Bioinformatics and Expression Analysis of the WRKY Gene Family in Apple

【Objective】In this study, 132 putative WRKY proteins in the apple(Malus domestica Borkh.) genome were identified, so as to provide a basis for studying the theoretical roles of WRKY genes in the regulation of plant stress responses, growth and development, and to provide valuable information for WRKY genes cloning in apple.【Method】WRKY DNA-binding domain(PF03106) downloaded from Pfam protein families database was employed to identify WRKY genes from apple genome using HMMER 3.0. The obtained amino acid sequences were analyzed with the bioinformatics softwares, including DNAMAN 5.0, Weblogo 3, MEGA 5.1, Map Inspect and MEME. RT-PCR was used to detect WRKY genes expression in different tissues of apple. 【Result】 Totally 132 apple WRKY genes were found in apple genome. The result of group identification and phylogenetic analysis revealed that apple WRKY genes were classified into Group I, Group II and Group III. Twenty-four Md WRKY proteins with two WRKY domains(group I-N and group I-C) containing CX4CX22-23 HXH zinc-finger motif belonged to Group I. Seventy-nine Group II Md WRKY proteins had a single WRKY domain including CX4–5CX23HXH zinc-finger motif and could be further divided into five subgroups(Group II-a: 8 members, Group II-b: 12 members, Group II-c: 31 members, Group II-d: 14 members, and Group II-e: 14 members, respectively), whereas 29 Group III Md WRKY proteins contained a single WRKY domain with CX7CX23–24HXC zinc-finger motif. The results of domain analysis indicated that the WRKY regions contained a highly conserved heptapeptide stretch WRKYGQK at its N-terminus followed by a zinc-finger motif. Chromosome mapping analysis showed that apple WRKY genes were distributed with different densities on 17 chromosomes. The largest number of apple WRKY genes were found on chromosomes 1 and 9(thirteen genes), followed by chromosome 12(twelve genes). Only 4 genes located on chromosomes 2, 5 and 14. The results of gene structure analysis revealed that most of the WRKY gene contained 2-5 exons and WRKY gene structure were highly conserved in apple. Conserved motif analysis showed that the conserved motifs 1-6, which specify the WRKY domain, were observed in all apple WRKY proteins, motif 8 and motifs 7 and 9 as the unknown domain were observed in Group II-a and II-b and Group III, respectively. Two WRKY domains were assigned to Group I. RT-PCR results indicated that 12 Md WRKY genes were expressed in roots, stems, leaves, flowers and fruits at various expression levels.【Conclusion】These results suggested that Md WRKY gene family was highly and structurally conserved, and may be involved into the regulation of growth and development processes in apple.