Proteomic changes during tuber dormancy release process revealed by iTRAQ quantitative proteomics in potato

Proteomic insights to decipher nanoparticle uptake, translocation, and intercellular mechanisms in plants

Advent of proteomic techniques has made it possible to identify a broad spectrum of proteins in living systems. Studying the impact of nanoparticle (NP)-mediated plant protein responses is an emerging field. NPs are continuously being released into the environment and directly or indirectly affect plant's biochemistry. Exposure of plants to NPs, especially crops, poses a significant risk to the food chain, leading to changes in underlying metabolic processes. Once absorbed by plants, NPs interact with cellular proteins, thereby inducing changes in plant protein patterns. Based on the reactivity, properties, and translocation of nanoparticles, NPs can interfere with proteins involved in various cellular processes in plants such as energy regulation, redox metabolism, and cytotoxicity. Such interactions of NPs at the subcellular level enhance ROS scavenging activity, especially under stress conditions. Although higher concentrations of NPs induce ROS production and hinder oxidative mechanisms under stress conditions, NPs also mediate metabolic changes from fermentation to normal cellular processes. Although there has been lots of work conducted to understand the different effects of NPs on plants, the knowledge of proteomic responses of plants toward NPs is still very limited. This review has focused on the multi-omic analysis of NP interaction mechanisms with crop plants mainly centering on the proteomic perspective in response to both stress and non-stressed conditions. Furthermore, NP-specific interaction mechanisms with the biological pathways are discussed in detail.

Recent advances in plant translational genomics for crop improvement

The growing population, climate change, and limited agricultural resources put enormous pressure on agricultural systems. A plateau in crop yields is occurring and extreme weather events and urbanization threaten the livelihood of farmers. It is imperative that immediate attention is paid to addressing the increasing food demand, ensuring resilience against emerging threats, and meeting the demand for more nutritious, safer food. Under uncertain conditions, it is essential to expand genetic diversity and discover novel crop varieties or variations to develop higher and more stable yields. Genomics plays a significant role in developing abundant and nutrient-dense food crops. An alternative to traditional breeding approach, translational genomics is able to improve breeding programs in a more efficient and precise manner by translating genomic concepts into practical tools. Crop breeding based on genomics offers potential solutions to overcome the limitations of conventional breeding methods, including improved crop varieties that provide more nutritional value and are protected from biotic and abiotic stresses. Genetic markers, such as SNPs and ESTs, contribute to the discovery of QTLs controlling agronomic traits and stress tolerance. In order to meet the growing demand for food, there is a need to incorporate QTLs into breeding programs using marker-assisted selection/breeding and transgenic technologies. This chapter primarily focuses on the recent advances that are made in translational genomics for crop improvement and various omics techniques including transcriptomics, metagenomics, pangenomics, single cell omics etc. Numerous genome editing techniques including CRISPR Cas technology and their applications in crop improvement had been discussed.

Comparative Proteomics of Potato Cultivars with a Variable Dormancy Period

The control of the duration of the dormancy phase is a significant challenge in the potato industry and for seed producers. However, the proteome landscape involved in the regulation of the length of the dormancy period over potato cultivars remains largely unexplored. In this study, we performed for the first time a comparative proteome profiling of potato cultivars with differential duration of tuber dormancy. More specifically, the proteome profiling of Agata, Kennebec and Agria commercial potato varieties with short, medium and medium-long dormancy, respectively, was assessed at the endodormancy stage using high-resolution two-dimensional electrophoresis (2-DE) coupled to reversed-phase liquid chromatography–tandem mass spectrometry (LC-TripleTOF MS/MS). A total of 11 proteins/isoforms with statistically significant differential abundance among cultivars were detected on 2-DE gels and confidently identified by LC-TripleTOF MS/MS. Identified proteins have known functions related to tuber development, sprouting and the oxylipins biosynthesis pathway. Fructokinase, a mitochondrial ADP/ATP carrier, catalase isozyme 2 and heat shock 70 kDa were the proteins with the strongest response to dormancy variations. To the best of our knowledge, this study reports the first candidate proteins underlying variable dormancy length in potato cultivars.

