A high-affinity potassium transporter (MeHKT1) from cassava (Manihot esculenta) negatively regulates the response of transgenic Arabidopsis to salt stress.

BACKGROUND: High-affinity potassium transporters (HKTs) are crucial in facilitating potassium uptake by plants. Many types of HKTs confer salt tolerance to plants through regulating K+ and Na+ homeostasis under salinity stress. However, their specific functions in cassava (Manihot esculenta) remain unclear. RESULTS: Herein, an HKT gene (MeHKT1) was cloned from cassava, and its expression is triggered by exposure to salt stress. The expression of a plasma membrane-bound protein functions as transporter to rescue a low potassium (K+) sensitivity of yeast mutant strain, but the complementation of MeHKT1 is inhibited by NaCl treatment. Under low K+ stress, transgenic Arabidopsis with MeHKT1 exhibits improved growth due to increasing shoot K+ content. In contrast, transgenic Arabidopsis accumulates more Na+ under salt stress than wild-type (WT) plants. Nevertheless, the differences in K+ content between transgenic and WT plants are not significant. Additionally, Arabidopsis expressing MeHKT1 displayed a stronger salt-sensitive phenotype. CONCLUSION: These results suggest that under low K+ condition, MeHKT1 functions as a potassium transporter. In contrast, MeHKT1 mainly transports Na+ into cells under salt stress condition and negatively regulates the response of transgenic Arabidopsis to salt stress. Our results provide a reference for further research on the function of MeHKT1, and provide a basis for further application of MeHKT1 in cassava by molecular biological means.

Proline inhibits postharvest physiological deterioration of cassava by improving antioxidant capacity.

Cassava (Manihot esculenta Crantz), a crucial global tuber crop, encounters significant economic losses attributed to postharvest physiological deterioration (PPD). The PPD phenomenon in cassava is closely related to the accumulation of reactive oxygen species (ROS), and amino acids play a pivotal role in regulating signaling pathways and eliminating ROS. In this study, the storage performance of eight cassava varieties were conducted. Cassava cultivar SC5 showed the best storage performance among the eight cassava varieties, but the edible cassava cultivar SC9 performed much worse. Comparative analysis of free amino acids was conducted in eight cassava varieties, revealing changes in proline, aspartic acid, histidine, glutamic acid, threonine, and serine. Exogenous supplementation of these six amino acids was performed to inhibit PPD of SC9. Proline was confirmed as the key amino acid for inhibiting PPD. Treatment with optimal exogenous proline of 5 g/L resulted in a 17.9% decrease in the deterioration rate compared to untreated cassava. Accompanied by a decrease in H2O2 content and an increase in catalase, superoxide dismutase and ascorbate peroxidase activity. Proline treatment proved to be an effective approach to alleviate cell oxidative damage, inhibit PPD in cassava, and prolong shelf life.

Study on multiscale structures and digestibility of cassava starch and medium-chain fatty acids complexes using molecular simulation techniques.

Effect of complexation of three medium-chain fatty acids (octanoic, decylic and lauric acid, OA, DA and LA, respectively) on structural characteristics, physicochemical properties and digestion behaviors of cassava starch (CS) was investigated. Current study indicated that LA was more easily to combine with CS (complex index 88.9%), followed by DA (80.9%), which was also consistent with their corresponding complexed lipids content. Following the investigation of morphology, short-range ordered structure, helical structure, crystalline/amorphous region and fractal dimension of the various complexes, all cassava starch-fatty acids complexes (CS-FAs) were characterized with a flaked morphology rather than a round morphology in native starch (control CS). X-ray diffraction demonstrated that all CS-FAs had a V-type crystalline structure, and nuclear magnetic resonance spectroscopy confirmed that the complexes made from different fatty acids displayed similar V6 or V7 type polymorphs. Interestingly, small-angle X-ray scattering analysis revealed that α value became greater following increased carbon chain length of fatty acids, indicating the formation of a more ordered fractal structure in the aggregates. Changes in rheological parameters G' and G'' indicated that starch complexed with fatty acids was more likely to form a gel network, but difference among three CS-FAs complexes was significant, which might be contributed to their corresponding hydrophobicity and hydrophilicity raised from individual fatty acids. Importantly, digestion indicated that CS-LA complexes had the lowest hydrolysis degree, followed by the greatest RS content, indicating the importance of chain length of fatty acids for manipulating the fine structure and functionality of the complexes.

