Genome-Wide Identification and Expression Analysis of GASA Genes in Hevea brasiliensis Reveals Their Involvement in Response to Cold Stress

The Gibberellic Acid Stimulated in Arabidopsis (GASA) gene family is regulated by gibberellins and plays a crucial role in regulating plant growth and development. Based on rubber tree genome data, 18 HbGASA genes, designated HbGASA1 to HbGASA18, were identified in Hevea brasiliensis. Comprehensive bioinformatics analyses were performed to characterize gene structures, chromosomal distributions, syntenic relationships, protein architectures, phylogenetic evolution, and expression profiles. The expression patterns of HbGASA genes under low-temperature stress were further validated by quantitative real-time polymerase chain reactions (qRT-PCR). The results demonstrated that the 18 HbGASA genes were unevenly distributed across 10 chromosomes. The encoded proteins ranged from 88 to 253 amino acids in length, and the number of exons varied from 2 to 4. Phylogenetic analysis clustered these genes into three distinct clades. Conserved motif analysis identified 10 conserved motifs, with Motif 1 and Motif 2 being highly conserved across all members. Promoter analysis revealed multiple hormone-responsive and stress-related regulatory cis-acting elements. Transcripts of the 18 HbGASA genes were detected in various tissues, and significant differences were observed in their expression levels. Under cold stress, qRT-PCR results showed that multiple HbGASA genes were significantly up-regulated. This study provides valuable insights into the structure, evolution, and functional diversification of GASA genes in the important tropical crop, H. brasiliensis.