Three Main Genes in the MAPK Cascade Involved in the Chinese Jujube-Phytoplasma Interaction

Zhiguo Liu,Lili Wang,Chaoling Xue,Chunfang Feng,Mengjun Liu,Liman Zhang,Lixin Wang,Jin Zhao,Zhe Yu,Zhihui Zhao

doi:10.3390/f10050392

Abstract

Chinese jujube (Ziziphus jujuba Mill.) is an important economic forest species and multipurpose fruit tree in the family of Rhamnaceae. Phytoplasmas are significant prokaryotic pathogens, associated with more than 1000 plant diseases. Jujube witches’ broom disease (JWB) is a typical phytoplasma disease, caused by ‘Candidatus Phytoplasma ziziphi’. Mitogen-activated protein kinase (MAPK) cascades are highly universal signal transduction modules and play crucial roles in regulating innate immune responses in plants. Thus, in the current study, systematical expression profiles of 10 ZjMPK and 4 ZjMPKK genes were conducted in plantlets with JWB disease, plantlets recovered from JWB disease, the tissues showing different disease symptoms, and resistant/susceptible cultivars infected by JWB phytoplasma. We found that most ZjMPK and ZjMKK genes exhibited significant up- or down-regulation expression under phytoplasma infection, but the top three differentially expressed genes (DEGs) were ZjMPK2, ZjMKK2 and ZjMKK4, which showed the biggest times of gene’s significant difference expression in all materials. Based on STRING database analysis, ZjMKK2 and ZjMPK2 were involved in the same plant-pathogen interaction pathway, and Yeast two-hybrid screening showed that ZjMKK2 could interact with ZjMPK2. Finally, we deduced a pathway of jujube MAPK cascades which response to ‘Candidatus Phytoplasma ziziphi’ infection. Our study presents the first gene-family-wide investigation on the systematical expression analysis of MAPK and MAPKK genes in Chinese jujube under phytoplasma infection. These results provide valuable information for the further research on the signaling pathway of phytoplasma infection in Chinese jujube.

Highlights

Plant pathogenic phytoplasmas, members of the class Mollicutes, are non-helical, cell wall-less bacterial organisms that are confined in the phloem sieve elements of infected plants [1,2]
4 ZjMKK genes in healthy, Jujube witches’ broom disease (JWB)-diseased and recovered plantlets by quantitative real-time PCR (qRT-PCR) and try to find out the potential genes responding to phytoplasma infection
Protein-protein interaction analysis showed that ZjMPK2 and ZjMKK2 were involved in the same plant-pathogen interaction pathway (Figure S3), and our present study showed that ZjMKK2 could interact with ZjMPK2 by yeast two hybrid analysis (Figure S4)

Summary

Introduction

Members of the class Mollicutes, are non-helical, cell wall-less bacterial organisms that are confined in the phloem sieve elements of infected plants [1,2]. TENGU) have been shown to modulate plant development, including indeterminate leaf-like flower development, morphology alternation and sterility in Arabidopsis plants [5,6,7]. These results indicate that phytoplasma effectors play an important role in phytoplasma pathogenesis. Chinese jujube (Ziziphus jujuba Mill.), known as Chinese date, is an important economic forest species and multipurpose fruit tree in the family of Rhamnaceae. It has been cultivated in China for up to 7000 years and has been introduced to 47 countries throughout Americas, southern and eastern

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Conclusion