Functional Characterization of the MeSSIII-1 Gene and Its Promoter from Cassava.

Soluble starch synthases (SSs) play important roles in the synthesis of cassava starch. However, the expression characteristics of the cassava SSs genes have not been elucidated. In this study, the MeSSIII-1 gene and its promoter, from SC8 cassava cultivars, were respectively isolated by PCR amplification. MeSSIII-1 protein was localized to the chloroplasts. qRT-PCR analysis revealed that the MeSSIII-1 gene was expressed in almost all tissues tested, and the expression in mature leaves was 18.9 times more than that in tuber roots. MeSSIII-1 expression was induced by methyljasmonate (MeJA), abscisic acid (ABA), and ethylene (ET) hormones in cassava. MeSSIII-1 expression patterns were further confirmed in proMeSSIII-1 transgenic cassava. The promoter deletion analysis showed that the -264 bp to -1 bp MeSSIII-1 promoter has basal activity. The range from -1228 bp to -987 bp and -488 bp to -264 bp significantly enhance promoter activity. The regions from -987 bp to -747 bp and -747 bp to -488 bp have repressive activity. These findings will provide an important reference for research on the potential function and transcriptional regulation mechanisms of the MeSSIII-1 gene and for further in-depth exploration of the regulatory network of its internal functional elements.

Fractionation of cassava pectins and their detailed structural analyses using various pectinolytic enzymes.

In this study, we analyzed the pectin structure within the pulp of cassava. Cassava pectin, derived from cassava pulp treatment at 120 °C for 90 min, was separated into four fractions (CP-P, CP-SD1, CP-SD2F, and CP-SD2R) based on variations in water solubility, electrical properties, and molecular weights. Sugar composition analysis demonstrated an abundance of homogalacturonan (HG) in CP-P and CP-SD2F, rhamnogalacturonan I (RG-I) in CP-SD2R, and neutral sugars in CP-SD1. Because RG-I possesses a complex structure, we analyzed CP-SD2R using various pectinolytic enzymes. Galactose was the major sugar in CP-SD2R accounting for 49 %, of which 65 % originated from arabinogalactan I, 9 % from galactose and galactooligosaccharides, 5 % from arabinogalactan II, and 11 % from galactoarabinan. Seventy-four percent of arabinose in CP-SD2R was present as galactoarabinan. The methylation (DM) and acetylation (DAc) degrees of cassava pectin were 11 and 15 %, respectively. The HG and RG-I regions exhibited DAc values of 5 and 44 %, respectively, signifying the high DAc of RG-I compared to HG. Information derived from the structural analysis of cassava pectin will enable efficient degradation of pectin and cellulose, leading to the use of cassava pulp as a raw material for biorefineries.

KIN10-mediated HB16 protein phosphorylation and self-association improve cassava disease resistance by transcriptional activation of lignin biosynthesis genes.

Cassava bacterial blight significantly affects cassava yield worldwide, while major cassava cultivars are susceptible to this disease. Therefore, it is crucial to identify cassava disease resistance gene networks and defence molecules for the genetic improvement of cassava cultivars. In this study, we found that MeHB16 transcription factor as a differentially expressed gene in cassava cultivars with contrasting disease resistance, positively modulated disease resistance by modulating defence molecule lignin accumulation. Further investigation showed that MeHB16 physically interacted with itself via the leucine-Zippe domain (L-Zip), which was necessary for the transcriptional activation of downstream lignin biosynthesis genes. In addition, protein kinase MeKIN10 directly interacted with MeHB16 to promote its phosphorylation at Ser6, which in turn enhanced MeHB16 self-association and downstream lignin biosynthesis. In summary, this study revealed the molecular network of MeKIN10-mediated MeHB16 protein phosphorylation improved cassava bacterial blight resistance by fine-tuning lignin biosynthesis and provides candidate genes and the defence molecule for improving cassava disease resistance.

Comparative transcriptomics analysis reveals defense mechanisms of Manihot esculenta Crantz against Sri Lanka Cassava MosaicVirus.

