Genome-wide identification of WRKY gene family and expression analysis under abiotic stresses in Andrographis paniculata

Andrographis paniculata (A. paniculata) is a Chinese herbal medicine that clears away heat, reduces inflammation, protects the liver, and promotes choleretics. The WRKYs of A. paniculata are still not well characterized, although many WRKYs have been identified in various plant species. In the present study, 59 A. paniculata WRKY (ApWRKY) genes were identified and renamed on the basis of their respective chromosome distribution. These ApWRKYs were divided into three groups via phylogenetic analysis according to their WRKY domains and combined with WRKY of Arabidopsis. The 59 identified ApWRKY transcription factors were non-uniformity distributed on 23 chromosomes of A. paniculata. From the structural analysis of the conserved motifs, different ApWRKYs structures showed different biological functions, and the ApWRKY transcription factor had certain species-specificity in the evolutionary process. The expression patterns of the 41 ApWRKYs were examined through quantitative real-time PCR (qRT-PCR) in various tissues and under abiotic stresses (salt). The results showed that most of the ApWRKY had different reactions to salt treatment. In addition, the content of the four main secondary metabolites in A. paniculata leaves was determined under salt stress. The results show that under a low concentration of salt treatment, the synthesis of andrographolide can be improved.