Exploration of Raw Pigmented-Fleshed Sweet Potatoes Volatile Organic Compounds and the Precursors.

Sweet potato provides rich nutrients and bioactive substances for the human diet. In this study, the volatile organic compounds of five pigmented-fleshed sweet potato cultivars were determined, the characteristic aroma compounds were screened, and a correlation analysis was carried out with the aroma precursors. In total, 66 volatile organic compounds were identified. Terpenoids and aldehydes were the main volatile compounds, accounting for 59% and 17%, respectively. Fifteen compounds, including seven aldehydes, six terpenes, one furan, and phenol, were identified as key aromatic compounds for sweet potato using relative odor activity values (ROAVs) and contributed to flower, sweet, and fat flavors. The OR sample exhibited a significant presence of trans-ß-Ionone, while the Y sample showed high levels of benzaldehyde. Starch, soluble sugars, 20 amino acids, and 25 fatty acids were detected as volatile compounds precursors. Among them, total starch (57.2%), phenylalanine (126.82 ± 0.02 g/g), and fatty acids (6.45 µg/mg) were all most abundant in Y, and LY contained the most soluble sugar (14.65%). The results of the correlation analysis revealed the significant correlations were identified between seven carotenoids and trans-ß-Ionone, soluble sugar and nerol, two fatty acids and hexanal, phenylalanine and 10 fatty acids with benzaldehyde, respectively. In general, terpenoids and aldehydes were identified as the main key aromatic compounds in sweet potatoes, and carotenoids had more influence on the aroma of OR than other cultivars. Soluble sugars, amino acids, and fatty acids probably serve as important precursors for some key aroma compounds in sweet potatoes. These findings provide valuable insights for the formation of sweet potato aroma.

Genetic fingerprint construction and genetic diversity analysis of sweet potato (Ipomoea batatas) germplasm resources.

BACKGROUND: China is the largest producer of sweet potato in the world, accounting for 57.0% of the global output. Germplasm resources are the basis for promoting innovations in the seed industry and ensuring food security. Individual and accurate identification of sweet potato germplasm is an important part of conservation and efficient utilization. RESULTS: In this study, nine pairs of simple sequence repeat molecular markers and 16 morphological markers were used to construct genetic fingerprints for sweet potato individual identification. Combined with basic information, typical phenotypic photographs, genotype peak graphs, and a two-dimensional code for detection and identification were generated. Finally, a genetic fingerprint database containing 1021 sweet potato germplasm resources in the "National Germplasm Guangzhou Sweet Potato Nursery Genebank in China" was constructed. Genetic diversity analysis of the 1021 sweet potato genotypes using the nine pairs of simple sequence repeat markers revealed a narrow genetic variation range of Chinese native sweet potato germplasm resources, and Chinese germplasm was close to that from Japan and the United States, far from that from the Philippines and Thailand, and the furthest from that from Peru. Sweet potato germplasm resources from Peru had the richest genetic diversity, supporting the view that Peru is the center of origin and domestication of sweet potato varieties. CONCLUSIONS: Overall, this study provides scientific guidance for the conservation, identification, and utilization of sweet potato germplasm resources and offers a reference to facilitate the discovery of important genes to boost sweet potato breeding.

Combining Metabolomics and Transcriptomics to Reveal the Mechanism of Coloration in Purple and Cream Mutant of Sweet Potato (Ipomoea batatas L.).

Purple sweet potato is considered as a healthy food because of its high anthocyanins. To understand the coloring mechanism and quality change between purple-fleshed sweet potato (cv. Xuzi201) and its cream fleshed mutant (M1001), a combined metabolomic and transcriptomic analysis was performed. The metabolome data showed that 4 anthocyanins, 19 flavones, 6 flavanones, and 4 flavonols dramatically decreased in M1001, while the contents of 3 isoflavones, 3 flavonols, 4 catechins, and 2 proanthocyanins increased. Transcriptomic analyses indicated that the expression of 49 structural genes in the flavonoid pathway and transcription factors (TFs) (e.g., bHLH2, R2R3-MYB, MYB1) inducting anthocyanin biosynthesis were downregulated, but the repressor MYB44 was upregulated. The IbMYB1-2 gene was detected as a mutation gene in M1001, which is responsible for anthocyanin accumulation in the storage roots. Thus, the deficiency of purple color in the mutant is due to the lack of anthocyanin accumulation which was regulated by IbMYB1. Moreover, the accumulation of starch and aromatic volatiles was significantly different between Xuzi201 and M1001. These results not only revealed the mechanism of color mutation but also uncovered certain health-promoting compounds in sweet potato.

