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. 2014 Nov 5;15(1):957.
doi: 10.1186/1471-2164-15-957.

De-novo assembly of mango fruit peel transcriptome reveals mechanisms of mango response to hot water treatment

Neta Luria, Noa Sela, Mor Yaari, Oleg Feygenberg, Ilana Kobiler, Amnon Lers, Dov Prusky  1
Affiliations

De-novo assembly of mango fruit peel transcriptome reveals mechanisms of mango response to hot water treatment

Neta Luria et al. BMC Genomics. .

Abstract

Background: The mango belongs to the genus Mangifera, consisting of numerous tropical fruiting trees in the flowering plant family, Anacardiaceae. Postharvest treatment by hot water brushing (HWB) for 15-20 s was introduced commercially to improve fruit quality and reduce postharvest disease. This treatment enabled successful storage for 3-4 weeks at 12°C, with improved color and reduced disease development, but it enhanced lenticel discoloration on the fruit peel. We investigated global gene expression induced in fruit peel by HWB treatment, and identified key genes involved in mechanisms potentially associated with fruit resistance to pathogens, peel color improvement, and development of lenticel discoloration; this might explain the fruit's phenotypic responses.

Results: The mango transcriptome assembly was created and characterized by application of RNA-seq to fruit-peel samples. RNA-seq-based gene-expression profiling identified three main groups of genes associated with HWB treatment: 1) genes involved with biotic and abiotic stress responses and pathogen-defense mechanisms, which were highly expressed; 2) genes associated with chlorophyll degradation and photosynthesis, which showed transient and low expression; and 3) genes involved with sugar and flavonoid metabolism, which were highly expressed.

Conclusions: We describe a new transcriptome of mango fruit peel of cultivar Shelly. The existence of three main groups of genes that were differentially expressed following HWB treatment suggests a molecular basis for the biochemical and physiological consequences of the postharvest HWB treatment, including resistance to pathogens, improved color development, and occurrence of lenticel discoloration.

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Figures

Figure 1
Figure 1
Characterization of de-novo assembly of mango transcriptome. All distinct gene sequences that had BLAST annotations within the non-redundant protein database with a cut-off E-value ≤10-5 were analyzed for: (A) transcript length; (B) E-value distribution; and (C) species distribution.
Figure 2
Figure 2
Gene ontology (GO) classification of the Mangifera indica transcripts. Out of 57,544 transcripts, 28,317 sequences were annotated within the GO database into three main categories: cellular component, molecular function, and biological process. The y-axis indicates the number of transcripts; the x-axis indicates the GO category.
Figure 3
Figure 3
Venn diagram showing number of overlapping and non-overlapping differentially expressed mango fruit genes at different sampling times after HWB treatment. (A) All differentially expressed genes; (B) differentially expressed genes that were upregulated; (C) differentially expressed genes that were downregulated. Fruit tissue was sampled at 0, 4, 17 and 48 h after the HWB treatment, and compared with that of untreated fruits sampled at the same time points.
Figure 4
Figure 4
Heat-map diagram showing the five clusters of differentially expressed genes following HWB treatment. (A) Plots of the expression profiles of 1,225 differentially expressed genes. Gray lines mark the various gene profiles; the green, red, blue, pink and light-blue lines represent the average expression profiles of clusters 1–5, respectively. (B) Heat map showing relative expression of 1,225 fruit genes at the four sampling times (0, 4, 17 and 48 h). Color key represents relative expression on a log 2 scale.
Figure 5
Figure 5
Validation of RNA-seq results by means of qRT-PCR. Ten differentially expressed genes (two from each of clusters 1 to 5) were examined by RNA-seq and qRT-PCR at four different time points after HWB treatment: A, B (cluster 1); C, D (cluster 2); E, F (cluster 3); G, H (cluster 4); and I, J (cluster 5). Values were normalized to the values obtained with untreated mango fruit samples at 0 h and the proportional fold-change (FC) was calculated. Expression data are means of two replicates.
Figure 6
Figure 6
Differential expressions of genes modulating the mechanism of resistance to A. alternata in naturally infected mango fruits. (A) Effect of HWB on alternaria black spot (ABS) symptom development on mango cvs. Palmer, Kent, Tommy Atkins, Keitt, Lily and Shelly. (B) ABS symptom development on naturally infected fruits cv. Keitt following HWB treatment. (C) qRT-PCR differential expression profiling of genes Syn121, glutardoxin, IT1K2 and AOS of cv. Shelly. Fruit peel tissues were sampled at four different time points after HWB treatment. RNA was extracted and served as a template for cDNA followed by qRT-PCR analysis of the genes of interest. Proportional increases in relative expression values were normalized against the samples of untreated mango fruits at 0 h. Expression data are means of two replicates. ABS-covered area was evaluated after 4 weeks of storage at 12°C. Average values followed by different letters differ significantly at P <0.05 according to the Tukey-Kramer HSD test.
Figure 7
Figure 7
Effects of HWB treatment on the expression of flavonoid biosynthesis-related genes and the occurrence of red lenticel discoloration on mango fruit cv. Shelly. (A) qRT-PCR profile of differentially expressed genes Ugft3, PAL, CFIL and CHSï, which are related to the flavonoid biosynthesis process, naringenin-chalcone synthase activity, and the phenylpropanoid biosynthesis pathway. (B) level of lenticel discoloration of HWB-treated and control fruits, and (C) lenticel discoloration symptoms on mango fruits, cv. Shelly following HWB treatment. qRT-PCR values were normalized to the values obtained in samples from untreated mango fruits at 0 h. Expression data are means of two replicates. Lenticel discoloration was evaluated following 2 weeks of storage at 12°C [9]. Average values followed by different letters differ significantly at P <0.05 according to the Tukey-Kramer HSD test.
Figure 8
Figure 8
Shelly. Effect of HWB on differential expression of chlorophyll and anthocyanin accumulation-related genes and color development in mango cv. Shelly. (A, B) qRT-PCR gene-expression profiles of genes related to (A) chlorophyll accumulation (Thl1ch, LHCIIb, Oxepch and PIRC) and (B) anthocyanin synthesis (85A2 and Anthocyanin5). The expression profile comprises data taken from samples of mango tissues sampled from cv. Shelly at four different time points after HWB treatment. (C) Changes in color index after 16 days of storage at 12°C followed by 8 days at 20°C. Vertical bars indicate SD of five replicates. qRT-PCR values were normalized to the values obtained with untreated mango fruit samples at 0 h. Expression data are the means of two replicates.
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References

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