Integrated mRNA and miRNA transcriptome analysis reveals a regulatory network for tuber expansion in Chinese yam (Dioscorea opposita)

Growth and physiological response of Yulu Hippophae rhamnoides to drought stress and its omics analysis

Hippophae rhamnoides (H. rhamnoides) is the primary tree species known for its ecological and economic benefits in arid and semi-arid regions. Understanding the response of H. rhamnoides roots to drought stress is essential for promoting the development of varieties. One-year-old Yulu H. rhamnoides was utilized as the experimental material, and three water gradients were established: control (CK), moderate (T1) and severe (T2), over a period of 120 days. The phenotypic traits and physiological indies were assessed and analyzed, while the roots were subjected by RNA-Seq transcriptome and Tandem Mass Tags (TMT) proteome analysis. Drought stress significantly reduced the plant height, ground diameter, root biomass and superoxide dismutase activity; however, the main root length increased. In comparison with CK, a total of 5789 and 5594 differential genes, as well as 63 and 1012 differential proteins, were identified in T1 and T2, respectively. The combined analysis of transcriptome and proteome showed that the number of differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) associated with T1, T2 and CK was 28 and 126, respectively, with 7 and 36 genes achieving effective KEGG annotation. In T1 and T2, the differential genes were significantly enriched in the plant hormone signal transduction pathway, but there was no significant enrichment in the protein expression profile. In T2, 38 plant hormone signal transduction function genes and 10 peroxisome related genes were identified. With the increase of drought stress, the combined expression of DEGs and DEPs increased. Yulu H. rhamnoides may allocate more resources toward CAT while simultaneously decreasing SOD and POD to mitigate the oxidative stress induced by drought. Furthermore, the molecular mechanisms underlying plant hormone signal transduction and peroxisome-related genes in the roots of H. rhamnoides were discussed in greater detail.

Comparative genome-wide characterization of salt responsive micro RNA and their targets through integrated small RNA and de novo transcriptome profiling in sugarcane and its wild relative Erianthus arundinaceus

Soil salinity and saline irrigation water are major constraints in sugarcane affecting the production of cane and sugar yield. To understand the salinity induced responses and to identify novel genomic resources, integrated de novo transcriptome and small RNA sequencing in sugarcane wild relative, Erianthus arundinaceus salt tolerant accession IND 99-907 and salt-sensitive sugarcane genotype Co 97010 were performed. A total of 362 known miRNAs belonging to 62 families and 353 miRNAs belonging to 63 families were abundant in IND 99-907 and Co 97010 respectively. The miRNA families such as miR156, miR160, miR166, miR167, miR169, miR171, miR395, miR399, miR437 and miR5568 were the most abundant with more than ten members in both genotypes. The differential expression analysis of miRNA reveals that 221 known miRNAs belonging to 48 families and 130 known miRNAs belonging to 42 families were differentially expressed in IND 99-907 and Co 97010 respectively. A total of 12,693 and 7982 miRNA targets against the monoploid mosaic genome and a total of 15,031 and 12,152 miRNA targets against the de novo transcriptome were identified for differentially expressed known miRNAs of IND 99-907 and Co 97010 respectively. The gene ontology (GO) enrichment analysis of the miRNA targets revealed that 24, 12 and 14 enriched GO terms (FDR < 0.05) for biological process, molecular function and cellular component respectively. These miRNAs have many targets that associated in regulation of biotic and abiotic stresses. Thus, the genomic resources generated through this study are useful for sugarcane crop improvement through biotechnological and advanced breeding approaches.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03867-7.

