Comprehensive analysis of the bZIP gene family in ‘Duli’ pear (Pyrus betulifolia Bunge): Insights for research on abiotic stress, especially drought, in pear

Abstract

Plants are unavoidably subjected to various abiotic stresses, such as drought, salt, and cold, during their growth and development. Drought, accompanied by water shortages in North China, has become an environmental factor seriously affecting agriculture production. Basic leucine zipper (bZIP) is one of the most diverse transcription factor families in plants. It participates in the regulation of many physiological processes and plays an important role in plants’ response to abiotic stress. In this study, for the first time, 88 bZIP family members (PbbZIPs) in ‘Duli’ pear (Pyrus betulifolia Bunge) were identified using both hidden Markov model (HMM) and basic local alignment search tool (BLAST) methods. A phylogenetic tree of all the PbbZIPs members was constructed. The physicochemical properties, subcellular localisation, chromosomal location, gene structure, conserved motifs and domains, secondary and tertiary structures, and cis-acting promoter elements of the 88 family members were comprehensively analysed. The results indicated that PbbZIPs may play relevant roles in stress response in ‘Duli’. Therefore, we determined the expressions of all PbbZIPs in ‘Duli’ seedlings under drought, salt, and cold conditions, and in seedlings treated with stress-related hormones such as abscisic acid (ABA), salicylic acid (SA), methyl jasmonate (MeJA), and melatonin (MT). PbbZIPs responsive to various abiotic stresses and hormones were screened. In addition, we determined the expression patterns of 12 PbbZIP genes that strongly responded to both drought and ABA in ‘Duli’ tissue culture plants treated with different concentrations of PEG4000 at different time points. Finally, we selected three key genes (PbbZIP65, PbbZIP77 and PbbZIP81) that may play a major role in drought resistance in ‘Duli’, and preliminarily identified their function through the VIGS method, finding that PbbZIP77 could positively regulate the drought resistance of ‘Duli’ seedlings, while PbbZIP65/81 could negatively regulate the drought resistance of ‘Duli’ seedlings. This study not only broadens our knowledge about the bZIP gene family in ‘Duli’ pear, but also provides notable guidance for further functional research on PbbZIPs in abiotic stress, especially drought resistance, in the pear plant.