BACKGROUND: Cassava mosaic disease (CMD), caused by Sri Lankan cassava mosaic virus (SLCMV) infection, has been identified as a major pernicious disease in Manihot esculenta Crantz (cassava) plantations. It is widespread in Southeast Asia, especially in Thailand, which is one of the main cassava supplier countries. With the aim of restricting the spread of SLCMV, we explored the gene expression of a tolerant cassava cultivar vs. a susceptible cassava cultivar from the perspective of transcriptional regulation and the mechanisms underlying plant immunity and adaptation. RESULTS: Transcriptomic analysis of SLCMV-infected tolerant (Kasetsart 50 [KU 50]) and susceptible (Rayong 11 [R 11]) cultivars at three infection stages-that is, at 21 days post-inoculation (dpi) (early/asymptomatic), 32 dpi (middle/recovery), and 67 dpi (late infection/late recovery)-identified 55,699 expressed genes. Differentially expressed genes (DEGs) between SLCMV-infected KU 50 and R 11 cultivars at (i) 21 dpi to 32 dpi (the early to middle stage), and (ii) 32 dpi to 67 dpi (the middle stage to late stage) were then identified and validated by real-time quantitative PCR (RT-qPCR). DEGs among different infection stages represent genes that respond to and regulate the viral infection during specific stages. The transcriptomic comparison between the tolerant and susceptible cultivars highlighted the role of gene expression regulation in tolerant and susceptible phenotypes. CONCLUSIONS: This study identified genes involved in epigenetic modification, transcription and transcription factor activities, plant defense and oxidative stress response, gene expression, hormone- and metabolite-related pathways, and translation and translational initiation activities, particularly in KU 50 which represented the tolerant cultivar in this study.

Effect of cassava pulp treated with Lactobacillus casei TH14, urea, and molasses on gas kinetics, rumen fermentation, and degradability using the in vitro gas technique.

This study focused on examining the gas dynamics, rumen fermentation, and digestibility of ensiled cassava pulp (CSVP) using Lactobacillus casei TH14, urea, and molasses in the context of a laboratory experiment. All data in this study were analyzed using treatments arranged in 2 × 2 × 2 factorial arrangements using a completely randomized design. The L.casei TH14 additive (L) was factor A. Factor B was the molasses additive (M), while factor C was urea (U). There was no interaction effect of L, U, and M on gas production, volatile fatty acid (VFA) content, pH value, or ammonia-nitrogen level (P<0.05). The interaction of L, U, and M influenced in vitro dry matter digestibility (IVDMD) at 12 h (P < 0.05), and the CSVP fermented with the additions of L, U, and M together (LUM) was higher than the additions of CON, M, U, UM, and L on IVDMD (P < 0.05). However, the IVDMD values of adding LUM were higher in the control group (CON), M, U, UM, and L additive groups (P < 0.05). There was an interaction effect of L, U, and M on the protozoal count at 8 h (P<0.05), which had a lower protozoal count in the control group. In addition, acetic acid and butyric acid concentrations at 4 h and 8 h (P<0.05) were increased during the fermentation of CSVP using L and M combinations. Furthermore, the combination of U and M enhanced (P<0.05) average acetic acid, propionic acid, and pH at 4 h and 8 h while reducing (P<0.05) the gas generation from the insoluble portion (b). It was suggested that utilizing L. casei TH14 together with urea and molasses can enhance nutrient contents and improve the in vitro dry matter digestibility of CSVP, although it has no effect on ruminal fermentation or gas production.

CRISPR/Cas9-generated mutations in a sugar transporter gene reduce cassava susceptibility to bacterial blight.

