Characterization of the transcriptome and EST-SSR development in Boea clarkeana, a desiccation-tolerant plant endemic to China

Background. Resurrection plants constitute a unique cadre within angiosperms. Boea clarkeana Hemsl. (Boea, Gesneriaceae) is a desiccation-tolerant dicotyledonous herb that is endemic to China. Although research on angiosperms with DT could be instructive for crops, genomic resources for B. clarkeana remain scarce. In addition, transcriptome sequencing could be an effective way to study desiccation-tolerant plants. Methods. In the present study, we used the platform Illumina HiSeq^TM 2000 and de novo assembly technology to obtain leaf transcriptomes of B. clarkeana and conducted a BLASTX alignment of the sequencing data and protein databases for sequence classification and annotation. Then, based on the sequence information obtained, we developed EST-SSR markers by means of EST-SSR mining, primer design and polymorphism identification. Results. A total of 91,449 unigenes were generated from the leaf cDNA library of B. clarkeana in this study. Based on a sequence similarity search with a known protein database, 72,087 unigenes were annotated. Among the annotated unigenes, a total of 71,170 unigenes showed significant similarity to known proteins of 463 popular model species in the Nr database, and 59,962 unigenes and 32,336 unigenes were assigned to GO classifications and COG, respectively. In addition, 44,924 unigenes were mapped in 128 KEGG pathways. Furthermore, a total of 7,610 unigenes with 8,563 microsatellites were found. Seventy-four primer pairs were selected from 436 primer pairs designed for polymorphism validation. SSRs with higher polymorphism rates were concentrated on dinucleotides, pentanucleotides and hexanucleotides. Finally, 17 pairs with highly polymorphic and stable loci were selected for polymorphism screening. There were a total of 65 alleles, with 2–6 alleles at each locus. Mainly due to the unique biological characteristics of plants, the H_E, H_O and PIC per locus were very low, ranging from 0 to 0.196, 0.082 to 0.14 and 0 to 0.155, respectively. Discussion. A substantial fraction transcriptome sequences of B. clarkeana were generated in this study, which is the first molecular-level analysis of this plant. These sequences are valuable resources for gene annotation and discovery and molecular marker development. These sequences could also provide a valuable basis for the future molecular study of B. clarkeana.