Full-Length Transcriptome-Wide Characteristic and Functional Identification of WRKY Family in Malus sieversii during the Valsa Canker Disease Response

WRKY transcription factors are one of the largest families in plants, playing important roles in regulating plant immunity. Malus sievesii has abundant genetic diversity and can offer various and high-quality gene resources. In this study, 112 putative MsWRKY proteins were identified from a full-length transcriptome of M. sieversii during the Valsa canker disease (caused by Valsa mali). The MsWRKY proteins were phylogenetically divided into three groups (I–III). Motif compositions of the MsWRKY proteins were clustered and fifteen conserved motifs were observed. Expression pattern analysis showed that thirty-four MsWRKY transcripts strongly responded to the V. mali infection, demonstrating that MsWRKY transcripts might play different roles during the response. Functional identifications were subsequently conducted with transient expressions, demonstrating that MsWRKY16, MsWRKY21, MsWRKY70, MsWRKY74 and MsWRKY85 positively regulated the resistant response. Besides, the MsWRKY21, MsWRKY70 and MsWRKY85 were dramatically induced by salicylic acid (SA), methyl-jasmonate acid (MeJA) and 1-aminocyclopropane-1-carboxylate (ACC), indicating that they play important roles in the regulatory resistance of V. mali infection. This work provides a comprehensive understanding of the WRKY family in M. sieversii and will build a foundation for future research of the potential disease resistances MsWRKY transcripts.