Analysis of WRKY transcription factors and characterization of two Botrytis cinerea-responsive LrWRKY genes from Lilium regale

A major constraint in producing lilies is gray mold caused by Botrytis elliptica and B. cinerea. WRKY transcription factors play important roles in plant immune responses. However, limited information is available about the WRKY gene family in lily plants. In this study, 23 LrWRKY genes with complete WRKY domains were identified from the Botrytis-resistant species Lilium regale. The putative WRKY genes were divided into seven subgroups (Group I, IIa-e, and III) according to their structural features. Sequence alignment revealed that LrWRKY proteins have a highly conserved WRKYGQK domain and a variant, the WRKYGKK domain, and these proteins generally contained similar motif compositions throughout the same subgroup. Functional annotation predicted they might be involved in biological processes related to abiotic and biotic stresses. A qRT-PCR analysis confirmed that expression of six LrWRKY genes in L. regale or the susceptible Asian hybrid 'Yale' was induced by B. cinerea infection. Among these genes, LrWRKY4, LrWRKY8 and LrWRKY10 were expressed at a higher level in L. regale than 'Yale', while the expression of LrWRKY6 and LrWRKY12 was lower in L. regale. Furthermore, LrWRKY4 and LrWRKY12 genes, which also respond to salicylic acid (SA) and methyl jasmonate (MeJA) treatments, were isolated from L. regale. Subcellular localization analysis determined that they were targeted to the nucleus. Constitutive expression of LrWRKY4 and LrWRKY12 in Arabidopsis resulted in plants that were more resistant to B. cinerea than wild-type plants. This resistance was coupled with the transcriptional changes of SA and JA-responsive genes. Overall, our study provides valuable information about the structural and functional characterization of LrWRKY genes that will not only deepen our understanding of the molecular mechanisms underlying the defense of lily against B. cinerea but also offer potential targets for cultivar improvement via biotechnology.