Unveiling the evolution of VIP1 subgroup bZIP transcription factors in plants and the positive effects of BdiVIP1A on heat stress response in Brachypodium distachyon.

Key message: Plant VIP1 subgroup bZIPs have been characterized, VIP1 orthologs were angiosperm-specific; BdiVIP1A localized in the nucleus and increased plant heat tolerance. In plants, group I basic region/leucine zipper motif (bZIP) transcription factors (TFs), particularly VIP1 and its close homologs (the VIP1 subgroup), play crucial roles in vascular development and osmosensory responses. However, the ancestral origins and evolutionary processes underlying their functional diversity across plant lineages remain poorly understood. In this study, we delve into the origin of VIP1 subgroup bZIP homologs to an ancestral lineage present in charophytes, predating the emergence of land plants. Our phylogenetic analysis identified five distinct clades (A to E), highlighting an early diversification of these genes. Notably, our findings emphasize that VIP1 orthologs represent an angiosperm-specific innovation characterized by dynamic motif gain and/or loss events, as well as relaxed purifying selection, reflecting a unique evolutionary trajectory. Synteny analysis highlights the importance of whole-genome duplication (WGD) events preceding angiosperm divergence in the formation of the bZIP18/bZIP52 group. Codon usage analysis further revealed distinct patterns: monocots exhibited a preference for G3s, C3s, GC3, and overall GC content, whereas dicots showed a tendency toward T3s and A3s. Weighted gene co-expression network analysis (WGCNA) identified a turquoise module significantly associated with the heat stress response, in which BdiVIP1A was identified as a hub gene involved in the response to heat stress in Brachypodium distachyon. Functionally, BdiVIP1A was a nuclear-localized protein that responds to heat stress. Overexpression of BdiVIP1A enhanced thermotolerance by increasing the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), thereby effectively scavenging reactive oxygen species (ROS). Overall, this research not only elucidates the functional significance of BdiVIP1A in plant responses to heat stress but also deepens our understanding of the evolutionary history of the VIP1 subgroup bZIP homologs. These findings contribute valuable knowledge to ongoing discussions on plant adaptation and survival strategies in the context of global climate change.