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

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 unknown. 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 with 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, nonexpressor 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 bound to the promoter of PhPAL2b. RNAi silencing and overexpression of PhPAL2b led to decreased and increased TRV resistance, respectively. The transcription of a number of 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.

Acknowledgements

We are grateful to Mengchen Li for EMSA and hormone measurement. We thank Yong Jia for protein modeling analysis. We also appreciate the insightful and helpful comments from anonymous reviewers for improving this manuscript. This work was funded by National Natural Science Foundation of China (Grant nos. 32271953 and 31801895), Key Research and Development Plan Project in Shaanxi Province (grant no. 2023-YBNY-081), Basic Scientific Research Project in Northwest A&F University (grant nos Z1090323002 and Z1090322159).

Author contributions

M.W., Y.Y., and D.S. designed the experiments. M.W., Y.Y., Y.K.Z., Z.H., and S.Z. carried out the experiments. Y.Y. offered the experimental materials. M.W., Y.Y., and Y.K.Z. prepared the chemical reagents. C.J., J.L., Y.L.Z., and D.S. organized and analyzed the data. M.W. and Y.Y. wrote the manuscript. C.J. and D.S. modified the manuscript.

Data availability

All data supporting the conclusions of this study are present in the paper or Supplementary files.

Conflict of interest statement

The authors declare that they have no conflict of interest.

Supplementary Data

Supplementary data is available at Horticulture Research online.

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