Decoding the GRAS code: evolutionary phylogeny and functional diversification of a key gene family in Populus simonii

GRAS proteins constitute a plant-specific family of transcription factors involved in growth, development, and stress responses. Although the GRAS gene family has been extensively studied in various plant species, the comprehensive examination of the GRAS gene family in Populus simonii remains poorly characterized. In particular, its classification, evolutionary relationships, and potential functions in Populus simonii remain largely unexplored.

In this study, a total of 89 GRAS gene family members were identified in the Populus simonii genome. These genes were found to be unevenly distributed across 19 chromosomes, with chromosomes 1 and 7 harboring the highest number of GRAS genes. Based on the classification framework established for Arabidopsis thaliana, the Populus simonii GRAS genes were categorized into ten distinct subgroups. Sequence conservation analysis revealed that all PSGRAS proteins possess the conserved GRAS domain, and share several highly conserved motifs. Analysis of cis-acting elements in the promoter regions indicated the presence of multiple regulatory elements associated with light responsiveness, phytohormone signaling, stress tolerance, and developmental regulation. Expression profiling showed that PSGRAS genes exhibit tissue-specific and stress-responsive expression patterns, suggesting their functional diversification in growth, development, and abiotic stress adaptation in Populus simonii. Notably, PSGRAS20 was identified as a central hub in the predicted protein-protein interaction network, implying a potential regulatory role in coordinating the expression of other GRAS family members.

This study systematically identified and characterized 89 GRAS genes in Populus simonii, revealing their uneven chromosomal distribution, conserved structural features, and diverse expression patterns across tissues and stress conditions. The presence of cis-acting elements related to hormone signaling, stress response, and development suggests their broad regulatory roles. Notably, PSGRAS20 was identified as a potential central regulator within the gene interaction network. These findings enhance our understanding of the GRAS gene family's biological functions in Populus simonii and provide a foundation for future functional genomics and breeding applications.