Comprehensive analysis of basic leucine zipper (bZIP) genes in Avicennia marina: genomic insights and expression profiling reveal their roles in abiotic stress response mechanisms

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The basic leucine zipper ( bZIP ) transcription factor family plays a critical role in plant growth, development, and stress responses. However, a comprehensive analysis of bZIP genes in Avicennia marina , a key species for coastal ecosystem resilience, remains unexplored. In this study, we identified 105 AmbZIP genes across 26 chromosomes encoding predominantly hydrophilic proteins. Phylogenetic analysis classified them into nine clades, with enrichment in stress related groups A (23 genes) and D (19 genes). Three conserved motifs (1, 2 and 13) define the bZIP signature. Promoter analysis revealed 2,133 cis-elements, primarily involved in hormone (37%), light (33%) and stress (25%) signaling. Seventy-six segmentally duplicated gene pairs evolved under strong purifying selection (Ka/Ks < 1). We identified 648 miRNAs targeting 97 AmbZIP genes, with ath-miR166 as the most abundant. Quantitative real time PCR validated six genes AmbZIP4 , AmbZIP36 , AmbZIP78 , AmbZIP84 , AmbZIP90, and, AmbZIP94 as consistently upregulated across root, shoot, and leaf tissues under cold, heat, salt, drought and abscisic acid treatments. The first genome wide-characterization of bZIP genes in A. marina establishes a foundation for understanding stress tolerance mechanisms in mangroves. The six validated candidate genes represent priority targets for functional studies aimed at enhancing coastal ecosystem resilience under climate change.

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