Exploration of molecular mechanism of intraspecific cross-incompatibility in sweetpotato by transcriptome and metabolome analysis.

Cross-incompatibility, frequently happening in intraspecific varieties, has seriously restricted sweetpotato breeding. However, the mechanism of sweetpotato intraspecific cross-incompatibility (ICI) remains largely unexplored, especially for molecular mechanism. Treatment by inducible reagent developed by our lab provides a method to generate material for mechanism study, which could promote incompatible pollen germination and tube growth in the ICI group. Based on the differential phenotypes between treated and untreated samples, transcriptome and metabolome were employed to explore the molecular mechanism of sweetpotato ICI in this study, taking varieties 'Guangshu 146' and 'Shangshu 19', a typical incompatible combination, as materials. The results from transcriptome analysis showed oxidation-reduction, cell wall metabolism, plant-pathogen interaction, and plant hormone signal transduction were the essential pathways for sweetpotato ICI regulation. The differentially expressed genes (DEGs) enriched in these pathways were the important candidate genes to response ICI. Metabolome analysis showed that multiple differential metabolites (DMs) involved oxidation-reduction were identified. The most significant DM identified in comparison between compatible and incompatible samples was vitexin-2-O-glucoside, a flavonoid metabolite. Corresponding to it, cytochrome P450s were the most DEGs identified in oxidation-reduction, which were implicated in flavonoid biosynthesis. It further suggested oxidation-reduction play an important role in sweetpotato ICI regulation. To validate function of oxidation-reduction, reactive oxygen species (ROS) was detected in compatible and incompatible samples. The green fluorescence was observed in incompatible but not in compatible samples. It indicated ROS regulated by oxidation-reduction is important pathway to response sweetpotato ICI. The results in this study would provide valuable insights into molecular mechanisms for sweetpotato ICI.

Phosphate starvation responsive GmSPX5 mediates nodule growth through interaction with GmNF-YC4 in soybean (Glycine max).

Phosphorus (P) deficiency adversely affects nodule development as reflected by reduced nodule fresh weight in legume plants. Though mechanisms underlying nodule adaptation to P deficiency have been studied extensively, it remains largely unknown which regulator mediates nodule adaptation to P deficiency. In this study, GUS staining and quantitative reverse transcription-PCR analysis reveal that the SPX member GmSPX5 is preferentially expressed in soybean (Glycine max) nodules. Overexpression of GmSPX5 enhanced soybean nodule development particularly under phosphate (Pi) sufficient conditions. However, the Pi concentration was not affected in soybean tissues (i.e., leaves, roots, and nodules) of GmSPX5 overexpression or suppression lines, which distinguished it from other well-known SPX members functioning in control of Pi homeostasis in plants. Furthermore, GmSPX5 was observed to interact with the transcription factor GmNF-YC4 in vivo and in vitro. Overexpression of either GmSPX5 or GmNF-YC4 significantly upregulated the expression levels of five asparagine synthetase-related genes (i.e., GmASL2-6) in soybean nodules. Meanwhile, yeast one-hybrid and luciferase activity assays strongly suggested that interactions of GmSPX5 and GmNF-YC4 activate GmASL6 expression through enhancing GmNF-YC4 binding of the GmASL6 promoter. These results not only demonstrate the GmSPX5-GmNF-YC4-GmASL6 regulatory pathway mediating soybean nodule development, but also considerably improve our understanding of SPX functions in legume crops.

Isolation and Identification of Trichoderma asperellum, the Novel Causal Agent of Green Mold Disease in Sweetpotato.