Multi-omics analysis reveals the molecular changes accompanying heavy-grazing-induced dwarfing of Stipa grandis

Heavy grazing significantly reduces Stipa grandis growth. To enhance our understanding of plant responses to heavy grazing, we conducted transcriptomic, proteomic, and metabolic analyses of the leaves of non-grazed plants (NG) and heavy-grazing-induced dwarf plants (HG) of S. grandis. A total of 101 metabolites, 167 proteins, and 1,268 genes differed in abundance between the HG and NG groups. Analysis of Kyoto Encyclopedia of Genes and Genomes pathways among differentially accumulated metabolites (DAMs) revealed that the most enriched pathways were flavone and flavonol biosynthesis, tryptophan metabolism, and phenylpropanoid biosynthesis. An integrative analysis of differentially expressed genes (DEGs) and proteins, and DAMs in these three pathways was performed. Heavy-grazing-induced dwarfism decreased the accumulation of DAMs enriched in phenylpropanoid biosynthesis, among which four DAMs were associated with lignin biosynthesis. In contrast, all DAMs enriched in flavone and flavonol biosynthesis and tryptophan metabolism showed increased accumulation in HG compared with NG plants. Among the DAMs enriched in tryptophan metabolism, three were involved in tryptophan-dependent IAA biosynthesis. Some of the DEGs and proteins enriched in these pathways showed different expression trends. The results indicated that these pathways play important roles in the regulation of growth and grazing-associated stress adaptions of S. grandis. This study enriches the knowledge of the mechanism of heavy-grazing-induced growth inhibition of S. grandis and provides valuable information for restoration of the productivity in degraded grassland.

Snakin-2 interacts with cytosolic glyceraldehyde-3-phosphate dehydrogenase 1 to inhibit sprout growth in potato tubers

The potato tuber is the main nutrient supply and reproductive organ; however, tuber sprouting can reduce its commercial value. Snakin-2 (StSN2) was first reported as an antimicrobial peptide that positively regulates potato disease resistance. Our recent study suggested StSN2 overexpression inhibited sprout growth, while the sprouting process was accelerated in StSN2 RNAi lines. Cytoplasmic glyceraldehyde-3- phosphate dehydrogenase 1 (StGAPC1) was identified as a candidate protein that interacts with StSN2 by coimmunoprecipitation/mass spectrometry (CoIP/MS) experiments. Here, we report that the expression levels of StSN2 and StGAPC1 decreased during sprouting compared with dormancy. Coexpression of StSN2 and StGAPC1 in bud eyes and apical buds was verified by immunofluorescence analysis of paraffin sections. In addition, interaction of StSN2 and StGAPC1 was confirmed by yeast two-hybrid, coimmunoprecipitation and split luciferase complementation assays. Overexpression of StGAPC1 depressed sprout growth, which is similar to the function of StSN2, and StSN2- and StGAPC1-overexpressing lines showed decreased glucose, fructose and galactose content. The interaction of StSN2 and StGAPC1 enhanced StGAPC1 activity and decreased its oxidative modification to inhibit sprout growth. Our results suggest that StSN2 plays a regulatory role in tuber sprout growth through interaction with StGAPC1.