Selection of suitable reference genes for qPCR normalization in different developmental stages of Oenanthe javanica

Gene expression analysis is widely used to unravel molecular regulatory mechanisms and identify key genes in plants. Appropriate reference gene is an important prerequisite to ensure the accuracy and reliability of qPCR analysis results. Water dropwort is a plant of the Oenanthe genus in the Apiaceae family, which has high economic benefits. However, the underlying molecular regulatory mechanisms in the growth and development of water dropwort have not been fully understood and the appropriate reference genes in different developmental stages of water dropwort not yet reported. In this study, 10 candidate reference genes (ACTIN, PP2A, SAND, EF-1α, GAPDH, UBQ, MIP, TBP, RPS-18, eIF-4α) were identified and cloned from Oenanthe javanica. The qPCR primers of candidate reference genes were designed and verified. Four statistical algorithms, geNorm, NormFinder, BestKeeper and RefFinder were used to evaluate the expression stability of 10 candidate reference genes in different developmental stages of water dropwort. The results showed that TBP and UBQ were the most stable genes in different developmental stages of water dropwort, while GAPDH was the most unstable gene. The normalization of EXP1 genes at different developmental stages further confirmed the reliability of internal reference genes. The results of this study provide a theoretical basis for selecting appropriate internal reference genes in different developmental stages of water dropwort. This study also provides technical support and reliable basis for the expression analysis of key genes in different developmental stages of water dropwort.

Transcriptome profiling reveals the genes involved in tuberous root expansion in Pueraria (Pueraria montana var. thomsonii)

BACKGROUND

Pueraria is a dry root commonly used in Traditional Chinese Medicine or as food and fodder, and tuberous root expansion is an important agronomic characteristic that influences its yield. However, no specific genes regulating tuberous root expansion in Pueraria have been identified. Therefore, we aimed to explore the expansion mechanism of Pueraria at six developmental stages (P1-P6), by profiling the tuberous roots of an annual local variety "Gange No.1" harvested at 105, 135, 165, 195, 225, and 255 days after transplanting.

RESULTS

Observations of the tuberous root phenotype and cell microstructural morphology revealed that the P3 stage was a critical boundary point in the expansion process, which was preceded by a thickening diameter and yield gain rapidly of the tuberous roots, and followed by longitudinal elongation at both ends. A total of 17,441 differentially expressed genes (DEGs) were identified by comparing the P1 stage (unexpanded) against the P2-P6 stages (expanded) using transcriptome sequencing; 386 differential genes were shared across the six developmental stages. KEGG pathway enrichment analysis showed that the DEGs shared by P1 and P2-P6 stages were mainly involved in pathways related to the "cell wall and cell cycle", "plant hormone signal transduction", "sucrose and starch metabolism", and "transcription factor (TF)". The finding is consistent with the physiological data collected on changes in sugar, starch, and hormone contents. In addition, TFs including bHLHs, AP2s, ERFs, MYBs, WRKYs, and bZIPs were involved in cell differentiation, division, and expansion, which may relate to tuberous root expansion. The combination of KEGG and trend analyses revealed six essential candidate genes involved in tuberous root expansion; of them, CDC48, ARF, and EXP genes were significantly upregulated during tuberous root expansion while INV, EXT, and XTH genes were significantly downregulated.

CONCLUSION

Our findings provide new insights into the complex mechanisms of tuberous root expansion in Pueraria and candidate target genes, which can aid in increasing Pueraria yield.

Selection of Reliable Reference Genes for Gene Expression Normalization in Sagittaria trifolia

Real-time quantitative PCR (RT-qPCR) is a method with high sensitivity and convenience that has been extensively used to analyze the expression level of target genes. A reference gene with a highly stable expression is required to ensure the accuracy of experimental results. However, the report on appropriate reference genes in arrowheads (Sagittaria trifolia) is still limited. In this study, eight candidate reference genes (ACT5, UBQ, GAPDH, CYP, NAC, IDH, SLEEPER and PLA) were selected. The candidate genes were employed in a RT-qPCR assay in different tissues at different developmental stages of the same tissue (including corm, leaf and leafstalk) in arrowheads. Five statistical algorithms, GeNorm, NormFinder, BestKeeper, delta cycle threshold (ΔCt) and RefFinder, were used to evaluate the stability of these genes' expressions in order to identify the appropriate reference genes. The results showed that UBQ was the optimum reference gene in leaf, leafstalk, root, stolon and corm, IDH exhibited the most stable expression during the expansion of corm, UBQ and PLA were the most stable reference genes in developmental stages of leaf and leafstalk, respectively. Finally, the reliability of reference genes was further confirmed by the normalization of PDS and EXP1 genes under different arrowhead tissues and developmental stages of corm, respectively. This study constitutes important guidance for the selection of reliable reference genes for analyzing the tissue- and developmental-stage-specific expression of genes in arrowheads.