Postharvest disease is an important limiting factor for sweetpotato production. Recently, a new green mold disease was found in sweetpotato storage roots. To investigate the mechanism underlying the pathogenesis of the disease, the pathogen was isolated and identified based on morphological and molecular features, and its characteristics were further analyzed by pathogenic and antagonistic evaluations. The results showed that the isolated pathogen (CRI-Ta1) was identified as Trichoderma asperellum based on the similar growth and morphological features with Trichoderma spp., 99% homology of internal transcribed spacer (ITS) sequence, and membership to the same phylogenetic group with the model strain of T. asperellum (CBS 433.97). The pathogenic analysis revealed that CRI-Ta1 could cause green mold disease through wound infection on the storage roots and the strains reisolated from infected storage roots could cause disease in different sweetpotato varieties, which was fulfilled in Koch's postulate. Moreover, CRI-Ta1 could also infect other common crop species, including chestnut, carrot, apple, pear, and others. It indicated that CRI-Ta1 was the pathogen to the storage roots of sweetpotato and had a wide host range. Additionally, in vitro antagonistic evaluation showed that CRI-Ta1 effectively inhibited the growth of common sweetpotato pathogens, including Fusarium solani and Rhizopus nigricans. However, further research is needed on the potential of CRI-Ta1 to control sweetpotato diseases in vivo. Collectively, our findings provided valuable insights into the characteristics of the T. asperellum CRI-Ta1 in sweetpotato and would be helpful to the prevention and control of sweetpotato green mold disease.

Effect of domestic cooking methods on the anthocyanins and antioxidant activity of deeply purple-fleshed sweetpotato GZ9.

Purple-fleshed sweetpotatoes (PFSPs) are considered to be a healthy food and there are many methods to process in family. This study aimed to investigate the effects of various domestic cooking on the anthocyanin variation and antioxidant activity of a newly bred purple-fleshed cultivar Guangzishu 9 (GZ9) with anthocyanin content up to 1,500 mg/100g dry weight. As a result, total 15 individual anthocyanins were separated and identified by using UPLC-QTOF-MS. Top three anthocyanins were cyanidin 3-dicaffeoyl sophoroside-5-glucoside, cyanidin 3-caffeoyl- p-coumaryl sophoroside-5-glucoside and peonidin 3-caffeoyl-p-hydroxybenzoyl sophoroside-5-glucoside, which accounting for 57.27% of the total anthocyanin content. Acylated anthocyanins were the major constituents in GZ9, and the type of anthocyanins was dominated by cyanidin. Boiling, steaming and mircrowaving had no significant effect on the total anthocyanin content. But baking, frying, air-frying and stir-frying reduced 11-45% of total anthocyanin content. Through ABTS+ radical scavenging capacity and reducing power, antioxidant variations were also observed during different family cooking, and the variation had a strong correlation with total anthocyanin content.

Temporal patterns of gene expression associated with tuberous root formation and development in sweetpotato (Ipomoea batatas).

BACKGROUND: The tuberous root of sweetpotato is undisputedly an important organ from agronomic and biological perspectives. Little is known regarding the regulatory networks programming tuberous root formation and development. RESULTS: Here, as a first step toward understanding these networks, we analyzed and characterized the genome-wide transcriptional profiling and dynamics of sweetpotato root in seven distinct developmental stages using a customized microarray containing 39,724 genes. Analysis of these genes identified temporal programs of gene expression, including hundreds of transcription factor (TF) genes. We found that most genes active in roots were shared across all developmental stages, although significant quantitative changes in gene abundance were observed for 5,368 (including 435 TFs) genes. Clustering analysis of these differentially expressed genes pointed out six distinct expression patterns during root development. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that genes involved in different processes were enriched at specific stages of root development. In contrast with the large number of shared expressed genes in root development, each stage or period of root development has only a small number of specific genes. In total, 712 (including 27 TFs) and 1,840 (including 115 TFs) genes were identified as root-stage and root-period specific, respectively at the level of microarray. Several of the specific TF genes are known regulators of root development, including DA1-related protein, SHORT-ROOT and BEL1-like. The remaining TFs with unknown roles would also play critical regulatory roles during sweetpotato tuberous root formation and development. CONCLUSIONS: The results generated in this study provided spatiotemporal patterns of root gene expression in support of future efforts for understanding the underlying molecular mechanism that control sweetpotato yield and quality.

