PhWRKY30 activates salicylic acid biosynthesis to positively regulate antiviral defense response in petunia

Authors: WANG, MEILING - Northwest Agricultural & Forestry University; YUAN, YANPING - Northwest Agricultural & Forestry University; ZHAO, YIKE - Northwest Agricultural & Forestry University; HU, ZHUO - Northwest Agricultural & Forestry University; ZHANG, SHASHA - Northwest Agricultural & Forestry University; Jiang, Cai Zhong; LUO, JIANRANG - Northwest Agricultural & Forestry University; ZHANG, YANLONG - Northwest Agricultural & Forestry University; SUN, DAOYANG - Northwest Agricultural & Forestry University

Submitted to: Horticulture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: To adapt to natural environments with a diverse spectrum of pathogens, plants have evolved immune mechanisms that elicit numerous downstream responses, including the generation of reactive oxygen species (ROS), influx of calcium ions, activation of mitogen-activated protein kinases, endogenous hormone synthesis, and transcriptional reprogramming. Salicylic acid (SA) is a key hormone signal to activate the immune mechanisms for resisting various types of pathogens, including viruses. Many studies have indicated that exogenous SA application enhanced the resistance of plants to some viruses, such as Cucumber mosaic virus (CMV), Cauliflower mosaic virus, Potato virus X, Tobacco mosaic virus (TMV), Tomato yellow leaf curl virus, Mungbean yellow mosaic virus, and Sorghum mosaic virus. Petunia (Petunia hybrida) is globally recognized as the most preferred annual bedding plant due to its abundant, sizable, and vibrant flowers. Nevertheless, petunia plants are highly threatened by a diversity of viruses, causing substantial damage to ornamental quality and seed yield. However, the regulatory mechanism of virus resistance in petunia is largely unclear. In this study, we revealed that a regulatory protein (a WRKY transcription factor, PhWRKY30) played a critical role in the regulation of antiviral defense against TRV and TMV infections through modulation of SA pathway. The findings from this study will be helpful to control virus disease through molecular genetic engineering in petunia.

Technical Abstract: Petunia (Petunia hybrida) plants are highly threatened by a diversity of viruses, causing substantial damage to ornamental quality and seed yield. However, the regulatory mechanism of virus resistance in petunia is largely unclear. Here, we revealed that a member of petunia WRKY transcription factors, PhWRKY30, was dramatically up-regulated following Tobacco rattle virus (TRV) infection. Down-regulation of PhWRKY30 through TRV-based virus-induced gene silencing increased green fluorescent protein (GFP)-marked TRV RNA accumulation and exacerbated the symptomatic severity. In comparison to wild-type (WT) plants, PhWRKY30-RNAi transgenic petunia plants exhibited a compromised resistance to TRV infection, whereas an enhanced resistance was observed in PhWRKY30-overexpressing (OE) transgenic plants. PhWRKY30 affected salicylic acid (SA) production and expression of arogenate dehydratase 1 (PhADT1), phenylalanine ammonia-lyase 1 (PhPAL1), PhPAL2b, non-expressor of pathogenesis-related proteins 1 (PhNPR1), and PhPR1 in SA biosynthesis and signaling pathway. SA treatment restored the reduced TRV resistance to WT levels in PhWRKY30-RNAi plants, and application of SA biosynthesis inhibitor 2-aminoindan-2-phosphonic acid inhibited promoted resistance in PhWRKY30-OE plants. The protein-DNA binding assays showed that PhWRKY30 specifically transactivated the promoter of PhPAL2b. RNAi silencing and overexpression of PhPAL2b led to decreased and increased TRV resistance, respectively. The transcription of a few reactive oxygen species- and RNA silencing-associated genes was changed in PhWRKY30 and PhPAL2b transgenic lines. PhWRKY30 and PhPAL2b were further characterized to be involved in the resistance to Tobacco mosaic virus (TMV) invasion. Our findings demonstrate that PhWRKY30 positively regulates antiviral defense against TRV and TMV infections by modulating SA content.