Transcriptomic analysis of Chinese yam (Dioscorea polystachya Turcz.) variants indicates brassinosteroid involvement in tuber development

Dioscorea is an important but underutilized genus of flowering plants that grows predominantly in tropical and subtropical regions. Several species, known as yam, develop large underground tubers and aerial bulbils that are used as food. The Chinese yam (D. polystachya Turcz.) is one of the few Dioscorea species that grows well in temperate regions and has been proposed as a climate-resilient crop to enhance food security in Europe. However, the fragile, club-like tubers are unsuitable for mechanical harvesting, which is facilitated by shorter and thicker storage organs. Brassinosteroids (BRs) play a key role in plant cell division, cell elongation and proliferation, as well as in the gravitropic response. We collected RNA-Seq data from the head, middle and tip of two tuber shape variants: F60 (long, thin) and F2000 (short, thick). Comparative transcriptome analysis of F60 vs. F2000 revealed 30,229 differentially expressed genes (DEGs), 1,393 of which were differentially expressed in the growing tip. Several DEGs are involved in steroid/BR biosynthesis or signaling, or may be regulated by BRs. The quantification of endogenous BRs revealed higher levels of castasterone (CS), 28-norCS, 28-homoCS and brassinolide in F2000 compared to F60 tubers. The highest BR levels were detected in the growing tip, and CS was the most abundant (439.6 ± 196.41 pmol/g in F2000 and 365.6 ± 112.78 pmol/g in F60). Exogenous 24-epi-brassinolide (epi-BL) treatment (20 nM) in an aeroponic system significantly increased the width-to-length ratio (0.045 ± 0.002) compared to the mock-treated plants (0.03 ± 0.002) after 7 weeks, indicating that exogenous epi-BL produces shorter and thicker tubers. In this study we demonstrate the role of BRs in D. polystachya tuber shape, providing insight into the role of plant hormones in yam storage organ development. We found that BRs can influence tuber shape in Chinese yam by regulating the expression of genes involved cell expansion. Our data can help to improve the efficiency of Chinese yam cultivation, which could provide an alternative food source and thus contribute to future food security in Europe.

Combined analysis of mRNA and miRNA reveals the banana potassium absorption regulatory network and validation of miRNA160a

Potassium (K) has an important effect on the growth and development of plants. Banana contains higher K content than many other fruits, and its plant requires more K nutrient in soil. However, the soil in the banana-producing areas in China is generally deficient in K. Therefore, understanding the mechanism of banana K absorption may assist in providing effective strategy to solve this problem. This study used two banana varieties with contrasting K tolerance, 'Guijiao No. 1' (low-K tolerant), and 'Brazilian banana' (low-K sensitive)to investigate K absorption mechanisms in response to low-K stress through miRNA and mRNA sequencing analysis. Under low-K condition, 'Guijiao No.1' showed higher plant height, dry weight, tissue K content and ATPase activity. Analysis of transcription factors showed that they were mainly in the types or classes of MYB, AP-EREBP, bHLH, etc. The sequencing results showed that 'Guijiao No. 1' had 776 differentially expressed genes (DEGs) and 27 differentially expressed miRNAs (DEMs), and 'Brazilian banana' had 71 DEGs and 14 DEMs between normal and low K treatments. RT-qPCR results showed that all miRNAs and mRNAs showed similar expression patterns with RNA-Seq and transcriptome. miRNA regulatory network was constructed by integrated analysis of miRNA-mRNA data. miR160a was screened out as a key miRNA, and preliminary functional validation was performed. Arabidopsis overexpressing miR160a showed reduced tolerance to low K, and inhibited phenotypic traits such as shorter root length, and reduced K accumulation. The overexpressed miR160a had a targeting relationship with ARF10 and ARF16 in Arabidopsis. These results indicate that miR160a may regulate K absorption in bananas through the auxin pathway. This study provides a theoretical basis for further study on the molecular mechanism of banana response to low potassium stress.

