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. 2020 Nov 18;21(22):8700.
doi: 10.3390/ijms21228700.

Integrated Proteo-Transcriptomic Analyses Reveal Insights into Regulation of Pollen Development Stages and Dynamics of Cellular Response to Apple Fruit Crinkle Viroid (AFCVd)-Infection in Nicotiana tabacum

Affiliations

Integrated Proteo-Transcriptomic Analyses Reveal Insights into Regulation of Pollen Development Stages and Dynamics of Cellular Response to Apple Fruit Crinkle Viroid (AFCVd)-Infection in Nicotiana tabacum

Ankita Shrestha et al. Int J Mol Sci. .

Abstract

Tobacco (Nicotiana tabacum) pollen is a well-suited model for studying many fundamental biological processes owing to its well-defined and distinct development stages. It is also one of the major agents involved in the transmission of infectious viroids, which is the primary mechanism of viroid pathogenicity in plants. However, some viroids are non-transmissible and may be possibly degraded or eliminated during the gradual process of pollen development maturation. The molecular details behind the response of developing pollen against the apple fruit crinkle viroid (AFCVd) infection and viroid eradication is largely unknown. In this study, we performed an integrative analysis of the transcriptome and proteome profiles to disentangle the molecular cascade of events governing the three pollen development stages: early bicellular pollen (stage 3, S3), late bicellular pollen (stage 5, S5), and 6 h-pollen tube (PT6). The integrated analysis delivered the molecular portraits of the developing pollen against AFCVd infection, including mechanistic insights into the viroid eradication during the last steps of pollen development. The isobaric tags for label-free relative quantification (iTRAQ) with digital gene expression (DGE) experiments led us to reliably identify subsets of 5321, 5286, and 6923 proteins and 64,033, 60,597, and 46,640 expressed genes in S3, S5, and PT6, respectively. In these subsets, 2234, 2108 proteins and 9207 and 14,065 mRNAs were differentially expressed in pairwise comparisons of three stages S5 vs. S3 and PT6 vs. S5 of control pollen in tobacco. Correlation analysis between the abundance of differentially expressed mRNAs (DEGs) and differentially expressed proteins (DEPs) in pairwise comparisons of three stages of pollen revealed numerous discordant changes in mRNA/protein pairs. Only a modest correlation was observed, indicative of divergent transcription, and its regulation and importance of post-transcriptional events in the determination of the fate of early and late pollen development in tobacco. The functional and enrichment analysis of correlated DEGs/DEPs revealed the activation in pathways involved in carbohydrate metabolism, amino acid metabolism, lipid metabolism, and cofactor as well as vitamin metabolism, which points to the importance of these metabolic pathways in pollen development. Furthermore, the detailed picture of AFCVd-infected correlated DEGs/DEPs was obtained in pairwise comparisons of three stages of infected pollen. The AFCVd infection caused the modulation of several genes involved in protein degradation, nuclear transport, phytohormone signaling, defense response, and phosphorylation. Intriguingly, we also identified several factors including, DNA-dependent RNA-polymerase, ribosomal protein, Argonaute (AGO) proteins, nucleotide binding proteins, and RNA exonucleases, which may plausibly involve in viroid stabilization and eradication during the last steps of pollen development. The present study provides essential insights into the transcriptional and translational dynamics of tobacco pollen, which further strengthens our understanding of plant-viroid interactions and support for future mechanistic studies directed at delineating the functional role of candidate factors involved in viroid elimination.

