Transcriptome Sequencing of the Sweet Potato Progenitor (Ipomoea Trifida (HBK) G. Don.) and Discovery of Drought Tolerance Genes

Ipomoea trifida (H.B.K.) G. Don. is the closest wild relative of cultivated sweet potato (I. batatas). The diploid I. trifida is important for sweet potato breeding and construction of transgenic systems. It can also be used to discover functional genes, particularly stress tolerance genes which had been lost during the domestication of sweet potato. Compared to the abundant I. batatas transcriptome data, the nucleotide sequences of diploid I. trifida are rare. Using high-throughput Illumina RNA-seq technology, a total of 66,329,578 paired-end 101 bp reads were sequenced and de novo assembled to produce 90,684 I. trifida transcripts. Based on sequence similarity searches, 69,540, 39,236, 19,768, 2848 and 2766 transcripts were annotated by their homologous proteins from NCBI NR database, GO terms, KEGG pathways, known transcription factors and protein kinases, respectively. The I. trifida transcriptome has a medium heterozygous rate of 0.04 %. The difference between I. trifida and I. batatas transcriptome is out of expectation. In this study, we first reported a comprehensive transcriptome for the diploid I. trifida, which contained gene expression information in root, leaf, stem and flower tissues. The I. trifida transcript sequences enriched the gene resources for sweet potato molecular research and breeding. In addition, we demonstrated that these sequences could be used to design SSR markers and clone functional genes. Particularly, we cloned a potential drought tolerance gene ItWRKY1 from I. trifida and validated its function using Agrobacterium-mediated tobacco transformants.