Comparative transcriptome analysis during tuberous stem formation in Kohlrabi (B. oleracea var. gongylodes) at early growth periods (seedling stages)

Tuberous stem of kohlrabi is an important agronomic trait, however, the molecular basis of tuberization is poorly understood. To elucidate the tuberization mechanism, we conducted a comparative transcriptomic analysis between kohlrabi and broccoli at 10 and 20 days after germination (DAG) as tuberous stem initiated between these time points. A total of 5580 and 2866 differentially expressed transcripts (DETs) were identified between genotypes (kohlrabi vs. broccoli) and growth stages (10 DAG vs. 20 DAG), respectively, and most of the DETs were down-regulated in kohlrabi. Gene ontology (GO) and KEGG pathway enrichment analyses showed that the DETs between genotypes are involved in cell wall loosening and expansion, cell cycle and division, carbohydrate metabolism, hormone transport, hormone signal transduction and in several transcription factors. The DETs identified in those categories may directly/indirectly relate to the initiation and development of tuberous stem in kohlrabi. In addition, the expression pattern of the hormone synthesis related DETs coincided with the endogenous IAA, IAAsp, GA, ABA, and tZ profiles in kohlrabi and broccoli seedlings, that were revealed in our phytohormone analysis. This is the first report on comparative transcriptome analysis for tuberous stem formation in kohlrabi at early growth periods. The resulting data could provide significant insights into the molecular mechanism underlying tuberous stem development in kohlrabi as well as in other tuberous organ forming crops.

Characterization and bioinformatics analysis of ptc-miR396g-5p in response to drought stress of Paeonia ostii

Drought is one of the main abiotic stress factors affecting yield of Paeonia ostii. In this study, we conducted bioinformatics and differential expression analyses of P. ostii ‘Feng Dan’ ptc-miR396g-5p in leaf samples under different drought stress. ptc-miR396g-5p belongs to the miR396 family. Among the 271 plant species registered in the miRBase database, at least one miR396 member was found in 48 Angiospermae species, 3 in Gymnospermae species, and 1 in Pteridophy. Mature sequence alignment showed that P. ostii ‘Feng Dan’ ptc-miR396g-5p had high sequence similarity with miR396 from other species. Secondary structure prediction showed that the precursor sequence of ‘Feng Dan’ ptc-miR396g-5p could form a stable stem-loop structure, and the mature sequence was located on the 5′ arm of the secondary structure. Phylogenetic tree analysis showed that ‘Feng Dan’ was closely related to 20 species such as Glycine max, Medicago truncatula, Populus trichocarpa, Citrus sinensis, Vitis vinifera, and Theobroma cacao. The predicted target gene of the ‘Feng Dan’ ptc-miR396g-5p encodes a Signal Transducer and Activator of Transcription (STAT) transcription factor. The negative correlation of expression between the miRNA and its target gene was confirmed by qRT-PCR. Our data indicate that ‘Feng Dan’ ptc-miR396g-5p′s expression decreases under drought, leading to an expression increase of the STAT transcription factor.

Roles of Abscisic Acid and Gibberellins in Stem/Root Tuber Development

Root and tuber crops are of great importance. They not only contribute to feeding the population but also provide raw material for medicine and small-scale industries. The yield of the root and tuber crops is subject to the development of stem/root tubers, which involves the initiation, expansion, and maturation of storage organs. The formation of the storage organ is a highly intricate process, regulated by multiple phytohormones. Gibberellins (GAs) and abscisic acid (ABA), as antagonists, are essential regulators during stem/root tuber development. This review summarizes the current knowledge of the roles of GA and ABA during stem/root tuber development in various tuber crops.