Comparative characterization of GmSPX members reveals that GmSPX3 is involved in phosphate homeostasis in soybean.

BACKGROUND AND AIMS: Proteins containing the SPX (SYG1/Pho81/XPR1) domain are vital components in the phosphorus (P) signalling pathway, and regulate phosphate (Pi) homeostasis in plants. However, the characteristics and functions of GmSPX members in soybean (Glycine max) remain largely unknown. METHODS: BLAST searching revealed nine GmSPX members in the soybean genome. Subsequently, expression patterns of GmSPX members were investigated in various tissues of soybean grown in nutrient solution or sand culture through quantitative real-time PCR (qPCR) analysis. Sub-cellular localization of GmSPX was examined via transient expression of 35S:GmSPX-GFP in epidermal cells of onion (Allium cepa). Finally, soybean transgenic composite plants were generated to study GmSPX3 functions. KEY RESULTS: Nine GmSPX members were identified, which were classified into three groups based on phylogenetic analysis. Diverse responses of GmSPX members to deficiencies of nutrients (nitrogen, phosphorus, potassium and iron) or inoculation of arbuscular mycorrhizal fungi and rhizobia were observed in soybean. In addition, variations of sub-cellular localization of GmSPX members were found. Among them, GmSPX3, GmSPX7 and GmSPX8 were localized in the nuclei, and the other GmSPX members were confined to the nuclei and cytoplasm. The nuclear-localized and Pi starvation responsive-gene, GmSPX3, was functionally analysed in soybean transgenic composite plants. Overexpression of GmSPX3 led to increased P concentrations in both shoots and roots in the high-P treatment, and increased transcription of seven Pi starvation-responsive genes in soybean hairy roots. CONCLUSIONS: Taken together, the results suggest that GmSPX3 is a positive regulator in the P signalling network, and controls Pi homeostasis in soybean.

SPX1 is an important component in the phosphorus signalling network of common bean regulating root growth and phosphorus homeostasis.

Proteins containing the SPX domain are believed to play vital roles in the phosphorus (P) signalling network in plants. However, the functions of SPX proteins in legumes remain largely unknown. In this study, three SPX members, PvSPX1-PvSPX3 were cloned from common bean (Phaseolus vulgaris L.). It was found that the transcripts of all three PvSPX members were significantly enhanced in both bean leaves and roots by phosphate (Pi) starvation. Among them, the expression of nuclear localized PvSPX1 showed more sensitive and rapid responses to Pi starvation. Consistently, only overexpression of PvSPX1 resulted in increased root P concentration and modified morphology of transgenic bean hairy roots, such as inhibited root growth and an enlarged root hair zone. It was further demonstrated that PvSPX1 transcripts were up-regulated by overexpressing PvPHR1, and overexpressing PvSPX1 led to increased transcripts of 10 Pi starvation-responsive genes in transgenic bean hairy roots. Taken together, it is suggested that PvSPX1 is a positive regulator in the P signalling network of common bean, and is downstream of PvPHR1.

Low pH, aluminum, and phosphorus coordinately regulate malate exudation through GmALMT1 to improve soybean adaptation to acid soils.