Keywords: AFCVd propagation and eradication; Nicotiana tabacum; Proteome; RNA sequencing; RT qPCR; male gametophyte; viroid degradation; viroid replication.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Venn diagram of transcriptome and proteome. Number of transcripts (A) and proteins (B) identified in stage 3 (CT_S3), stage 5 (CT_S5), and pollen tube after 6 hours of germination (CT_PT6) in control samples.
Figure 2
Figure 2
Histogram of Gene Ontology (GO) classification of correlated differentially expressed mRNAs/differentially expressed proteins (DEGs/DEPs) in stage-specific comparison in control (A) and AFCVd-infected (B) pollen. The results are summarized in three main categories: biological process, cellular component, and molecular function. The x-axis indicates subcategories; right y-axis indicates number of genes in a category. UR: upregulated, DR: downregulated.
Figure 3
Figure 3
GO functional enrichment analysis of correlated DEGs/DEPs in pairwise comparison of S5 vs. S3 (A) and PT6 vs. S5 (B) of control male gametophyte of tobacco. The y-axis indicates gene functions, and the x-axis indicates gene ratios. The size of the dots represents the degree of enrichment and their color indicates degree of statistical significance.
Figure 4
Figure 4
GO functional enrichment analysis of correlated DEGs/DEPs in pairwise comparisons of S5 vs. S3 (A) and PT6 vs. S5 (B) of AFCVd-infected male gametophyte of tobacco. The y-axis indicates gene functions, and the x-axis indicates gene ratios. The size of dots represents the degree of enrichment and their color indicates the degree of statistical significance.
Figure 5
Figure 5
Overview of the MapMan visualization of correlated DEGs/DEPs in pairwise comparisons of S5 vs. S3 (A) and PT6 vs. S5 (B) of healthy (control) male gametophyte of tobacco. The log2 fold changes of significantly modulated cor-DEGs/DEPs were imported and visualized in MapMan. Signals colored red and green represent a decrease or increase in transcript abundance in the pairwise comparison sets. The scale used for coloration of the signals (log2 ratios) is shown on the top right.
Figure 6
Figure 6
Overview of the MapMan visualization of correlated DEGs/DEPs in pairwise comparison of S5 vs. S3 (A) and PT6 vs. S5 (B) of AFCVd-infected male gametophyte of tobacco. The log2 fold changes of significantly cor-DEGs/DEPs were imported and visualized in MapMan. Signals colored red and green represent a decrease or increase in transcript abundance in the pairwise comparison sets of three AFCVd-infected stages. The scale used for coloration of the signals (log2 ratios) is shown on the top right.
Figure 7
Figure 7
Cluster analysis of associated correlated DEGs/DEPs at transcript and protein levels in pairwise comparison of control and AFCVd (AI) samples of S3, S5, and PT6. Each row in the graph represents a protein/mRNA, and each column in the graph represents the log2 transformed average FPKM value of DEGs of two biological replicates (n = 2) and log2 transformed average iTRAQ value of corresponding DEPs of three biological replicates (n = 3). Expression differences are shown in different colors; red indicates up-regulation, while blue indicates down-regulation. The color scale of the heat map ranges from saturated blue (value, −2.0) to saturated red (value, 2.0) in the natural logarithmic scale.
Figure 8
Figure 8
Validation of expression patterns of differentially expressed genes by RT-qPCR. Graph showing fold change of gene expression in pairwise comparison of stage 5 vs. stage 3 (A) and stage PT6 vs. stage 5 (B) of three developmental stages of control and stage 5 vs. stage 3 (C) and stage PT6 vs. stage 5 (D) of AFCVd-infected three developmental stages of male gametophyte of tobacco. AMYL: alpha-amylase; APT1: aberrant pollen transmission 1; SYNAP: synaptotagmin C2 membrane targeting protein; SEC13: protein transport SEC13-like protein; GID1L2: gibberellin receptor; PYRD2: pyruvate decarboxylase 2; RPL5: 50S Ribosomal protein L5; EXO: RNA exonuclease; SSInP: single-stranded-interacting protein 1; DRP: DNA-directed RNA polymerase; NABP: nucleic acid binding protein-K Homology domain; NTF2: nuclear transport factor 2; AGO4: argonaute 4-like protein. The qRT-PCR data (green bars) are expressed as the mean values of three experimental replicates from three independent experiments, with error bars depicting the standard error. The RNA-seq data (orange bars) are also shown for comparison.

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