Genome-wide identification, characterisation and functional evaluation of WRKY genes in the sweet potato wild ancestor Ipomoea trifida (H.B.K.) G. Don. under abiotic stresses

BACKGROUND: WRKY DNA-binding protein (WRKY) is a large gene family involved in plant responses and adaptation to salt, drought, cold and heat stresses. Sweet potato from the genus Ipomoea is a staple food crop, but the WRKY genes in Ipomoea species remain unknown to date. Hence, we carried out a genome-wide analysis of WRKYs in Ipomoea trifida (H.B.K.) G. Don., the wild ancestor of sweet potato. RESULTS: A total of 83 WRKY genes encoding 96 proteins were identified in I. trifida, and their gene distribution, duplication, structure, phylogeny and expression patterns were studied. ItfWRKYs were distributed on 15 chromosomes of I. trifida. Gene duplication analysis showed that segmental duplication played an important role in the WRKY gene family expansion in I. trifida. Gene structure analysis showed that the intron-exon model of the ItfWRKY gene was highly conserved. Meanwhile, the ItfWRKYs were divided into five groups (I, IIa + IIb, IIc, IId + IIe and III) on the basis of the phylogenetic analysis on I. trifida and Arabidopsis thaliana WRKY proteins. In addition, gene expression profiles confirmed by quantitative polymerase chain reaction showed that ItfWRKYs were highly up-regulated or down-regulated under salt, drought, cold and heat stress conditions, implying that these genes play important roles in response and adaptation to abiotic stresses. CONCLUSIONS: In summary, genome-wide identification, gene structure, phylogeny and expression analysis of WRKY gene in I. trifida provide basic information for further functional studies of ItfWRKYs and for the molecular breeding of sweet potato.