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Key messagePiriformospora indica symbiosis promoted the growth and photosynthesis, and simultaneously enhanced the resistance against insect herbivory by regulating sporamin-dependent defense in sweet potato.Piriformospora indica (P. indica), a versatile endophytic fungus, promotes the growth and confers resistance against multiple stresses by root colonization in plant hosts. In this study, the effects of P. indica colonization on the growth, physiological change, and herbivore resistance of leaf-vegetable sweet potato cultivar were investigated. P. indica symbiosis significantly improved the biomass in both above- and under-ground parts of sweet potato plants. In comparison with the non-colonized plants, the content of photosynthetic pigments and the efficiency of photosynthesis were increased in P. indica-colonized sweet potato plants. Further investigation showed that the activity of catalase was enhanced in both leaves and roots of sweet potato plants after colonization, but ascorbate peroxidase, peroxidase, and superoxide dismutase were not enhanced. Furthermore, the interaction between P. indica and sweet potato plants also showed the biological function in jasmonic acid (JA)-mediated defense. The plants colonized by P. indica had greatly increased JA accumulation and defense gene expressions, including IbNAC1, IbbHLH3, IbpreproHypSys, and sporamin, leading to elevated trypsin inhibitory activity, which was consistent with a reduced Spodoptera litura performance when larvae fed on the leaves of P. indica-colonized sweet potato plants. The root symbiosis of P. indica is helpful for the plant promoting growth and development and has a strong function as resistance inducers against herbivore attack in sweet potato cultivation by regulating sporamin-dependent defense.

Background The number of fibrous roots that develop into storage roots determines sweetpotato yield. The aim of the present study was to identify the molecular mechanisms involved in the initiation of storage root formation, by performing a detailed transcriptomic analysis of initiating storage roots using next-generation sequencing platforms. A two-step approach was undertaken: (1) generating a database for the sweetpotato root transcriptome using 454-Roche sequencing of a cDNA library created from pooled samples of two root types: fibrous and initiating storage roots; (2) comparing the expression profiles of initiating storage roots and fibrous roots, using the Illumina Genome Analyzer to sequence cDNA libraries of the two root types and map the data onto the root transcriptome database. Results Use of the 454-Roche platform generated a total of 524,607 reads, 85.6% of which were clustered into 55,296 contigs that matched 40,278 known genes. The reads, generated by the Illumina Genome Analyzer, were found to map to 31,284 contigs out of the 55,296 contigs serving as the database. A total of 8,353 contigs were found to exhibit differential expression between the two root types (at least 2.5-fold change). The Illumina-based differential expression results were validated for nine putative genes using quantitative real-time PCR. The differential expression profiles indicated down-regulation of classical root functions, such as transport, as well as down-regulation of lignin biosynthesis in initiating storage roots, and up-regulation of carbohydrate metabolism and starch biosynthesis. In addition, data indicated delicate control of regulators of meristematic tissue identity and maintenance, associated with the initiation of storage root formation. Conclusions This study adds a valuable resource of sweetpotato root transcript sequences to available data, facilitating the identification of genes of interest. This resource enabled us to identify genes that are involved in the earliest stage of storage root formation, highlighting the reduction in carbon flow toward phenylpropanoid biosynthesis and its delivery into carbohydrate metabolism and starch biosynthesis, as major events involved in storage root initiation. The novel transcripts related to storage root initiation identified in this study provide a starting point for further investigation into the molecular mechanisms underlying this process.