Applications of Multi-Omics Technologies for Crop Improvement

Multiple "omics" approaches have emerged as successful technologies for plant systems over the last few decades. Advances in next-generation sequencing (NGS) have paved a way for a new generation of different omics, such as genomics, transcriptomics, and proteomics. However, metabolomics, ionomics, and phenomics have also been well-documented in crop science. Multi-omics approaches with high throughput techniques have played an important role in elucidating growth, senescence, yield, and the responses to biotic and abiotic stress in numerous crops. These omics approaches have been implemented in some important crops including wheat (Triticum aestivum L.), soybean (Glycine max), tomato (Solanum lycopersicum), barley (Hordeum vulgare L.), maize (Zea mays L.), millet (Setaria italica L.), cotton (Gossypium hirsutum L.), Medicago truncatula, and rice (Oryza sativa L.). The integration of functional genomics with other omics highlights the relationships between crop genomes and phenotypes under specific physiological and environmental conditions. The purpose of this review is to dissect the role and integration of multi-omics technologies for crop breeding science. We highlight the applications of various omics approaches, such as genomics, transcriptomics, proteomics, metabolomics, phenomics, and ionomics, and the implementation of robust methods to improve crop genetics and breeding science. Potential challenges that confront the integration of multi-omics with regard to the functional analysis of genes and their networks as well as the development of potential traits for crop improvement are discussed. The panomics platform allows for the integration of complex omics to construct models that can be used to predict complex traits. Systems biology integration with multi-omics datasets can enhance our understanding of molecular regulator networks for crop improvement. In this context, we suggest the integration of entire omics by employing the "phenotype to genotype" and "genotype to phenotype" concept. Hence, top-down (phenotype to genotype) and bottom-up (genotype to phenotype) model through integration of multi-omics with systems biology may be beneficial for crop breeding improvement under conditions of environmental stresses.

Quantitative phosphoproteomics analysis reveals that protein modification and sugar metabolism contribute to sprouting in potato after BR treatment

Brassinosteroids (BRs), a new class of steroid hormones, are involved in the regulation of plant cell elongation and seed germination. Nevertheless, the molecular mechanism of the effect of BRs on tuber sprouting remains largely unknown. In this study, quantitative phosphoproteomics was employed to investigate the protein phosphorylation changes in sprouting induced by BRs. Our results showed that BRs accelerated the conversion of starch into soluble sugar in tubers. A functional enrichment cluster analysis suggested that the "amino acid metabolism pathway" was upregulated and that "plant hormone signal transduction and protein export" were downregulated. BR treatment also changed the phosphorylation of proteins involved in the BR, ABA, starch and sugar signal transduction pathways, such as serine/threonine-protein kinase (BSK), 14-3-3, alpha-glucan water dikinase (GWD), sucrose-phosphate synthase (SPS), sucrose synthase (SS) and alkaline/neutral invertase (A/N-INV). These results shed more light on the pattern of protein phosphorylation in BR promoting potato sprouting.

Differential protein analysis of Heracleum moellendorffii Hance seeds during stratification

Heracleum moellendorffii Hance is a medicinal vegetable species, and the seed dormancy of this species has caused many agricultural problems. One stratification technique involves alternating layers of seeds and substrate to allow post-ripening of dormant seeds under appropriate environmental conditions and to release dormancy. Non-stratified seeds (NS), cotyledon-stage-embryo seeds (CS) and germinated seeds (GS) represent key stages of H. moellendorffii seeds during stratification. To better understand the breaking of dormancy caused by stratification, tandem mass tag (TMT) mass spectrometry (MS)/MS was used to detect proteins among NS, CS and GS. A total of 876 proteins were identified, which were subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. The results showed that carbohydrate metabolic processes, responses to stress and ribosome biogenesis were the main biological processes. The changes in protein accumulation were validated by qRT-PCR. The results showed that starch, sucrose, pyruvate and fatty acid metabolism played significant roles and that the contents of stored substances were gradually degraded during stratification. This study provides a theoretical basis in terms of proteomics for exploring the post-ripening and germination of H. moellendorffii seeds.

iTRAQ-based mitochondrial proteome analysis of the molecular mechanisms underlying postharvest senescence of Zizania latifolia

