The Identification,Expression Analysis Of WRKY Gene Family In Apple And Function Verification Of MdWRKY118 Gene

WRKY proteins,a family of transcription factor in higher plants,have functions in many biological processes,such as plant growth and development,response to biotic and abiotic stresses.In this study,genome-wide identification of WRKY family genes was performed in apple,and analyzed their evolution relationship.We analyzed and compared their expression profiles under hormone treatments and fungal pathogen infection using qRT-PCR.In addition,we made further investigation of MdWRKY118 by transgenic method.The results are as follows:1.In this study,we identified 119 candidate WRKY genes in apple genome.According to the structural features of these proteins,the identified WRKY transcription factors were classified into three main groups(GroupI-?).These WRKY genes were anchored on 17 chromosomes in apple with uneven distribution.Most of the MdWRKY genes contain one to five introns.And the exon-intron structures and motif compositions are similar in the same group or subgroup.Meanwhile,we found 20 tandem duplication events and 85 paired collinearity relationships in all the MdWRKY genes.2.The transcript abundance of sixty-three WRKY genes transcript abundance was affected by Alternaria alternate apple pathotype.We found the expression of 31 MdWRKY genes which induced by pathogen was also changed significantly in different time after treating by one or more hormones.The result suggested that MdWRKY genes involved in apple defense response to fungal pathogen infection and play roles in SA,JA or ETH signal pathways.3.In this study,we cloned MdWRKY118 gene from 'Golden Delicious',and constructed plant binary-vector pYH4215-MdWRKY118.The gene was transformed into Arabidopsis ecotype Columbia plants(Col-0).Homozygous T3 seeds of transgenic Arabidopsis and wild type(WT)lines were selected for further analysis.The over-expressing lines and WT Arabidopsis showed no difference in germination rate on 1/2 MS media.Under salt treatment,the over-expressing lines showed a lower germination rate compared to WT.In addition,the seedlings of WT growth better than MdWRKY118-overexpressing lines.Under drought treatment,the over-expressing lines showed a higher germination rate compared to WT.But the seedlings of WT growth better than MdWKY118-overexpressing lines.The MdWRKY118-overexpressing lines show a hypersensitive phenotype to salt and drought stress compared with WT plants;the MdWKY118-overexpressing lines were wilted after salt and drought treatment for 10 d and 15 d,whereas WT plants remained healthier than the overexperssing lines.The results indicated that MdWRKY118 may act as a negative regulator involved in the Arabidopsis response to salt and drought stress.4.We investigated the function of MdWRKY118 gene during infection by Pseudomonas syringae pv.tomato DC3000(Pst DC3000).In the work,compared to WT plants,MdWRKY118-overexpressing lines was no significant difference to Pst DC3000 infection.