Bacteria from the genus Xanthomonas are prolific phytopathogens that elicit disease in over 400 plant species. Xanthomonads carry a repertoire of specialized proteins called transcription activator-like (TAL) effectors that promote disease and pathogen virulence by inducing expression of host susceptibility (S) genes. Xanthomonas phaseoli pv. manihotis (Xpm) causes bacterial blight on the staple food crop cassava (Manihot esculenta Crantz). The Xpm effector TAL20 induces ectopic expression of the S gene Manihot esculenta Sugars Will Eventually be Exported Transporter 10a (MeSWEET10a), which encodes a sugar transporter that contributes to cassava bacterial blight susceptibility. We used CRISPR/Cas9 to generate multiple cassava lines with edits to the MeSWEET10a TAL20 effector binding site and/or coding sequence. In several of the regenerated lines, MeSWEET10a expression was no longer induced by Xpm, and in these cases, we observed reduced cassava bacterial blight (CBB) disease symptoms post Xpm infection. Because MeSWEET10a is expressed in cassava flowers, we further characterized the reproductive capability of the MeSWEET10a promoter and coding sequence mutants. Lines were crossed to themselves and to wild-type plants. The results indicated that expression of MeSWEET10a in female, but not male, flowers, is critical to produce viable F1 seed. In the case of promoter mutations that left the coding sequence intact, viable F1 progeny were recovered. Taken together, these results demonstrate that blocking MeSWEET10a induction is a viable strategy for decreasing cassava susceptibility to CBB and that ideal lines will contain promoter mutations that block TAL effector binding while leaving endogenous expression of MeSWEET10a unaltered.

Occurrence of Cassava (Manihot esculenta) Leaf Spot Disease Caused by Diaporthe ueckeri in China.

Cassava (Manihot esculenta) is a perennial crop of the family Euphorbiaceae, widely cultivated due to its phytopharmacological and economic values in China. In November 2022, a leaf spot disease on cassava was observed in Zhanjiang, Guangdong, China (21.17° N, 110.18° E), with 100% disease incidence. About 80 % of leaves were covered with spots on the infected plants. Typical symptoms initially appeared as irregular water-soaked lesions that became brown and whitish with the progress of the disease, lesions gradually expanded and coalesced, causing leaf withering, drying and final fall. Tissues (4 to 5 mm) were excised from the margin of lesions, sterilized in 3% H2O2 solution for 3 min, rinsed three times with sterile water, placed on potato dextrose agar (PDA) medium (containing 50mg/L penicillin), and incubated at 25-28 °C. Ten single hypha isolates with similar morphology were obtained and further purified as single conidium subcultures. The colony was grey whitish with sparse aerial mycelium and colony diameter reached 70.4 mm after four days incubation at 25-28℃ in the dark. Black pycnidia occurring as clusters were spherical or irregular, erumpent at maturity, often with a creamy whitish, conidial cirrus extruding from ostiole after 30-days incubation. Conidiophores were hyaline, smooth, unbranched. Alpha conidia were bi-guttulate, hyaline, ellipsoidal, aseptate, with dimensions of 5.1~7.5×1.9~3.4µm (mean 6.2×2.8 µm, n>50). Beta conidia were abundant, filiform, hyaline, smooth, curved in a hooked shape, with a truncate base and dimensions of 18.5-26.4 × 0.6-1.2µm (mean 23.4 × 1.0 µm, n= 40) . Gamma conidia were not observed. The morphological characteristics were similar to those of Diaporthe ueckeri (Udayanga et al. 2015). The internal transcribed spacer (ITS) region, large subunit (LSU) rRNA sequence, actin (ACT), calmodulin (CAL), histone H3 (HIS), translation elongation factor 1-alpha (TEF1-α), and ß-tubulin (TUB) genes of a representative isolate CCAS-MS-6 (ACCC 35497) were amplified and sequenced using primer pairs: ITS5/ITS4, LR0R/LR5, ACT-512F/ACT-783R, CAL228F/CAL737R, CYLH3F/ H3-1b, EF1-728F/ EF1-986R and Bt2a/Bt2b (Gao et al 2017；Udayanga et al 2014). All sequences were deposited in GenBank (OR361671, OR361672, and OR365605-9). BLAST search showed high similarities with sequences of Diaporthe ueckeri (Tab 1). Maximum likelihood analyses of the concatenated data of CAL, HIS, ITS, TEF and TUB using Mega 11 placed CCAS-MS-6 in the D. ueckeri clade. Thus, the fungus was identified as D. ueckeri. Three one-year old healthy plants were used for pathogenicity tests in pots. Two 15-day old leaves of each plant were cleaned with 75% alcohol, three sites on each leaf were wounded, and sites on one of the leaf were covered with fungal plugs from 15-day-old cultures on PDA, and sites on the other leaf with PDA plugs as a control. All plants were kept at ambient temperature (about 28℃) and covered with plastic bags containing sterile wet cotton to maintain the humidity. Seven days after inoculation, all inoculated sites showed symptoms of necrosis, while control sites showed no symptoms. The same fungus identified on the basis of morphological and molecular criteria was reisolated from symptomatic inoculated leaves. In China, D. ueckeri had been reported to cause diseases on Eucalyptus citriodora, Camellia sinensis, and Michelia shiluensis (Gao et al 2016; Liao et al 2023; Yi et al 2018), this is the first report on M. esculenta. The definition of the disease etiology is a prerequisite to develop effective management strategies.

