Genome-wide analysis of the WRKY gene family and their positive responses to phytoplasma invasion in Chinese jujube

Abstract

Background The WRKY gene family is one of the most important families in higher plants. As transcription factors, they actively respond to biotic and abiotic stress and are also involved in plant development. Chinese jujube ( Ziziphus jujuba Mill.) is the largest type of dried fruit tree in China in terms of production, but its production is largely limited by phytoplasma infection, and the information about the role of WRKY genes under phytoplasma stress was still limited. Results We identified 54 ZjWRKYs in the jujube genome and classified them into three subgroups according to conserved WRKY domains and zinc-finger structure. 41 ZjWRKYs were distributed on 11 of 12 pseudo chromosomes in Chinese jujube. The majority of ZjWRKYs were highly expressed in the seven examined tissues, indicating that they play multiple roles in these vegetative and reproductive organs. Transcriptome data showed that most of the characterised ZjWRKYs were highly expressed at later stages of fruit development. RT-qPCR demonstrated that the expression of 23 ZjWRKYs changed following phytoplasma infection, suggesting that they are involved in signalling pathways that respond to phytoplasma stress. Then, STRING analysis and yeast two-hybrid screening proved that some ZjWRKY proteins were interacting with ZjMAPKK proteins, which were also involved in phytoplasma invasion. Moreover, their differential expressions were further confirmed in resistant and susceptible jujube varieties under phytoplasma stress. These results suggest that ZjWRKYs play significant roles in phytoplasma tolerance and should be crucial candidate genes for jujube-phytoplasma interaction. Conclusions 54 ZjWRKYs in Chinese jujube were identified and classified into three subgroups. 41 ZjWRKYs were unevenly distributed along the chromosomes. The majority of ZjWRKYs were highly expressed in various tissues. Most of the ZjWRKYs were positive responses to phytoplasma invasion, and that provided candidate genes for the future studies of jujube-phytoplasma interaction. Electronic supplementary material The online version of this article (10.1186/s12864-019-5789-8) contains supplementary material, which is available to authorized users.

Identification and expression analysis of the WRKY gene family during different developmental stages in Lycium ruthenicum Murr. fruit

“…Some members of group 2c ( AtWRKY10, -28, -57, -75, and OsWRKY72 ) in A. thaliana and O. sativa have been reported to be involved in salt stress, flowering, seed development, and coloration ( Chen et al., 2018a ; Chen et al., 2018b ); these members have homologous relationships with LrWRKY (-3, -6, -12, -13, -18, -20, -33, and -36) in group 2c. In addition, ZjWRKY26; VvWRKY14, -19, -52; and FvWRKY4, -46, and -48, belonging to group 2c, have been reported to be mainly involved in the developmental process of fruits in Z. jujube ( Xue et al, 2019 ), V. vinifera ( Wang et al, 2014 ), and F. vesca ( Zhou et al, 2016 ) respectively. Similarly, the group 2d subfamily genes are involved in the regulation of growth and development.…”

“…The WRKY gene family also plays a crucial role in the developmental and ripening processes of fruits; for example, FvWRKY4, -46 , and -48 in group 2c are involved in fruit development and ripening in F. vesca ( Zhou et al, 2016 ). In Ziziphus jujube ZjWRKY8, -26, -47, and -48 are involved in developmental process in younger fruits ( Xue et al, 2019 ). In addition to the involvement in seed or fruit development, the WRKY genes also control seed pigmentation.…”

Genome-wide identification of CNGC genes in Chinese jujube (Ziziphus jujuba Mill.) and ZjCNGC2 mediated signalling cascades in response to cold stress

“…Our results showed that ZjCNGC2 could be regulated by cAMP and oryzalin treatments, indicating that cAMP and MTs could regulate ZjCNGC2 activity for early signal transduction. Furthermore, ZjCNGC2 could interact with ZjMAPKK4, and ZjMAPKKs have been demonstrated to interact with ZjWRKYs [42]. Finally, we arrived at a supposed model of cAMP-and MTsregulated ZjCNGC2 signalling pathways involved in cold stress (Fig.…”

“…Then, the constructs were cloned into the pGADT7 and pGBKT7 vectors, respectively, and the constructive vectors were co-transformed into the AH109 strain. Finally, the yeast clones were selected on synthetically defined medium lacking tryptophan and leucine (−LW) and medium lacking leucine, tryptophan, histidine (−LWH), −LWH medium supplemented with 7 mM 3-amino-1,2,4-triazole (3-AT; Sigma Aldrich) (−LWH + 3AT) and medium lacking leucine, tryptophan, histidine, adenine (−LWAH) as described by Xue et al (2019) [42].…”

The historical and current research progress on jujube–a superfruit for the future

“…Specific reference genes for RT-qPCR of jujube were selected under a variety of conditions and sourced from different tissues/organs, fruit development stages, and biotic/abiotic stresses, providing more choices for further gene expression analysis and functional studies in jujube [22][23][24][25][26] .…”