A Novel Pepper (Capsicum annuum L.) WRKY Gene, CaWRKY30, Is Involved in Pathogen Stress Responses

WRKY proteins are a superfamily of transcription factors involved in many plant processes including plant defense responses to biotic and abiotic stresses. We isolated a WRKY gene from pepper during the incompatible interaction between the pepper cultivar HDA149 and Meloidogyne incognita. The full-length gene, named as CaWRKY30, has a 1,533-bp cDNA sequence and contains an open reading frame of 1,095 bp, encodes a putative polypeptide of 364 amino acids with a theoretical protein size of 41.2 kDa, and contains one WRKY domain followed by a zinc-finger motif. The genomic sequence of CaWRKY30 contains three exons and two introns. Southern blot analysis confirmed that CaWRKY30 exists as a single copy in the pepper cultivar HDA149 genome. Quantitative RT-PCR showed that CaWRKY30 is up-regulated by application of various pathogens including avirulent M. incognita, Tobacco mosaic virus, Ralstonia solanacerum, and Phytophthora capsici Leonian. Furthermore, the transcripts of CaWRKY30 were rapidly induced after treatment with phytohormones salicylic acid (SA). However, the expression of CaWRKY30 was down-regulated by virulent M. incognita and phytohormones methyl jasmonic acid (MeJA). In addition, the nuclear localization of CaWRKY30 was determined when a CaMV35s::CaWRKY30-eGFP fusion construct was expressed in onion epidermal cells. These results suggested that CaWRKY30 might be involved in plant defense mechanisms against the diverse pathogen infection.