De Novo Assembly of a Genome-Wide Transcriptome of Paw-Paw (Asimina triloba; Annonaceae) and Functional Annotations of Fruit Development

Paw-paw (Asimina triloba Dunal; Annonaceae) is the only species in the genus Asimina found in eastern North America, and it bears the largest indigenous fruit to the continent. Despite its economical and ecological importance, the lack of transcriptomic and genomic data limits the genomic and genetic investigation of this important fruit tree. The transcriptome from early fruit developmental stage (14 days after pollination) was sequenced in order to generate expression datasets of three genotypes (Davis, NC1 and PG). A total of 45 million reads (Illumina 150 bp paired-end reads) were obtained from the fruits of the three genotypes. High quality reads were assembled de novo into 406,979 unique transcripts (UTs). An average of 49,091 UTs were assigned to 1,177 Gene Ontology (GO) terms. Using the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database, we mapped an average of 480 GO terms onto 109 pathways. Ethylene responsive pathway-related candidate genes were expressed significantly higher (p < 0.05) than randomly selected genes. This study produced the first fruit trnascriptome sequence of Asimina, and it identifed several candidate genes in the ethylene responsive pathway for the fruit development.