Cassava brown streak virus evolves with a nucleotide-substitution rate that is typical for the family Potyviridae.

The ipomoviruses (family Potyviridae) that cause cassava brown streak disease (cassava brown streak virus [CBSV] and Uganda cassava brown streak virus [UCBSV]) are damaging plant pathogens that affect the sustainability of cassava production in East and Central Africa. However, little is known about the rate at which the viruses evolve and when they emerged in Africa - which inform how easily these viruses can host shift and resist RNAi approaches for control. We present here the rates of evolution determined from the coat protein gene (CP) of CBSV (Temporal signal in a UCBSV dataset was not sufficient for comparable analysis). Our BEAST analysis estimated the CBSV CP evolves at a mean rate of 1.43 × 10-3 nucleotide substitutions per site per year, with the most recent common ancestor of sampled CBSV isolates existing in 1944 (95% HPD, between years 1922 - 1963). We compared the published measured and estimated rates of evolution of CPs from ten families of plant viruses and showed that CBSV is an average-evolving potyvirid, but that members of Potyviridae evolve more quickly than members of Virgaviridae and the single representatives of Betaflexiviridae, Bunyaviridae, Caulimoviridae and Closteroviridae.

Corrigendum: A promoter toolbox for tissue-specific expression supporting translational research in cassava (Manihot esculenta).

[This corrects the article DOI: 10.3389/fpls.2022.1042379.].

Genetic analysis of cassava brown streak disease root necrosis using image analysis and genome-wide association studies.

Cassava brown streak disease (CBSD) poses a substantial threat to food security. To address this challenge, we used PlantCV to extract CBSD root necrosis image traits from 320 clones, with an aim of identifying genomic regions through genome-wide association studies (GWAS) and candidate genes. Results revealed strong correlations among certain root necrosis image traits, such as necrotic area fraction and necrotic width fraction, as well as between the convex hull area of root necrosis and the percentage of necrosis. Low correlations were observed between CBSD scores obtained from the 1-5 scoring method and all root necrosis traits. Broad-sense heritability estimates of root necrosis image traits ranged from low to moderate, with the highest estimate of 0.42 observed for the percentage of necrosis, while narrow-sense heritability consistently remained low, ranging from 0.03 to 0.22. Leveraging data from 30,750 SNPs obtained through DArT genotyping, eight SNPs on chromosomes 1, 7, and 11 were identified and associated with both the ellipse eccentricity of root necrosis and the percentage of necrosis through GWAS. Candidate gene analysis in the 172.2kb region on the chromosome 1 revealed 24 potential genes with diverse functions, including ubiquitin-protein ligase, DNA-binding transcription factors, and RNA metabolism protein, among others. Despite our initial expectation that image analysis objectivity would yield better heritability estimates and stronger genomic associations than the 1-5 scoring method, the results were unexpectedly lower. Further research is needed to comprehensively understand the genetic basis of these traits and their relevance to cassava breeding and disease management.

Cassava pomace-based biodegradable packaging materials: a review.

Starch-based biodegradable packaging materials are gaining popularity as an alternative to the adverse environmental effects caused by conventional packaging materials. Despite the fact that cassava can withstand harsh environmental conditions and convert a greater quantity of solar energy into carbohydrates, its postharvest shelf life is extremely short. The preparation of cassava starch is an important method for extending the storage life of cassava. When one ton of cassava is processed, approximately 900 kg of cassava pomace, also known as cassava bagasse and cassava pulp, are produced. Due to the high residual starch and fibre content, reinforced packaging materials made from cassava pomace predominate. In the present manuscript, many possible uses of cassava pomace in packaging materials are discussed.  Furthermore, the performance attributes of packing materials assume a crucial role in the evaluation of the quality of the respective materials. The manuscript discusses various performance characteristics of packaging materials derived from cassava pomace. The features discussed include water vapour permeability, moisture content, solubility, thickness, colour, light barrier properties, mechanical properties, FT-IR analysis, thermal stability, biodegradation, contact angle, and the presence of plasticizers. Though cassava starch film has become a favourable substitute for conventional packaging materials, commercialization is limited due to having drawbacks, and the current solutions are also catalogued in this review.