To explore the molecular mechanisms underlying postharvest senescence of Zizania latifolia, the changes in the mitochondrial proteome of plants treated with or without (control) 1-methyleyelopropene and ethylene during storage at room temperature for 0, 3 and 6 days were investigated using isobaric tags for relative and absolute quantitation (iTRAQ) labeling combined with two-dimensional liquid chromatography-tandem mass spectrometry. A total of 1,390 proteins with two or more peptides were identified, of which 211 showed a significant (p < .05) change (at least twofold) in relative abundance. Monitoring the parallel reaction validated the reliability and accuracy of the iTRAQ results. Bioinformatics and functional analysis of these differentially expressed proteins (DEPs) revealed that postharvest senescence of Z. latifolia could be attributed to (a) strengthened pentose phosphate pathway, (b) imbalanced protein, amino acid, organic acid, and fatty acid metabolism, (c) disordered energy homeostasis, (d) exacerbated oxidative damage, (e) RNA degradation, (f) activation of the Ca²⁺ , mitogen-activated protein kinase, and jasmonic acid signaling pathways, (g) programed cell death, (h) excessive biosynthesis of secondary metabolites, or (i) degradation of cell structure. Our findings provide integrated insight into the molecular mechanisms of postharvest senescence during storage as well as the DEPs that show promise as targets for controlling senescence-induced quality deterioration of Z. latifolia. PRACTICAL APPLICATIONS: Postharvest senescence is the most important factor that causes fast quality deterioration of Zizania latifolia. The understanding of the processes leading to postharvest senescence of Z. latifolia is essential in enhancing the commercial value and extending the shelf life of the product. It is currently believed that the mitochondrial metabolism is closely related to postharvest senescence. For this, the changes of proteome in Z. latifolia mitochondria treated with or without (control) 1-MCP and ETH during storage at room temperature were investigated. Results showed that a variety of physiobiochemical responses occur during postharvest senescence of Z. latifolia. 1-MCP treatment significantly inhibited the changes of these physiobiochemical processes, finally, retarding the postharvest senescence of Z. latifolia. ETH treatment had opposite effects on proteome changes compared with 1-MCP treatment. Taken together, these results enrich the understanding of the molecular mechanisms of postharvest senescence of Z. latifolia.

Silencing of α-amylase StAmy23 in potato tuber leads to delayed sprouting

Potato tuber dormancy is critical for the postharvest quality. The supply of carbohydrates is considered as one of the important factors controlling the rate of potato tuber sprouting. Starch is the major carbohydrate reserve in potato tuber, but very little is known about the specific starch degrading enzymes responsible for controlling tuber dormancy and sprouting. In this study, we demonstrate that an α-amylase gene StAmy23 is involved in starch breakdown and regulation of tuber dormancy. Silencing of StAmy23 delayed tuber sprouting by one to two weeks compared with the control. This phenotype is accompanied by reduced levels of reducing sugars and elevated levels of malto-oligosaccharides in tuber cortex and pith tissue below the bud eye of StAmy23-deficient potato tubers. Changes in soluble sugars is accompanied by a slight variation of phytoglycogen structure and starch granule size. Our results suggest that StAmy23 may stimulate sprouting by hydrolyzing soluble phytoglycogen to ensure supply of sugars during tuber dormancy.

Proteome-Level Analysis of Metabolism- and Stress-Related Proteins during Seed Dormancy and Germination in Gnetum parvifolium

Gnetum parvifolium is a rich source of materials for traditional medicines, food, and oil, but little is known about the mechanism underlying its seed dormancy and germination. In this study, we analyzed the proteome-level changes in its seeds during germination using isobaric tags for relative and absolute quantitation. In total, 1,040 differentially expressed proteins were identified, and cluster analysis revealed the distinct time points during which signal transduction and oxidation-reduction activity changed. Gene Ontology analysis showed that "carbohydrate metabolic process" and "response to oxidative stress" were the main enriched terms. Proteins associated with starch degradation and antioxidant enzymes were important for dormancy-release, while proteins associated with energy metabolism and protein synthesis were up-regulated during germination. Moreover, protein-interaction networks were mainly associated with heat-shock proteins. Furthermore, in accord with changes in the energy metabolism- and antioxidant-related proteins, indole-3-acetic acid, Peroxidase, and soluble sugar content increased, and the starch content decreased in almost all six stages of dormancy and germination analyzed (S1-S6). The activity of superoxide dismutase, abscisic acid, and malondialdehyde content increased in the dormancy stages (S1-S3) and then decreased in the germination stages (S4-S6). Our results provide new insights into G. parvifolium seed dormancy and germination at the proteome and physiological levels, with implications for improving seed propagation.

