Genome-wide identification and expression analysis of C2H2 zinc finger proteins in Chinese jujube (Ziziphus jujuba Mill.) in different fruit development stages and under different levels of water stress

Abstract

The C2H2 type zinc finger proteins (C2H2-ZFPs) are prevalent motifs found widely across the eukaryotic kingdom, playing crucial roles in various biological processes, including stress responses and plant growth and development. To date, C2H2-ZFPs have been identified in many plant systems, but there have been no reports in Chinese jujube (Ziziphus jujuba Mill.). In this study, a total of 77 ZjC2H2-ZFPs were identified in Chinese jujube and classified into three groups, with set A containing 29 genes, set B containing two genes, and set C containing 46 genes. The set A group genes were further divided into three groups: A1, A2, and A4 (with no member of the A3 subgroup found in jujube). The set C C2H2-ZFPs genes were also further divided into three groups: C1 containing 24 genes, C2 with two genes, and C3 with three genes. These ZjC2H2-ZFPs were distributed on 12 chromosomes and one tandem duplicated pair of ZjC2H2-ZFPs was found on chromosome 4 (ZjC2H2-21 with ZjC2H2-22). Notably, the 77 ZjC2H2-ZFPs identified in this study lacked finger clusters comprising 10 or more repeats. The structure and protein motif analysis of ZjC2H2-ZFPs showed that most C1 subgroup members were enriched with ‘QALGGH’ motif zinc finger helices and the A1a ZjC2H2-ZFPs contained highly conserved ‘SATALLQKAAQMGS’ residues in jujube. A unique finding was the discovery of a conserved non-finger domain (PCYCC motif) in A1 group members, absent in other ZjC2H2-ZFPs and unreported in other species. The enzyme activity of jujube leaves under different water stress treatments were measured, and the results showed that as the degree of water stress increased, the activity of SOD enzymes and H2O2 content also increased. The POD enzyme activity levels of different treatment groups were CK>MS>SS>LS. The levels of malondialdehyde (MDA) content observed under various treatments were notably higher and the proline content was lower in comparison to the control group (CK). Differential expression of ZjC2H2-ZFPs and specific responses were analyzed under water stress and different fruit development stages of jujube using RNA-Seq data. The correlation between expression patterns and protective enzyme activities under water stress was also examined. The results indicated that the expression levels of different ZjC2H2-ZFPs varied. A further protein interaction analysis indicated that ZjC2H2-ZFPs serve as pivotal transcriptional regulators with diverse functions, encompassing DNA or RNA binding and participation in protein interactions, with ZjC2H2-20, ZjC2H2-36, and ZjC2H2-57 being potential key players in these regulatory processes. Their roles appear particularly crucial in responding to abiotic stresses like water stress and regulating plant hormones. This study provides valuable insights into understanding stress responses and enhancing the quality of Chinese jujube during breeding.

Keywords

• C2H2 zinc finger proteins
• Chinese jujube
• Fruit development
• Phylogenetic analysis