Green Synthesis of Ceria Nanoparticles from Cassava Tubers for Electrochemical Aptasensor Detection of SARS-CoV-2 on a Screen-Printed Carbon Electrode.

Green synthesis approaches for making nanosized ceria using starch from cassava as template molecules to control the particle size are reported. The results of the green synthesis of ceria with an optimum calcination temperature of 800 °C shows a size distribution of each particle of less than 30 nm with an average size of 9.68 nm, while the ratio of Ce3+ to Ce4+ was 25.6%. The green-synthesized nanoceria are applied to increase the sensitivity and attach biomolecules to the electrode surface of the electrochemical aptasensor system for coronavirus disease (COVID-19). The response of the aptasensor to the receptor binding domain of the virus was determined with the potassium ferricyanide redox system. The screen-printed carbon electrode that has been modified with green-synthesized nanoceria shows 1.43 times higher conductivity than the bare electrode, while those modified with commercial ceria increase only 1.18 times. Using an optimized parameter for preparing the aptasensors, the detection and quantification limits were 1.94 and 5.87 ng·mL-1, and the accuracy and precision values were 98.5 and 89.1%. These results show that green-synthesized ceria could be a promising approach for fabricating an electrochemical aptasensor.

Positive Regulatory Roles of Manihot esculenta HAK5 under K+ Deficiency or High Salt Stress.

HAK/KUP/KT family members have been identified as playing key roles in K+ uptake and salt tolerance in numerous higher plants. However, their functions in cassava (Manihot esculenta Cantz) remain unknown. In this study, a gene encoding for a high-affinity potassium transporter (MeHAK5) was isolated from cassava and its function was investigated. Subcellular localization analysis showed that MeHAK5 is a plasma membrane-localized transporter. RT-PCR and RT-qPCR indicated that MeHAK5 is predominantly expressed in cassava roots, where it is upregulated by low potassium or high salt; in particular, its highest expression levels separately increased by 2.2 and 2.9 times after 50 µM KCl and 150 mM NaCl treatments. When heterologously expressed in yeast, MeHAK5 mediated K+ uptake within the cells of the yeast strain CY162 and rescued the salt-sensitive phenotype of AXT3K yeast. MeHAK5 overexpression in transgenic Arabidopsis plants exhibited improved growth and increased shoot K+ content under low potassium conditions. Under salt stress, MeHAK5 transgenic Arabidopsis plants accumulated more K+ in the shoots and roots and had reduced Na+ content in the shoots. As a result, MeHAK5 transgenic Arabidopsis demonstrated a more salt-tolerant phenotype. These results suggest that MeHAK5 functions as a high-affinity K+ transporter under K+ starvation conditions, improving K+/Na+ homeostasis and thereby functioning as a positive regulator of salt stress tolerance in transgenic Arabidopsis. Therefore, MeHAK5 may be a suitable candidate gene for improving K+ utilization efficiency and salt tolerance.

NF-YC15 transcription factor activates ethylene biosynthesis and improves cassava disease resistance.

The nuclear factor Y (NF-Y) transcription factors play important roles in plant development and physiological responses. However, the relationship between NF-Y, plant hormone and plant stress resistance in tropical crops remains unclear. In this study, we identified MeNF-YC15 gene in the NF-Y family that significantly responded to Xanthomonas axonopodis pv. manihotis (Xam) treatment. Using MeNF-YC15-silenced and -overexpressed cassava plants, we elucidated that MeNF-YC15 positively regulated disease resistance to cassava bacterial blight (CBB). Notably, we illustrated MeNF-YC15 downstream genes and revealed the direct genetic relationship between MeNF-YC15 and 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (MeACO1)-ethylene module in disease resistance, as evidenced by the rescued disease susceptibility of MeNF-YC15 silenced cassava plants with ethylene treatment or overexpressing MeACO1. In addition, the physical interaction between 2C-type protein phosphatase 1 (MePP2C1) and MeNF-YC15 inhibited the transcriptional activation of MeACO1 by MeNF-YC15. In summary, MePP2C1-MeNF-YC15 interaction modulates ethylene biosynthesis and cassava disease resistance, providing gene network for cassava genetic improvement.

