclase (MeAOC4) involved in a crucial step of JA biosynthesis is strongly up-regulated by SAHA treatment under salinity stress conditions, implying that JA pathway might contribute to increasing salinity tolerance by SAHA treatment. Our results suggest that epigenetic manipulation might enhance tolerance to high salinity stress in cassava.

Genome-wide characterization and analysis of bZIP transcription factor gene family related to abiotic stress in cassava.

The basic leucine zipper (bZIP) transcription factor family plays crucial roles in various aspects of biological processes. Currently, no information is available regarding the bZIP family in the important tropical crop cassava. Herein, 77 bZIP genes were identified from cassava. Evolutionary analysis indicated that MebZIPs could be divided into 10 subfamilies, which was further supported by conserved motif and gene structure analyses. Global expression analysis suggested that MebZIPs showed similar or distinct expression patterns in different tissues between cultivated variety and wild subspecies. Transcriptome analysis of three cassava genotypes revealed that many MebZIP genes were activated by drought in the root of W14 subspecies, indicating the involvement of these genes in the strong resistance of cassava to drought. Expression analysis of selected MebZIP genes in response to osmotic, salt, cold, ABA, and H2O2 suggested that they might participate in distinct signaling pathways. Our systematic analysis of MebZIPs reveals constitutive, tissue-specific and abiotic stress-responsive candidate MebZIP genes for further functional characterization in planta, yields new insights into transcriptional regulation of MebZIP genes, and lays a foundation for understanding of bZIP-mediated abiotic stress response.

Physiological Investigation and Transcriptome Analysis of Polyethylene Glycol (PEG)-Induced Dehydration Stress in Cassava.

Cassava is an important tropical and sub-tropical root crop that is adapted to drought environment. However, severe drought stress significantly influences biomass accumulation and starchy root production. The mechanism underlying drought-tolerance remains obscure in cassava. In this study, changes of physiological characters and gene transcriptome profiles were investigated under dehydration stress simulated by polyethylene glycol (PEG) treatments. Five traits, including peroxidase (POD) activity, proline content, malondialdehyde (MDA), soluble sugar and soluble protein, were all dramatically induced in response to PEG treatment. RNA-seq analysis revealed a gradient decrease of differentially expressed (DE) gene number in tissues from bottom to top of a plant, suggesting that cassava root has a quicker response and more induced/depressed DE genes than leaves in response to drought. Overall, dynamic changes of gene expression profiles in cassava root and leaves were uncovered: genes related to glycolysis, abscisic acid and ethylene biosynthesis, lipid metabolism, protein degradation, and second metabolism of flavonoids were significantly induced, while genes associated with cell cycle/organization, cell wall synthesis and degradation, DNA synthesis and chromatin structure, protein synthesis, light reaction of photosynthesis, gibberelin pathways and abiotic stress were greatly depressed. Finally, novel pathways in ABA-dependent and ABA-independent regulatory networks underlying PEG-induced dehydration response in cassava were detected, and the RNA-Seq results of a subset of fifteen genes were confirmed by real-time PCR. The findings will improve our understanding of the mechanism related to dehydration stress-tolerance in cassava and will provide useful candidate genes for breeding of cassava varieties better adapted to drought environment.

Reactive oxygen species regulate leaf pulvinus abscission zone cell separation in response to water-deficit stress in cassava.

Cassava (Manihot esculenta Crantz) plant resists water-deficit stress by shedding leaves leading to adaptive water-deficit condition. Transcriptomic, physiological, cellular, molecular, metabolic, and transgenic methods were used to study the mechanism of cassava abscission zone (AZ) cell separation under water-deficit stress. Microscopic observation indicated that AZ cell separation initiated at the later stages during water-deficit stress. Transcriptome profiling of AZ suggested that differential expression genes of AZ under stress mainly participate in reactive oxygen species (ROS) pathway. The key genes involved in hydrogen peroxide biosynthesis and metabolism showed significantly higher expression levels in AZ than non-separating tissues adjacent to the AZ under stress. Significantly higher levels of hydrogen peroxide correlated with hydrogen peroxide biosynthesis related genes and AZ cell separation was detected by microscopic observation, colorimetric detection and GC-MS analyses under stress. Co-overexpression of the ROS-scavenging proteins SOD and CAT1 in cassava decreased the levels of hydrogen peroxide in AZ under water-deficit stress. The cell separation of the pulvinus AZ also delayed in co-overexpression of the ROS-scavenging proteins SOD and CAT1 plants both in vitro and at the plant level. Together, the results indicated that ROS play an important regulatory role in the process of cassava leaf abscission under water-deficit stress.