Transcriptome Sequencing of the Sweet Potato Progenitor (Ipomoea trifida (H.B.K.) G. Don.) and Discovery of Drought Resistance Genes

Ipomoea trifida (H.B.K.) G. Don. is the closest wild relative of cultivated sweet potato (I. batatas). The diploid I. trifida plays an important role in sweet potato breeding and construction of transgenic systems. It also can be used to discover functional genes, particularly stress resistance genes lost during the domestication of sweet potato. However, the transcriptome information of I. trifida is limited, compared to I. batatas data. Using high-throughput Illumina RNA-seq technology, a total of 66,329,578 paired-end 101 bp reads were cleaned and assembled de novo to produce 90,864 I. trifida transcripts. Based on sequence similarity, 69,541, 39,236, 12,509, 2,848 and 2,766 transcripts were annotated using homologous proteins from NCBI NR database, GO terms, KEGG pathways, known transcription factors and protein kinases, respectively. Great differences were found between the I. trifida. and I. batatas transcriptomes.

This is the first report of a comprehensive transcriptome for diploid I. trifida, with gene expression information for root, leaf, stem and flower tissues. The I. trifida transcriptome sequences enrich the gene resources for sweet potato molecular research and breeding. Moreover, we demonstrated that these sequences could be used to design SSR markers and for gene discovery in I. trifida. In particular, we found a potential drought resistance gene ItWRKY1 from I. trifida and validated its function using the transgenic tobacco system.