Regulatory mechanism of GA3 on tuber growth by DELLA-dependent pathway in yam (Dioscorea opposita)

Endogenous and exogenous GA₃ responses to DoEXP and DoXTH depend on the DoGA20ox1, DoGA3ox1, DoGA2ox3, DoGA2ox4, DoGID1a, and DoDELLA1 to regulate yam tuber growth. Yam tuber undergoes significant alteration in morphogenesis and functions during growth, and gibberellins (GA) are considered potentially important regulators of tuber growth. However, it is little known about the regulation of GA metabolism and GA signaling components genes in tuber growth of yam. In this study, the cloning and expressions of GA₃ level, GA metabolism and signaling genes, and cell wall genes in tuber growth in response to GA₃ and GA biosynthesis inhibitor paclobutrazol (PP₃₃₃) treatments were studied. The contents of GA₃ accumulated at the tuber growth, with the highest levels in the early expansion stage. DoGA20ox1, DoGA3ox1, and four DoGA2ox genes were significantly abundant in the early expansion stage of tuber and gradually declined along with tuber growth. Three DoGID1 and three DoDELLA genes were showed different expression patterns in the early expansion stage of tuber and gradually declined along with tuber growth. Five DoEXP and three DoXTH genes expression levels were higher in the early expansion stage than in other stages. Exogenous GA₃ increased endogenous GA₃ levels, whereas the expression levels of DoGA20ox1, DoGA3ox1, DoGID1a, and DoDELLA1 were down-regulated in the early expansion stage of tuber by GA₃ treatment, DoGA2ox3 and DoGA2ox4 were up-regulated. PP₃₃₃ application exhibited opposite consequences. Thus, a mechanism of GA₃ regulating yam tuber growth by DELLA-dependent pathway is established.

Next-Generation Sequencing Identification and Characterization of MicroRNAs in Dwarfed Citrus Trees Infected With Citrus Dwarfing Viroid in High-Density Plantings

Citrus dwarfing viroid (CDVd) induces stunting on sweet orange trees [Citrus sinensis (L.) Osbeck], propagated on trifoliate orange rootstock [Citrus trifoliata (L.), syn. Poncirus trifoliata (L.) Raf.]. MicroRNAs (miRNAs) are a class of non-coding small RNAs (sRNAs) that play important roles in the regulation of tree gene expression. To identify miRNAs in dwarfed citrus trees, grown in high-density plantings, and their response to CDVd infection, sRNA next-generation sequencing was performed on CDVd-infected and non-infected controls. A total of 1,290 and 628 miRNAs were identified in stem and root tissues, respectively, and among those, 60 were conserved in each of these two tissue types. Three conserved miRNAs (csi-miR479, csi-miR171b, and csi-miR156) were significantly downregulated (adjusted p-value < 0.05) in the stems of CDVd-infected trees compared to the non-infected controls. The three stem downregulated miRNAs are known to be involved in various physiological and developmental processes some of which may be related to the characteristic dwarfed phenotype displayed by CDVd-infected C. sinensis on C. trifoliata rootstock field trees. Only one miRNA (csi-miR535) was significantly downregulated in CDVd-infected roots and it was predicted to target genes controlling a wide range of cellular functions. Reverse transcription quantitative polymerase chain reaction analysis performed on selected miRNA targets validated the negative correlation between the expression levels of these targets and their corresponding miRNAs in CDVd-infected trees. Our results indicate that CDVd-responsive plant miRNAs play a role in regulating important citrus growth and developmental processes that may participate in the cellular changes leading to the observed citrus dwarf phenotype.

Study of Sexual-Linked Genes (OGI and MeGI) on the Performance of Androecious Persimmons (Diospyros kaki Thunb.)

It is reported that the production of floral sexual phenotype in hexaploid monoecious persimmon (Diospyros kaki) is closely related to a pseudogene called OGI, and a short interspersed nuclear element (SINE)-like insertion (named Kali) in the OGI promoter leads to the gene silence. As a result, DNA methylation level of MeGI promoter determines the development of male or female flowers. However, the molecular mechanism in androecious D. kaki, which only bear male flowers, remains elusive. Here, real-time quantitative polymerase chain reaction (RT-qPCR), molecular cloning, and bisulfite PCR sequencing technique were carried out using 87 materials, including 56 androecious resources, 15 monoecious, and 16 gynoecious cultivars, to investigate the performance of OGI and MeGI on the specific androecious type of D. kaki in China. In conclusion, the Kali insertion was exactly located in the OGI promoter region, and the OGI gene and the Kali sequence were existing and conserved in androecious D. kaki. Meanwhile, we also demonstrated that the MeGI gene was widespread in our investigated samples. Ultimately, our result convincingly provided evidence that the low expression of OGI is probably ascribed to the presence of Kali displaying strong methylation in the OGI promoter, and low expression of MeGI, as well as high DNA methylation level, in the promoter was closely connected with the production of male flowers; this result was consistent with the monoecious persimmon model. Our findings provide predominant genetic aspects for investigation into androecious D. kaki, and future perfecting the sex-determining mechanisms in persimmon.

