Comparative Transcriptome Analysis of Different Actinidia arguta Fruit Parts Reveals Difference of Light Response during Fruit Coloration

Abstract

Kiwifruit coloration is an important agronomic trait used to determine fruit quality, and light plays a vital role in the coloration process. The effect of light on fruit coloration has been studied in many species, but differences in the photoresponse of different fruit parts during fruit coloration is unclear in kiwifruit (Actinidia arguta). In this study, peel and core with bagging and non-bagging treatment at two stages were selected to perform high throughput RNA sequencing. A total of 100,417 unigenes (25,186 unigenes with length beyond 1000 bp) were obtained, of which 37,519 unigenes were annotated in functional databases. GO and KEGG enrichment results showed that 'plant hormone signal transduction' and 'carbon metabolism' were the key pathways in peel and core coloration, respectively. A total of 27 MYB-related TFs (transcription factors) were differentially expressed in peel and core. An R2R3-MYB typed TF, AaMYB308like, possibly served as a candidate objective, which played a vital role in light-inducible fruit coloration based on bioinformatics analysis. Transient overexpression of AaMYB308like suggested overexpression of AaMYB308like elevated transcription level of NtCHI in Nicotiana tabacum leaves. Integration of all these results imply that AaMYB308like might be served as a light-responsive transcription factor to regulate anthocyanin biosynthesis in A. arguta. Moreover, our study provided important insights into photoreponse mechanisms in A. arguta coloration.

Keywords: AaMYB308like; Actinidia arguta; coloration; photoresponse; transcriptome.

Figure 1

Sample treatment and preparation for RNA-seq. (A) Fruits were bagged using two-layer light-impermeable paper bags at one month after full bloom. (B) Peel and core were collected from bagged and unbagged fruit making a total of eight typed samples used for RNA-seq. (C) The anthocyanin content of these eight typed samples. Note: S1—fruit stage at 70 days after full bloom, S2—fruit stage at 110 days after full bloom, TP70—peel from bagged fruit at S1, TX70—core from bagged fruit at S1, TP110—peel from bagged fruit at S2, TX110—core from bagged fruit at S2, WP70—peel from unbagged fruit at S1, WX70—core from unbagged fruit at S1, WP110—peel from unbagged fruit at S2, WX110—core from unbagged fruit at S2. Data were analyzed with Student’s t-test (** p < 0.01).

Figure 2

GO classification of DEGs from WP110 vs. TP110 and WX110 vs. TX110. (A) GO classification of DEG unigenes from WP110 vs. TP110. (B) GO classification of DEG unigenes from WX110 vs. TX110. The x-axis in (A,B) represents GO level-two terms belonging to three GO categories including biological process, cellular component, and molecular function. The y-axis in (A,B) represents the percentage and number of unigenes.

Figure 3

The possible MYB-related genes involved in light-inducible fruit coloration. (A) Venn diagram of MYB-typed DEGs between WP110 vs. TP110 and WX110 vs. TX110. (B) The transcription level of 27 MYB-typed DEGs. (C) The analysis of functional protein association networks in Arabidopsis for MYB4 as the closest ortholog available of c72412.graph_c1. (D) Phylogeny analysis of c72412.graph c1 and its top 20 homologous genes in NCBI blast. The way of phylogenetic tree construction is Construct/Test Neighbor-Joining Tree in MEGA 6.0 software (Version 6.0, Mega Limited, Auckland, New Zealand). The orange shadow mutates the transcript c72412.graph c1. The setting bar for genetic distance is 0.02.

Figure 4

Transient overexpression of AaMYB308like in Nicotiana tabacum leaves. (A) Phenotype of Nicotiana tabacum leaves five days after AaMYB308like overexpression. Scale bars: 1 cm. (B) Relative expression level of structural genes involved in anthocyanin biosynthetic pathway. OE represents overexpression of AaMYB308like. Data were analyzed with Student’s t-test (*** p < 0.001).