Comparative proteomic analysis provides insight into a complex regulatory network of taproot formation in radish (Raphanus sativus L.)

The fleshy taproot of radish is an important storage organ determining its yield and quality. Taproot thickening is a complex developmental process in radish. However, the molecular mechanisms governing this process remain unclear at the proteome level. In this study, a comparative proteomic analysis was performed to analyze the proteome changes at three developmental stages of taproot thickening using iTRAQ approach. In total, 1862 differentially expressed proteins (DEPs) were identified from 6342 high-confidence proteins, among which 256 up-regulated proteins displayed overlapped accumulation in S1 (pre-cortex splitting stage) vs. S2 (cortex splitting stage) and S1 vs. S3 (expanding stage) pairs, whereas 122 up-regulated proteins displayed overlapped accumulation in S1 vs. S3 and S2 vs. S3 pairs. Gene Ontology (GO) and pathway enrichment analysis showed that these DEPs were mainly involved in several processes such as "starch and sucrose metabolism", "plant hormone signal transduction", and "biosynthesis of secondary metabolites". A high concordance existed between iTRAQ and RT-qPCR at the mRNA expression levels. Furthermore, association analysis showed that 187, 181, and 96 DEPs were matched with their corresponding differentially expressed genes (DEGs) in S1 vs. S2, S1 vs. S3, and S2 vs. S3 comparison, respectively. Notably, several functional proteins including cell division cycle 5-like protein (CDC5), expansin B1 (EXPB1), and xyloglucan endotransglucosylase/hydrolase protein 24 (XTH24) were responsible for cell division and expansion during radish taproot thickening process. These results could facilitate a better understanding of the molecular mechanism underlying taproot thickening, and provide valuable information for the identification of critical genes/proteins responsible for taproot thickening in root vegetable crops.

Genome-Wide Analysis of Long Non-Coding RNAs in Potato and Their Potential Role in Tuber Sprouting Process

Sprouting is a key factor affecting the quality of potato tubers. The present study aimed to compare the differential expression of long non-coding RNAs (lncRNAs) in the apical meristem during the dormancy release and sprouting stages by using lncRNA sequencing. Microscopic observations and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed the changes in the morphology and expression of lncRNAs in potato tubers during sprouting. Meristematic cells of potato tuber apical buds divided continuously and exhibited vegetative cone bulging and vascularisation. In all, 3175 lncRNAs were identified from the apical buds of potato tubers, among which 383 lncRNAs were up-regulated and 340 were down-regulated during sprouting. The GO enrichment analysis revealed that sprouting mainly influenced the expression of lncRNAs related to the cellular components of potato apical buds (e.g., cytoplasm and organelles) and cellular metabolic processes. The KEGG enrichment analysis also showed significant enrichment of specific metabolic pathways. In addition, 386 differentially expressed lncRNAs during sprouting were identified as putative targets of 235 potato miRNAs. Quantitative real-time polymerase chain reaction results agreed with the sequencing data. Our study provides the first systematic study of numerous lncRNAs involved in the potato tuber sprouting process and lays the foundation for further studies to elucidate their precise functions.

Comparative Morphology, Transcription, and Proteomics Study Revealing the Key Molecular Mechanism of Camphor on the Potato Tuber Sprouting Effect