This study evaluated the responses of sweet potatoes to Cadmium (Cd) stress through pot experiments to theoretically substantiate their comprehensive applications in Cd-polluted agricultural land. The experiments included a CK treatment and three Cd stress treatments with 3, 30, and 150 mg/kg concentrations, respectively. We analyzed specified indicators of sweet potato at different growth periods, such as the individual plant growth, photosynthesis, antioxidant capacity, and carbohydrate Cd accumulation distribution. On this basis, the characteristics of the plant carbon metabolism in response to Cd stress throughout the growth cycle were explored. The results showed that T2 and T3 treatments inhibited the vine growth, leaf area expansion, stem diameter elongation, and tuberous root growth of sweet potato; notably, T3 treatment significantly increased the number of sweet potato branches. Under Cd stress, the synthesis of chlorophyll in sweet potato was significantly suppressed, and the Rubisco activity experienced significant reductions. With the increasing Cd concentration, the function of PS II was also affected. The soluble sugar content underwent no significant change in low Cd concentration treatments. In contrast, it decreased significantly under high Cd concentrations. Additionally, the tuberous root starch content decreased significantly with the increase in Cd concentration. Throughout the plant growth, the activity levels of catalase, peroxidase, and superoxide dismutase increased significantly in T2 and T3 treatments. By comparison, the superoxide dismutase activity in T1 treatment was significantly lower than that of CK. With the increasing application of Cd, its accumulation accordingly increased in various sweet potato organs. The the highest bioconcentration factor was detected in absorbing roots, while the tuberous roots had a lower bioconcentration factor and Cd accumulation. Moreover, the transfer factor from stem to petiole was the highest of the potato organs. These results demonstrated that sweet potatoes had a high Cd tolerance and a restoration potential for Cd-contaminated farmland.

N-(2-chloro-4-pyridyl)-N’-phenylurea (Forchlorfenuron, CPPU) is widely used in crop production to promote fruit growth. However, the mechanism of action in root and tuber crops remains unclear. Sweet potatoes are the third most important root crop, and the application of exogenous CPPU in the field production of sweet potatoes is of great significance. In this study, we characterised the effects of different concentrations of CPPU applied 30 days after planting on the agronomic traits of sweet potatoes, as well as the effects of applying 9 mg/L CPPU on endogenous hormones and gene expression in the stem tips and young roots of sweet potatoes. The results showed that spraying 9 mg/L CPPU on sweet potato cuttings 30 d after planting increased the total yield of sweet potato tubers, marketable tuber yield, tuber dry matter content, and soluble sugar content. Furthermore, the foliar application of 9 mg/L CPPU reduced the levels of GAs, auxins, and ABA in stem tips and young roots, while increasing CKs and SA content in stem tips and decreasing SA content in young roots. Transcriptome data analysis revealed that CPPU mainly regulates the growth and development of sweet potato tubers by promoting lignin synthesis, affecting the phenylpropanoid biosynthetic pathway, and regulating key genes in the carotenoid biosynthetic pathway. RT-qPCR results indicated that exogenous CPPU treatment induced an upregulation in the expression levels of most key genes and transcription factors. This study offers a new reference for enhancing the practical production of sweet potatoes, sheds new light on the impact of CPPU on the growth and development of root crops, and provides fresh insights into future research on sweet potato root tuber enlargement.

Global warming causes plant stress and reduces crop productivity. Cultivation of the warmer region crop sweet potato ( Ipomoea batatas (L.) Lam) in Northern regions can be an opportunity to benefit from climate warming, but there is little information of how growing season length interacts with agricultural practices such as nitrogen (N) fertilization. We studied the photosynthetic characteristics, biomass accumulation, carbon (C) and N contents of plant organs of the cultivar ‘Purple Bud’ in relation to the planting date (the 2nd of May, 10th of May, 20th of May, 30th of May and 10th of June) and N fertilization (kg ha -1 ; N0, N50, N100 and N150). Nitrogen content of leaves ( N L ) and tubers ( N T ) increased with N application dose and was moderately affected by planting time. Despite the fertilization-dependent increase of leaf N content, photosynthesis rate ( A ) was unaffected or somewhat reduced by N fertilization. This reflected reductions in stomatal conductance ( g s ) and ratio of intercellular CO 2 to ambient CO 2 ( C i / C a ), suggesting that enhanced N availability and concomitant increase in whole plant area resulted in reduced plant water availability. The highest values of leaf C/N ratio, tuber to root mass ratio and dry weight content of roots ( DW R ) were found in N0 plants and the ones planted on the 10th of May and 20th of May. Our results collectively demonstrate that the growth and productivity of sweet potato is strongly dependent on the length of the growing season, and can be further constrained by utilization efficiency of N. We conclude that future research should focus on optimum sweet potato cultivation technologies at Northern latitudes.

