The AT-hook motif nuclear-localized (AHL) family is pivotal for the abiotic stress response in plants. However, the function of the cassava AHL genes has not been elucidated. Promoters, as important regulatory elements of gene expression, play a crucial role in stress resistance. In this study, the promoter of the cassava MeAHL31 gene was cloned. The MeAHL31 protein was localized to the cytoplasm and the nucleus. qRT-PCR analysis revealed that the MeAHL31 gene was expressed in almost all tissues tested, and the expression in tuber roots was 321.3 times higher than that in petioles. Promoter analysis showed that the MeAHL31 promoter contains drought, methyl jasmonate (MeJA), abscisic acid (ABA), and gibberellin (GA) cis-acting elements. Expression analysis indicated that the MeAHL31 gene is dramatically affected by treatments with salt, drought, MeJA, ABA, and GA3. Histochemical staining in the proMeAHL31-GUS transgenic Arabidopsis corroborated that the GUS staining was found in most tissues and organs, excluding seeds. Beta-glucuronidase (GUS) activity assays showed that the activities in the proMeAHL31-GUS transgenic Arabidopsis were enhanced by different concentrations of NaCl, mannitol (for simulating drought), and MeJA treatments. The integrated findings suggest that the MeAHL31 promoter responds to the abiotic stresses of salt and drought, and its activity is regulated by the MeJA hormone signal.

BACKGROUND: Cassava is one of three major potato crops and the sixth most important food crop globally. Improving yield remains a primary aim in cassava breeding. Notably, plant height significantly impacts the yield and quality of crops; however, the mechanisms underlying cassava plant height development are yet to be elucidated.
RESULTS: In this study, we investigated the mechanisms responsible for cassava plant height development using phenotypic, anatomical, and transcriptomic analyses. Phenotypic and anatomical analysis revealed that compared to the high-stem cassava cultivar, the dwarf-stem cassava cultivar exhibited a significant reduction in plant height and a notable increase in internode tissue xylem area. Meanwhile, physiological analysis demonstrated that the lignin content of dwarf cassava was significantly higher than that of high cassava. Notably, transcriptome analysis of internode tissues identified several differentially expressed genes involved in cell wall synthesis and expansion, plant hormone signal transduction, phenylpropanoid biosynthesis, and flavonoid biosynthesis between the two cassava cultivars.
CONCLUSIONS: Our findings suggest that internode tissue cell division, secondary wall lignification, and hormone-related gene expression play important roles in cassava plant height development. Ultimately, this study provides new insights into the mechanisms of plant height morphogenesis in cassava and identifies candidate regulatory genes associated with plant height that can serve as valuable genetic resources for future crop dwarfing breeding.

Drought presents a significant abiotic stress that threatens crop productivity worldwide. Rhizosphere bacteria play pivotal roles in modulating plant growth and resilience to environmental stresses. Despite this, the extent to which rhizosphere bacteria are instrumental in plant responses to drought, and whether distinct cassava (Manihot esculenta Crantz) varieties harbor specific rhizosphere bacterial assemblages, remains unclear. In this study, we measured the growth and physiological characteristics, as well as the physical and chemical properties of the rhizosphere soil of drought-tolerant (SC124) and drought-sensitive (SC8) cassava varieties under conditions of both well-watered and drought stress. Employing 16S rDNA high-throughput sequencing, we analyzed the composition and dynamics of the rhizosphere bacterial community. Under drought stress, biomass, plant height, stem diameter, quantum efficiency of photosystem II (Fv/Fm), and soluble sugar of cassava decreased for both SC8 and SC124. The two varieties\' rhizosphere bacterial communities\' overall taxonomic structure was highly similar, but there were slight differences in relative abundance. SC124 mainly relied on Gamma-proteobacteria and Acidobacteriae in response to drought stress, and the abundance of this class was positively correlated with soil acid phosphatase. SC8 mainly relied on Actinobacteria in response to drought stress, and the abundance of this class was positively correlated with soil urease and soil saccharase. Overall, this study confirmed the key role of drought-induced rhizosphere bacteria in improving the adaptation of cassava to drought stress and clarified that this process is significantly related to variety.

This study investigated the gelling properties, rheological behaviour, and microstructure of heat-induced, low-salt myofibrillar protein (MP) gels containing different levels (2%, 4%, 6%, and 8%, w/w) of cross-linked (CTS) or acetylated (ATS) tapioca starch. The results indicated that either CTS or ATS significantly enhanced the gel strength and water-holding capacity of low-salt MP gels (P < 0.05), an outcome verified by the rheological behaviour test results under different modes. Furthermore, iodine-staining images indicated that the MP-dominated continuous phase gradually transited to a starch-dominated phase with increasing CTS or ATS levels, and 4% was the critical point for this phase transition. In addition, hydrophobic interactions and disulphide bonds constituted the major intermolecular forces of low-salt MP gels, effectively promoting phase transition. In brief, modified tapioca starches possess considerable potential application value in low-salt meat products.