Hormonal and transcriptional analyses provides new insights into the molecular mechanisms underlying root thickening and isoflavonoid biosynthesis in Callerya speciosa (Champ. ex Benth.) Schot

Callerya speciosa (Champ. ex Benth.) Schot is a traditional Chinese medicine characterized by tuberous roots as the main organ of isoflavonoid accumulation. Root thickening and isoflavonoid accumulation are two major factors for yield and quality of C. speciosa. However, the underlying mechanisms of root thickening and isoflavonoid biosynthesis have not yet been elucidated. Here, integrated morphological, hormonal and transcriptomic analyses of C. speciosa tuberous roots at four different ages (6, 12, 18, 30 months after germination) were performed. The growth cycle of C. speciosa could be divided into three stages: initiation, rapid-thickening and stable-thickening stage, which cued by the activity of vascular cambia. Endogenous changes in phytohormones were associated with developmental changes during root thickening. Jasmonic acid might be linked to the initial development of tuberous roots. Abscisic acid seemed to be essential for tuber maturation, whereas IAA, cis-zeatin and gibberellin 3 were considered essential for rapid thickening of tuberous roots. A total of 4337 differentially expressed genes (DEGs) were identified during root thickening, including 15 DEGs participated in isoflavonoid biosynthesis, and 153 DEGs involved in starch/sucrose metabolism, hormonal signaling, transcriptional regulation and cell wall metabolism. A hypothetical model of genetic regulation associated with root thickening and isoflavonoid biosynthesis in C. speciosa is proposed, which will help in understanding the underlying mechanisms of tuberous root formation and isoflavonoid biosynthesis.

Tumorous Stem Development of Brassica Juncea: A Complex Regulatory Network of Stem Formation and Identification of Key Genes in Glucosinolate Biosynthesis

Stem mustard is a stem variety of mustard, an important Brassica vegetable. The formation and development of the tumorous stem, which is the key organ for the direct yield and quality, is a complex biological process involving morphogenesis, material accumulation and gene regulation. In this study, we demonstrated through anatomical studies that stem swelling is mainly dependent on the increase in the number of cells and the volume of parenchyma cells in the cortex and pith. To further understand transcript and metabolic changes during stem swelling, we obtained 27,901 differentially expressed genes, of which 671 were specifically detected using transcriptome sequencing technology in all four stages of stem swelling. Functional annotation identified enrichment for genes involved in photosynthesis, energy metabolism, cell growth, sulfur metabolism and glucosinolate biosynthesis. Glucosinolates are a group of nitrogen- and sulfur-containing secondary metabolites, which largely exist in the Cruciferous vegetables. HPLC analysis of the contents and components of glucosinolates in four different stem development stages revealed eight glucosinolates, namely, three aliphatic glucosinolates (sinigrin, glucoalyssin and gluconapin), four indole glucosinolates (4-hydroxyglucobrassicin, glucobrassicin, 4-methoxyglucobrassicin and neoglucobrassicin) and one aromatic glucosinolate (gluconasturtiin). All these types of glucosinolates showed a significant downward trend during the stem swelling period. The content of aliphatic glucosinolates was the highest, with sinigrin being the main component. In addition, qPCR was used to validate the expression of nine genes involved in glucosinolate biosynthesis. Most of these genes were down-regulated during stem swelling in qPCR, which is consistent with transcriptome data. These data provide a basic resource for further molecular and genetic research on Brassica juncea.