Comparative transcriptome analysis reveals defense responses against soft rot in Chinese cabbage

Mengyang Liu,Yin Lu,Aixia Gu,Shuxing Shen,Yanhua Wang,Shan Wang,Xueping Chen,Fang Wu,Jianjun Zhao

doi:10.1038/s41438-019-0149-z

Mengyang Liu, Yin Lu + Show 7 more

Open Access

https://doi.org/10.1038/s41438-019-0149-z

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Journal: Horticulture Research	Publication Date: Jun 1, 2019
Citations: 33	License type: open-access

Affiliation: Hebei Agricultural University

Abstract

Pectobacterium carotovorum ssp. carotovorum (Pcc) is a necrotrophic bacterial species that causes soft rot disease in Chinese cabbage. In this study, plants harboring the resistant mutant sr gene, which confers resistance against Pcc, were screened from an 800 M2 population mutated by ethyl methane sulfonate (EMS) and scored in vitro and in vivo for lesion size. The transcript profiles showed ~512 differentially expressed genes (DEGs) between sr and WT plants occurring between 6 and 12 h postinoculation (hpi), which corresponded to the important defense regulation period (resistance) to Pcc in Chinese cabbage. The downstream defense genes (CPK, CML, RBOH MPK3, and MPK4) of pathogen pattern-triggered immunity (PTI) were strongly activated during infection at 12 hpi in resistant mutant sr; PTI appears to be central to plant defense against Pcc via recognition by three putative pattern recognition receptors (PRRs; BrLYM1-BrCERK1, BrBKK1/SERK4-PEPR1, BrWAKs). Pcc triggered the upregulation of the jasmonic acid (JA) and ethylene (ET) biosynthesis genes in mutant sr, but auxins and other hormones may have affected some negative signals. Endogenous hormones (auxins, JAs, and SA), as well as exogenous auxins (MEJA and BTH), were also verified as functioning in the immune system. Concurrently, the expression of glucosinolate and lignin biosynthesis genes was increased at 12 hpi in resistant mutant sr, and the accumulation of glucosinolate and lignin also indicated that these genes have a functional defensive role against Pcc. Our study provides valuable information and elucidates the resistance mechanism of Chinese cabbage against Pcc infection.

Highlights

Chinese cabbage (Brassica rapa ssp. pekinensis) originated in central China and is the most widely grown, important vegetable crop in Asia
The disease severity of WT plants inoculated with Pectobacterium carotovorum ssp. carotovorum (Pcc) was scored as 9 by both inoculation methods, and all were susceptible to Pcc (Fig. 2a)
Because of low humidity and the speed of disease development, plants could be scored in vivo at 48 hpi[34] and in vitro at 24 hpi[28], which made the disease severity accurate and met the requirements of harvesting samples for RNA-Seq analysis

Summary

Introduction

Chinese cabbage (Brassica rapa ssp. pekinensis) originated in central China and is the most widely grown, important vegetable crop in Asia. Soft rot disease caused by the pathogen Pectobacterium carotovorum ssp. Carotovorum (Pcc), known as Erwinia carotovora ssp. Carotovora (Ecc), can result in severe losses and is one of the three most economically important diseases of Chinese cabbage. Pcc employs the Type II secretion system (T2SS), which is the main way that. Liu et al Horticulture Research (2019)6:68 proteins are delivered to host cells and cause soft rot disease[5,6]. The type III secretion system (T3SS) has significant roles by contributing to virulence in hemibiotrophic phytopathogenic bacteria for secreting effectors and transporting virulence factors, but few factors are required for Pcc to attack the host plant. The pathogenicity of Pcc does not rely on T3SS to infect host plants[9]

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