A20/AN1 zinc-finger domain-containing genes are very promising candidates in improving plant tolerance to abiotic stresses, but considerably less is known about functions and mechanisms for many of them. In this study, Metip3 (5, and 7), cassava (Manihot esculenta) A20/AN1 genes carrying one A20 domain and one AN1 domain, were functionally characterized at different layers. Metip3 (5, and 7) proteins were all located in the nucleus. No interactions were found between these three proteins. Metip3 (5, and 7)-expressing Arabidopsis was more tolerant to multiple abiotic stresses by Na, Cd, Mn, Al, drought, high temperature, and low temperature. Metip3- and Metip5-expressing Arabidopsis was sensitive to Cu stress, while Metip7-expressing Arabidopsis was insensitive. The H2O2 production significantly decreased in all transgenic Arabidopsis, however, O2·- production significantly decreased in Metip3- and Metip5-expressing Arabidopsis but did not significantly changed in Metip7-expressing Arabidopsis under drought. Metip3 (5, and 7) expression-silenced cassava showed the decreased tolerance to drought and NaCl, presented significant decreases in superoxide dismutase and catalase activities and proline content, and displayed a significant increase in malondialdehyde content under drought. Taken together with transcriptome sequencing analysis, it is suggested that Metip5 gene can not only affect signal transduction related to plant hormone, mitogen activated protein kinases, and starch and sucrose metabolism, DRE-binding transcription factors, and antioxidants, conferring the drought tolerance, but also might deliver the signals from DREB2A INTERACTING PROTEIN1, E3 ubiquitin-protein ligases to proteasome, leading to the drought intolerance. The results are informative not only for further study on evolution of A20/AN1 genes but also for development of climate resilient crops.

CONCLUSIONS: MePMTR1 is involved in plant development and production as well as photosynthesis in plant. Melatonin is widely involved in plant growth and development as well as stress responses. Compared with the extending studies of melatonin in stress responses, the direct link between melatonin and plant development in the whole stages remains unclear. With the identification of phytomelatonin receptor PMTR1 in plants, melatonin signalling is becoming much clearer. However, the function of MePMTR1 in tropical crop cassava remains elusive. In this study, we found that overexpression of MePMTR1 showed larger biomass than wild type (WT), including higher number and area of leaves, weight, and accompanying with higher photosynthetic efficiency. Consistently, exogenous melatonin accelerated photosynthetic rate in Arabidopsis. In addition, MePMTR1-overexpressed plants exhibited more resistance to dark-induced senescence compared with WT, demonstrated by higher chlorophyll, lower hydrogen peroxide and superoxide content. In summary, this study illustrated that melatonin and its receptor regulate growth, development and senescence in plants, highlighting the potential application of melatonin and its receptor in improving crop yield and photosynthesis.

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.

Cassava, a pivotal tropical crop, exhibits rapid growth and possesses a substantial biomass. Its stem is rich in cellulose and serves as a crucial carbohydrate storage organ. The height and strength of stems restrict the mechanised operation and propagation of cassava. In this study, the triple helix transcription factor MeGT2.6 was identified through yeast one-hybrid assay using MeCesA1pro as bait, which is critical for cellulose synthesis. Over-expression and loss-of-function lines were generated, and results revealed that MeGT2.6 could promote a significant increase in the plant height, stem diameter, cell size and thickness of SCW of cassava plant. Specifically, MeGT2.6 upregulated the transcription activity of MeGA20ox1 and downregulated the expression level of MeGA2ox1, thereby enhancing the content of active GA3, resulting in a large cell size, high plant height and long stem diameter in cassava. Moreover, MeGT2.6 upregulated the transcription activity of MeCesA1, which promoted the synthesis of cellulose and hemicellulose and produced a thick secondary cell wall. Finally, MeGT2.6 could help supply additional substrates for the synthesis of cellulose and hemicellulose by upregulating the invertase genes (MeNINV1/6). Thus, MeGT2.6 was found to be a multiple regulator; it was involved in GA metabolism and sucrose decomposition and the synthesis of cellulose and hemicellulose.

MeFtsZ2-1 is a key gene for plant plastid division, but the mechanism by which MeFtsZ2-1 affects pigment accumulation in cassava (Manihot esculenta Crantz) through plastids remains unclear. We found that MeFtsZ2-1 overexpression in cassava (OE) exhibited darker colors of leaves, with increased levels of anthocyanins and carotenoids. Further observation via Transmission Electron Microscopy (TEM) revealed no apparent defects in chloroplast structure but an increase in the number of plastoglobule in OE leaves. RNA-seq results showed 1582 differentially expressed genes (DEGs) in leaves of OE. KEGG pathway analysis indicated that these DEGs were enriched in pathways related to flavonoid, anthocyanin, and carotenoid biosynthesis. This study reveals the role of MeFtsZ2-1 in cassava pigment accumulation from a physiological and transcriptomic perspective, providing a theoretical basis for improving cassava quality.

The vibrating superfine mill (VSM) is a machine that belongs to the micronization technique. In this study, VSM was employed to produce micronized tapioca starch by varying micronization times (15, 30, 45, and 60 min). The structural and physicochemical properties of the micronized starch were then examined. Scanning electron microscopy studies revealed that micronized starch was partially gelatinized, and the granule size dramatically increased when micronization time increased. X-ray diffraction patterns showed that the relative crystallinity was decreased from 24.67% (native) to 4.13% after micronization treatment for 15 min and slightly decreased after that. The solubility of micronized starch significantly increased as the micronization time increased, which was associated with the destruction of the starch crystalline structure. Differential scanning calorimetry investigations confirmed that micronized starch was \"partly gelatinized,\" and the degree of gelatinization increased to 81.27% when the micronization time was 60 min. The weight-average molar mass was reduced by 15.0% (15 min), 30.9% (30 min), 55.7% (45 min), and 70.5% (60 min), respectively, indicating that the molecular structure was seriously degraded. The results demonstrated that the physicochemical changes of micronized starch granules were related to the destruction of the starch structure. These observations would provide details on micronized starch and its potential applications. PRACTICAL APPLICATION: These observations would provide details on micronized starch and its potential applications. Moreover, we believe that when the structures of starches were known, it is probable that the effect of VSM on the structural and physicochemical properties change of other starches might be predicted by adjusting the processing time.