Resistance to Cassava Whitefly (Bemisia tabaci) among Eastern and Southern African Elite Cassava Genotypes.

Cassava whitefly, Bemisia tabaci, directly damages cassava leaves by feeding on phloem, causing chlorosis and abscission, leading to a yield loss of up to 50%. The pest also causes indirect damage through sooty mold formation. Most Ugandan cassava varieties resist cassava mosaic disease (CMD) and tolerate cassava brown streak disease (CBSD), but little is known about their response to whitefly infestation. The main objective of this study was to identify cassava genotypes with putative resistance to whitefly in Uganda. This was conducted on 24 improved cassava varieties in three agro-ecological zones during the second rains of 2016. Monthly data were taken for adult and nymph counts, whitefly and sooty mold damage, and CMD and CBSD severities from 2 to 9 months after planting (MAPs). The results show that the whitefly population is highly significantly (p < 0.000) amongst varieties across the three agro-ecological zones. Mkumba consistently supported the low adult numbers and nymphs. The findings demonstrate the potential of the improved cassava varieties as sources of whitefly resistance for sustainable management.

RNA splicing modulates the postharvest physiological deterioration of cassava storage root.

Rapid postharvest physiological deterioration (PPD) of cassava (Manihot esculenta Crantz) storage roots is a major constraint that limits the potential of this plant as a food and industrial crop. Extensive studies have been performed to explore the regulatory mechanisms underlying the PPD processes in cassava to understand their molecular and physiological responses. However, the exceptional functional versatility of alternative splicing (AS) remains to be explored during the PPD process in cassava. Here, we identified several aberrantly spliced genes during the early PPD stage. An in-depth analysis of AS revealed that the abscisic acid (ABA) biosynthesis pathway might serve as an additional molecular layer in attenuating the onset of PPD. Exogenous ABA application alleviated PPD symptoms through maintaining ROS generation and scavenging. Interestingly, the intron retention transcript of MeABA1 (ABA DEFICIENT 1) was highly correlated with PPD symptoms in cassava storage roots. RNA yeast three-hybrid and RNA immunoprecipitation assays showed that the serine/arginine-rich protein MeSCL33 (SC35-like splicing factor 33) binds to the precursor mRNA of MeABA1. Importantly, overexpressing MeSCL33 in cassava conferred improved PPD resistance by manipulating the AS and expression levels of MeABA1 and then modulating the endogenous ABA levels in cassava storage roots. Our results uncovered the pivotal role of the ABA biosynthesis pathway and RNA splicing in regulating cassava PPD resistance and proposed the essential roles of MeSCL33 for conferring PPD resistance, broadening our understanding of SR proteins in cassava development and stress responses.

Novel SNP markers and other stress-related genomic regions associated with nitrogen use efficiency in cassava.

Cassava productivity is constrained by low soil nitrogen, which is predominant in most cassava-growing regions in the tropics and subtropical agroecology. Improving the low nitrogen tolerance of cassava has become an important breeding objective. The current study aimed to develop cassava varieties with improved nitrogen use efficiency by identifying genomic regions and candidate genes linked to nitrogen use efficiency in cassava. A genome-wide association study (GWAS) was performed using the Genome Association and Prediction Integrated Tool (GAPIT). A panel of 265 diverse cassava genotypes was phenotyped for 10 physiological and agronomic traits under optimum and low-nitrogen regimes. Whole-genome genotyping of these cassava cloneswas performed using the Diversity Arrays Technology (DArTseq) sequencing platform. A total of 68,814 single nucleotide polymorphisms (SNPs) were identified, which were spread across the entire 18 chromosomes of the cassava genome, of which 52 SNPs at various densities were found to be associated with nitrogen use efficiency in cassava and other yield-related traits. The putative genes identified through GWAS, especially those with significant associated SNP markers for NUE and related traits have the potential, if deployed appropriately, to develop cassava varieties with improved nitrogen use efficiency, which would translate to a reduction in the economic and environmental cost of cassava production.