Studies On Transcriptome Pattern Of Bagging-induced Fruit Coloration Of Red Chinese Sand Pear And Analysis Of Pear GST Gene Family

Coloration of red Chinese sand pear is mainly due to anthocyanin accumulation in peel. Many studies have been performed on the physiological and molecular basis of red Chinese sand pear. However, molecular mechanism of bagging-induced coloration remains unknown. In this study, young fruit of red Chinese sand pear ’Meirensu’ were bagged with light-proof bags until mature time. Fruit were bag-removed10days before harvest The fruit were sampled at OH (hour),3H,6H,24H,72H,144H and240H after bag-removal, bagging fruit at the same sampling time were picked as a control (HC). Samples of OH,6H,6HC (counterpart (bagging fruit) of bag-removed sample at6hours after bag-removal),24H,24HC,144H and144HC were chosen to perform transcriptomic analysis. The main results are as follows:1) Concentration of anthocyanin, carotenoid and chlorophyll were at very tow level in bagging fruit. After bag-removal, anthocyanin rapidly accumulated from72h to240h, while concentration of carotenoid and chlorophyll in peel only increased slightly. Bagging measures increased both concentration and proportion of anthocyanin in peel to improve the pear coloratioa2) In total,94.20Gb data and469,327,557reads were generated from21transcriptome sequencing libraries. After quality filtering, about70%reads could be mapped to reference genome. Reads were assembled into transcripts and compared with-reference-CDS,1,198new transcripts were predicted as new genes. All of the known and new predicted genes were annotated in five protein databases, and a total of40,935genes were functionally annotated.3) There were8,544genes found to be differentially expressed in the coloring process. Genes related light signaling pathway, plant hormone and sugar biosynthesis and signaling were significantly enriched, suggested that these genes may highly correlated with the responsive process of coloring. Q-PCR results of eight randomly selected differentially expressed genes were consistent with RNA-Seq, suggesting that results of RNA-Seq were highly accurate.4) Most of the structural genes in anthocyanin biosynthetic pathway were up-regulated after bag-removaL Among all of the DEGs,573TF encoding genes were found, from which66genes were related to anthocyanin-compounds biosynthesis process based on GO classification. Genes encoding photoreceptors and downstream elements showed irregular change at the expression level, indicating that their light-responsive events mainly occurred at the protein level. Most of the genes in ABA, JA, SAand ETH btosynthetic processes were up-regulated, genes in AUX and GA bbsynthetic pathways were down-regulated, while change of genes in sucrose bfosynthetic pathway were no regularity, suggesting that plant hormones and sugar had different rotes in fruit’s light-responsive process.Based on bioinformatic methods, pear genome database and transcriptome data, pear GST genes were identified in this study. Seventy eight GST genes were classified into seven subfamilies according to their phylogenetic relationship. Compared with Arabidopsis, gene number in U, L, DHAR and THCQD subfamilies of pear were found to be amplified. Ten conserved motifs were found in these GSTs, and most of them belonged to part of GSTN and GSTC, which were representative domain atN and C terminal of GST proteins, respectively. Obviously tissue-specfic and diverse expression pattern of GSTs were present in transcriptome data,19GSTs were found to be differentially expressed. GO classification showed that these genes took part in various processes and played important rotes in plant growth and developmentPpMYB12aad-EpGSTF12.were analyzed at sequence and expression levels, and they had98%and100%similarity with reference sequence. Many light, hormone and temperature-responsive motifs existed in their promoters, indicating that they could take part in many environmental and physiological responsive processes. PpMYB12was rapidly up-regulated after bag-removal, while PpGSTFH kept a high expression level since72h after bag-removaL Based on their functional annotation and light-responsive expression patterns, we speculated that PpMYB12and PpGSTF12might be important genes in anthocyanin biosynthesis and transporting pathway of pear.