Background Anthocyanins, which have important biological functions and have a beneficial effect on human health, notably account for pigmentation in purple-fleshed sweet potato tuberous roots. Individual regulatory factors of anthocyanin biosynthesis have been identified; however, the regulatory network of anthocyanin biosynthesis in purple-fleshed sweet potato is unclear. Results We functionally determined that IbMYB340 cotransformed with IbbHLH2 in tobacco and strawberry receptacles induced anthocyanin accumulation, and the addition of IbNAC56a or IbNAC56b caused increased pigmentation. Furthermore, we confirmed the interaction of IbMYB340 with IbbHLH2 and IbNAC56a or IbNAC56b via yeast two-hybrid and firefly luciferase complementation assays; these proteins could form a MYB340-bHLH2-NAC56a or MYB340-bHLH2-NAC56b transcriptional complex to regulate anthocyanin biosynthesis by binding to the IbANS promoter rather than the IbUFGT promoter. Furthermore, it was found by a transient expression system in tobacco leaves that IbMYB44 could decrease anthocyanin accumulation. Moreover, the interaction of IbMYB44 with IbMYB340 and IbNAC56a or IbNAC56b was verified. This result suggested that IbMYB44 acts as a repressor of anthocyanin in sweet potato. Conclusions The repressor IbMYB44 affected anthocyanin biosynthesis by competitively inhibiting the IbMYB340 - IbbHLH2 - IbNAC56a or IbMYB340 - IbbHLH2 - IbNAC56b regulatory complex formation. Overall, the present study proposed a novel regulatory network whereby several vital TFs play key roles in regulating anthocyanin biosynthesis, and it provides strong insight into the potential mechanism underlying anthocyanin biosynthesis in sweet potato tuberous roots with purple color.

Single-cell transcriptome sequencing (scRNA-seq) is a powerful tool for describing the transcriptome dynamics of plant development but has not yet been utilized to analyze the tissue ontology of sweetpotato. This study established a stable method for isolating single protoplast cells for scRNA-seq to reveal the cell heterogeneity of sweetpotato root tip meristems at the single-cell level. The study analyzed 12,172 single cells and 27,355 genes in the root tips of the sweetpotato variety Guangshu 87, which were distributed into 15 cell clusters. Pseudo-time analysis showed that there were transitional cells in the apical development trajectory of mature cell types from stem cell niches. Furthermore, we identified novel development regulators of sweetpotato tubers via trajectory analysis. The transcription factor IbGATA4 was highly expressed in the adventitious roots during the development of sweetpotato root tips, where it may regulate the development of sweetpotato root tips. In addition, significant differences were observed in the transcriptional profiles of cell types between sweetpotato, Arabidopsis thaliana , and maize. This study mapped the single-cell transcriptome of sweetpotato root tips, laying a foundation for studying the types, functions, differentiation, and development of sweetpotato root tip cells. Highlights This is the first single-cell transcriptional atlas of sweetpotato root apex tissue. Single-cell analysis of stem cell niche initiation showed unique transitional states. Sweetpotato, Arabidopsis , and maize root tip cell types were correlated. GATA4 may be involved in regulating sweetpotato root tip development.

