CaWRKY30 Positively Regulates Pepper Immunity by Targeting CaWRKY40 against Ralstonia solanacearum Inoculation through Modulating Defense-Related Genes.

Ansar Hussain,Ali Tan Kee Zuan,Ijaz Rasool Noorka,Zhiqin Liu,Ahmed M El-Shehawi,Bandar S Aljuaid,Mohammed Albaqami,Shahid Farooq,Shahzadi Mahpara,Muhammad Ifnan Khan,Mohamed A A Ahmed

doi:10.3390/ijms222112091

Abstract

The WRKY transcription factors (TFs) network is composed of WRKY TFs’ subset, which performs a critical role in immunity regulation of plants. However, functions of WRKY TFs’ network remain unclear, particularly in non-model plants such as pepper (Capsicum annuum L.). This study functionally characterized CaWRKY30—a member of group III Pepper WRKY protein—for immunity of pepper against Ralstonia solanacearum infection. The CaWRKY30 was detected in nucleus, and its transcriptional expression levels were significantly upregulated by R. solanacearum inoculation (RSI), and foliar application ethylene (ET), abscisic acid (ABA), and salicylic acid (SA). Virus induced gene silencing (VIGS) of CaWRKY30 amplified pepper’s vulnerability to RSI. Additionally, the silencing of CaWRKY30 by VIGS compromised HR-like cell death triggered by RSI and downregulated defense-associated marker genes, like CaPR1, CaNPR1, CaDEF1, CaABR1, CaHIR1, and CaWRKY40. Conversely, transient over-expression of CaWRKY30 in pepper leaves instigated HR-like cell death and upregulated defense-related maker genes. Furthermore, transient over-expression of CaWRKY30 upregulated transcriptional levels of CaWRKY6, CaWRKY22, CaWRKY27, and CaWRKY40. On the other hand, transient over-expression of CaWRKY6, CaWRKY22, CaWRKY27, and CaWRKY40 upregulated transcriptional expression levels of CaWRKY30. The results recommend that newly characterized CaWRKY30 positively regulates pepper’s immunity against Ralstonia attack, which is governed by synergistically mediated signaling by phytohormones like ET, ABA, and SA, and transcriptionally assimilating into WRKY TFs networks, consisting of CaWRKY6, CaWRKY22, CaWRKY27, and CaWRKY40. Collectively, our data will facilitate to explicate the underlying mechanism of crosstalk between pepper’s immunity and response to RSI.

Highlights

Plants frequently get exposed to various biotic and abiotic stresses during their life span due to their immobile nature [1,2]
The results indicated that rel transcriptional expression levels of CaWRKY30 were enhanced from 0 h to 48 hpt with μM ET as compared to mock
2O2 accumulation in pepper leaves manifested by darker cell death and H2 O2 accumulation in pepper leaves manifested by darker trypan blue trypan blue staining andDAB

Summary

Introduction

Plants frequently get exposed to various biotic and abiotic stresses during their life span due to their immobile nature [1,2]. Plants have developed several defense mechanisms in response to repeated selection pressure from major ecological and environmental constraints. Different transcriptional factors (TFs) interconnect to develop sophisticated transcriptional networks for regulating these classic defense mechanisms at a transcriptional level [3,4]. Defense reactions to various stresses are properly synchronized and controlled as they are critical for plants in the form of energy expenditure and development [5]. The defense mechanisms might vary in different plant species because of varied environmental circumstances affecting their acclimation [6–8]. Defense system employed by model plants cannot be fully implied to non-model plants. Defense systems of plants have been a prime focus during past decades; these studies were mostly focused on model plants, i.e., Arabidopsis thaliana and rice (Oryza sativa L.). Functional synchronization of these transcriptional complexes to regulate plants’ response to various stresses has been poorly investigated, mainly in non-model plants

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Conclusion