Sprouting regulation in potato tubers is important for improving commercial value and producing new plants. Camphor shows flexible inhibition of tuber sprouting and prolongs the storage period of potato, but its underlying mechanism remains unknown. The results of the present study suggest that camphor inhibition caused bud growth deformities and necrosis, but after moving to more ventilated conditions, new sprouts grew from the bud eye of the tuber. Subsequently, the sucrose and fructose contents as well as polyphenol oxidase (PPO) activity were assessed after camphor inhibition. Transcription and proteomics data from dormancy (D), sprouting (S), camphor inhibition (C), and recovery sprouting (R) samples showed changes in the expression levels of approximately 4000 transcripts, and 700 proteins showed different abundances. KEGG (Kyoto encyclopaedia of genes and genomes) pathway analysis of the transcription levels indicated that phytohormone synthesis and signal transduction play important roles in tuber sprouting. Camphor inhibited these processes, particularly for gibberellic acid, brassinosteroids, and ethylene, leading to dysregulation of physiological processes such as cutin, suberine and wax biosynthesis, fatty acid elongation, phenylpropanoid biosynthesis, and starch and sucrose metabolism, resulting in bud necrosis and prolonged storage periods. The KEGG pathway correlation between transcripts and proteins revealed that terpenoid backbone biosynthesis and plant-pathogen interaction pathways showed significant differences in D vs. S samples, but 13 pathways were remarkably different in the D vs. C groups, as camphor inhibition significantly increased both the transcription levels and protein abundance of pathogenesis-related protein PR-10a (or STH-2), the pathogenesis-related P2-like precursor protein, and the kirola-like protein as compared to sprouting. In recovery sprouting, these genes and proteins were decreased at both the transcriptional level and in protein abundance. It was important to find that the inhibitory effect of camphor on potato tuber sprout was reversible, revealing the action mechanism was similar to resistance to pathogen infection. The present study provides a theoretical basis for the application of camphor in prolonging seed potato storage.

Proteomic analysis of peel browning of 'Nanguo' pears after low-temperature storage

BACKGROUND

Postharvest ripening of the 'Nanguo' pear (Pyrus ussuriensis Maxim.) can be impeded by low-temperature storage. However, pears after long-term refrigeration are prone to peel browning when returned to room temperature conditions. This study investigated the browning mechanism of 'Nanguo' pear stored at a low temperature by analysing the differentially expressed proteins between healthy fruit and fruit with peel browning.

RESULTS

The results showed that 181 proteins underwent statistically significant changes. A categorisation of the disparately accumulated proteins was performed using gene ontology annotation. The results showed that the 'metabolic process', 'cellular process', 'catalytic activity', and 'binding' proteins were the most affected after low-temperature storage. Further analysis revealed that the differentially expressed proteins, which are related to peel browning, are primarily involved in the phenylpropanoid pathway, linoleic acid pathways, fatty acid biosynthesis pathway, glutathione metabolism pathway, photosynthesis pathway, oxidative phosphorylation pathway, and glycolysis pathway.

CONCLUSION

This study reveals that there are variations in key proteins in 'Nanguo' pear after low-temperature storage, and the identification of these proteins will be valuable in future functional genomics studies, as well as provide protein resources that can be used in the efforts to improve pear quality. © 2016 Society of Chemical Industry.

Integrated analysis of multiomic data reveals the role of the antioxidant network in the quality of sea buckthorn berry

Berries of sea buckthorn, known as the "king of vitamin C," are abundant in antioxidants, have attractive colors, and are an excellent material with which to study the relationships between berry color, antioxidants, and berry quality. No study has yet determined the molecular basis of the relationship between sea buckhorn berries and their color and antioxidant levels. By using RNA-seq, LC-MS/MS, and LC/GC-MS technology and selecting red (darkest colored) and yellow (lightest colored) sea buckthorn berries at different development stages, this study showed that the red and yellow berry resulted from a higher ratio of lycopene to β-carotene and of β-carotene to lycopene content, respectively. The uronic acid pathway-a known animal pathway-in ascorbic acid synthesis was found in sea buckthorn berries, and the higher expression of UDP-glucuronosyltransferase in red berries was consistent with the higher content of ascorbic acid. In summary, multiomic data showed that the color of sea buckthorn berries is mainly determined by β-carotene and lycopene; red sea buckthorn berries were richer than yellow berries in antioxidants, such as carotenoids, flavonoids, and ascorbic acid; and the animal pathway might be operating in sea buckthorn.-He, C., Zhang, G., Zhang, J., Zeng, Y., Liu, J. Integrated analysis of multiomic data reveals the role of the antioxidant network in the quality of sea buckthorn berry.