Low pH, aluminum (Al) toxicity, and low phosphorus (P) often coexist and are heterogeneously distributed in acid soils. To date, the underlying mechanisms of crop adaptation to these multiple factors on acid soils remain poorly understood. In this study, we found that P addition to acid soils could stimulate Al tolerance, especially for the P-efficient genotype HN89. Subsequent hydroponic studies demonstrated that solution pH, Al, and P levels coordinately altered soybean (Glycine max) root growth and malate exudation. Interestingly, HN89 released more malate under conditions mimicking acid soils (low pH, +P, and +Al), suggesting that root malate exudation might be critical for soybean adaptation to both Al toxicity and P deficiency on acid soils. GmALMT1, a soybean malate transporter gene, was cloned from the Al-treated root tips of HN89. Like root malate exudation, GmALMT1 expression was also pH dependent, being suppressed by low pH but enhanced by Al plus P addition in roots of HN89. Quantitative real-time PCR, transient expression of a GmALMT1-yellow fluorescent protein chimera in Arabidopsis protoplasts, and electrophysiological analysis of Xenopus laevis oocytes expressing GmALMT1 demonstrated that GmALMT1 encodes a root cell plasma membrane transporter that mediates malate efflux in an extracellular pH-dependent and Al-independent manner. Overexpression of GmALMT1 in transgenic Arabidopsis, as well as overexpression and knockdown of GmALMT1 in transgenic soybean hairy roots, indicated that GmALMT1-mediated root malate efflux does underlie soybean Al tolerance. Taken together, our results suggest that malate exudation is an important component of soybean adaptation to acid soils and is coordinately regulated by three factors, pH, Al, and P, through the regulation of GmALMT1 expression and GmALMT1 function.

Comparative analysis of PvPAP gene family and their functions in response to phosphorus deficiency in common bean.

BACKGROUND: Purple acid phosphatases (PAPs) play a vital role in adaptive strategies of plants to phosphorus (P) deficiency. However, their functions in relation to P efficiency are fragmentary in common bean. PRINCIPAL FINDINGS: Five PvPAPs were isolated and sequenced in common bean. Phylogenetic analysis showed that PvPAPs could be classified into two groups, including a small group with low molecular mass, and a large group with high molecular mass. Among them, PvPAP3, PvPAP4 and PvPAP5 belong to the small group, while the other two belong to the large group. Transient expression of 35S:PvPAPs-GFP on onion epidermal cells verified the variations of subcellular localization among PvPAPs, suggesting functional diversities of PvPAPs in common bean. Quantitative PCR results showed that most PvPAPs were up-regulated by phosphate (Pi) starvation. Among them, the expression of the small group PvPAPs responded more to Pi starvation, especially in the roots of G19833, the P-efficient genotype. However, only overexpressing PvPAP1 and PvPAP3 could result in significantly increased utilization of extracellular dNTPs in the transgenic bean hairy roots. Furthermore, overexpressing PvPAP3 in Arabidopsis enhanced both plant growth and total P content when dNTPs were supplied as the sole external P source. CONCLUSIONS: The results suggest that PvPAPs in bean varied in protein structure, response to P deficiency and subcellular localization. Among them, both PvPAP1 and PvPAP3 might function as utilization of extracellular dNTPs.

Characterization of two putative protein phosphatase genes and their involvement in phosphorus efficiency in Phaseolus vulgaris.

Protein dephosphorylation mediated by protein phosphatases plays a major role in signal transduction of plant responses to environmental stresses. In this study, two putative protein phosphatases, PvPS2:1 and PvPS2:2 were identified and characterized in bean (Phaseolus vulgaris). The two PvPS2 members were found to be localized to the plasma membrane and the nucleus by transient expression of PvPS2:GFP in onion epidermal cells. Transcripts of the two PvPS2 genes were significantly increased by phosphate (P(i) ) starvation in the two bean genotypes, G19833 (a P-efficient genotype) and DOR364 (a P-inefficient genotype). However, G19833 exhibited higher PvPS2:1 expression levels than DOR364 in both leaves and roots during P(i) starvation. Increased transcription of PvPS2:1 in response to P(i) starvation was further verified through histochemical analysis of PvPS2:1 promoter fusion ß-glucuronidase (GUS) in transgenic Arabidopsis plants. Analysis of PvPS2:1 overexpression lines in bean hairy roots and Arabidopsis showed that PvS2:1 was involved in root growth and P accumulation. Furthermore, expression levels of two P(i) starvation responsive genes were upregulated and the APase activities were enhanced in the overexpressing PvPS2:1 Arabidopsis lines. Taken together, our results strongly suggested that PvPS2:1 positively regulated plant responses to P(i) starvation, and could be further targeted as a candidate gene to improve crop P efficiency.