Lilium regale Wilson WRKY2 Regulates Chitinase Gene Expression During the Response to the Root Rot Pathogen Fusarium oxysporum.

Shan Li,Jun Hai,Jie Deng,Diqiu Liu,Linlin Su,Tingting Liang,Zie Wang

doi:10.3389/fpls.2021.741463

Shan Li, Jun Hai + Show 5 more

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https://doi.org/10.3389/fpls.2021.741463

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Abstract

Root rot, mainly caused by Fusarium oxysporum, is the most destructive disease affecting lily (Lilium spp.) production. The WRKY transcription factors (TFs) have important roles during plant immune responses. To clarify the effects of WRKY TFs on plant defense responses to pathogens, a WRKY gene (LrWRKY2) was isolated from Lilium regale Wilson, which is a wild lily species highly resistant to F. oxysporum. The expression of LrWRKY2, which encodes a nuclear protein, is induced by various hormones (methyl jasmonate, ethephon, salicylic acid, and hydrogen peroxide) and by F. oxysporum infection. In this study, LrWRKY2-overexpressing transgenic tobacco plants were more resistant to F. oxysporum than the wild-type plants. Moreover, the expression levels of jasmonic acid biosynthetic pathway-related genes (NtAOC, NtAOS, NtKAT, NtPACX, NtJMT, NtOPR, and NtLOX), pathogenesis-related genes (NtCHI, NtGlu2, and NtPR-1), and antioxidant stress-related superoxide dismutase genes (NtSOD, NtCu-ZnSOD, and MnSOD) were significantly up-regulated in LrWRKY2 transgenic tobacco lines. Additionally, the transient expression of a hairpin RNA targeting LrWRKY2 increased the susceptibility of L. regale scales to F. oxysporum. Furthermore, an F. oxysporum resistance gene (LrCHI2) encoding a chitinase was isolated from L. regale. An electrophoretic mobility shift assay demonstrated that LrWRKY2 can bind to the LrCHI2 promoter containing the W-box element. Yeast one-hybrid assay results suggested that LrWRKY2 can activate LrCHI2 transcription. An examination of transgenic tobacco transformed with LrWRKY2 and the LrCHI2 promoter revealed that LrWRKY2 activates the LrCHI2 promoter. Therefore, in L. regale, LrWRKY2 is an important positive regulator that contributes to plant defense responses to F. oxysporum by modulating LrCHI2 expression.

Highlights

Plants have evolved a series of responsive and adaptive mechanisms to cope with various stresses
Researchers previously identified 35 WRKY genes by sequencing the wild L. regale transcriptome during an F. oxysporum infection; they revealed that LrWRKY2 expression is induced by F. oxysporum and is substantially affected by methyl jasmonate (MeJA), salicylic acid (SA), ETH, and H2O2 treatments (Li et al, 2021a)
Transgenic tobacco lines overexpressing LrWRKY2 are highly resistant to F. oxysporum, which may be related to the significantly up-regulated expression of many defense-related genes, including jasmonic acid (JA) biosynthetic pathway-related genes, PR genes, and superoxide dismutase (SOD) genes

Summary

Introduction

Plants have evolved a series of responsive and adaptive mechanisms to cope with various stresses. The WRKY transcription factors (TFs), which represent one of the largest families of transcriptional regulators in plants, are mainly involved in regulating the plant immune system during responses to stress (Wang P. et al, 2018). LrWRKY2 Regulates Lrchi Exprssion or two conserved domains comprising approximately 60 amino acids (Yan et al, 2019a). On the basis of the number of WRKY domains and the structure of the zinc-finger motif, WRKY TFs have been classified into three main groups (I, II, and III) (Dong et al, 2020). The Group II WRKY TFs have been further divided into Subgroups IIa, IIb, IIc, IId, and IIe according to their primary amino acid sequences (Huang et al, 2015)

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