MicroRNAs (miRNAs) are small noncoding RNAs which post-transcriptionally regulate gene expression by directing mRNA cleavage or translational inhibition. miRNAs play multiple roles in the growth, development and stress responses in plants. However, little is known of the wounding-responsive miRNAs and their regulation. Here, we investigated the expression patterns of microR828 (miR828) on wounding in sweet potato (Ipomoea batatas cv Tainung 57). The expression of miR828 was only detected in leaves, and was induced by wounding rather than by ethylene, hydrogen peroxide (H2O2), methyl jasmonate or nitric oxide (NO). Moreover, cyclic guanosine monophosphate (cGMP) was necessary for miR828 accumulation in leaves on wounding. Two miR828 target candidates, named IbMYB and IbTLD, were obtained by cDNA cloning, and their mRNA cleavage caused by miR828 was confirmed by cleavage site mapping, agro-infiltration and transgenics studies. The reduction in IbMYB and IbTLD expression coincided with the induction of miR828, demonstrating thatIbMYB and IbTLD might be miR828 targets. Furthermore, transgenic sweet potato overexpressing miR828 precursor affected lignin and H2O2 contents. These results showed that cGMP could regulate wounding-responsive miR828, which repressed the expression of IbMYB and IbTLD. Subsequently, lignin and H2O2 were accumulated to participate in defense mechanisms.

Myo‐inositol‐1‐phosphate synthase (MIPS) is a key rate limiting enzyme in myo‐inositol biosynthesis. The MIPS gene has been shown to improve tolerance to abiotic stresses in several plant species. However, its role in resistance to biotic stresses has not been reported. In this study, we found that expression of the sweet potato IbMIPS1 gene was induced by NaCl, polyethylene glycol (PEG), abscisic acid (ABA) and stem nematodes. Its overexpression significantly enhanced stem nematode resistance as well as salt and drought tolerance in transgenic sweet potato under field conditions. Transcriptome and real‐time quantitative PCR analyses showed that overexpression of IbMIPS1 up‐regulated the genes involved in inositol biosynthesis, phosphatidylinositol (PI) and ABA signalling pathways, stress responses, photosynthesis and ROS‐scavenging system under salt, drought and stem nematode stresses. Inositol, inositol‐1,4,5‐trisphosphate (IP₃), phosphatidic acid (PA), Ca²⁺, ABA, K⁺, proline and trehalose content was significantly increased, whereas malonaldehyde (MDA), Na⁺ and H₂O₂ content was significantly decreased in the transgenic plants under salt and drought stresses. After stem nematode infection, the significant increase of inositol, IP₃, PA, Ca²⁺, ABA, callose and lignin content and significant reduction of MDA content were found, and a rapid increase of H₂O₂ levels was observed, peaked at 1 to 2 days and thereafter declined in the transgenic plants. This study indicates that the IbMIPS1 gene has the potential to be used to improve the resistance to biotic and abiotic stresses in plants.

Sweet potato (Ipomoea batatas L. [Lam.]) ranks among the top six most important food crops in the world. It is widely grown throughout the world with high and stable yield, strong adaptability, rich nutrient content, and multiple uses. However, little is known about the molecular biology of this important non-model organism due to lack of genomic resources. Hence, studies based on high-throughput sequencing technologies are needed to get a comprehensive and integrated genomic resource and better understanding of gene expression patterns in different tissues and at various developmental stages. Illumina paired-end (PE) RNA-Sequencing was performed, and generated 48.7 million of 75 bp PE reads. These reads were de novo assembled into 128,052 transcripts (≥ 100 bp), which correspond to 41.1 million base pairs, by using a combined assembly strategy. Transcripts were annotated by Blast2GO and 51,763 transcripts got BLASTX hits, in which 39,677 transcripts have GO terms and 14,117 have ECs that are associated with 147 KEGG pathways. Furthermore, transcriptome differences of seven tissues were analyzed by using Illumina digital gene expression (DGE) tag profiling and numerous differentially and specifically expressed transcripts were identified. Moreover, the expression characteristics of genes involved in viral genomes, starch metabolism and potential stress tolerance and insect resistance were also identified. The combined de novo transcriptome assembly strategy can be applied to other organisms whose reference genomes are not available. The data provided here represent the most comprehensive and integrated genomic resources for cloning and identifying genes of interest in sweet potato. Characterization of sweet potato transcriptome provides an effective tool for better understanding the molecular mechanisms of cellular processes including development of leaves and storage roots, tissue-specific gene expression, potential biotic and abiotic stress response in sweet potato.