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 <i>Arabidopsis (GASA</i>) gene family is regulated by gibberellins and plays a crucial role in regulating plant growth and development. Based on rubber tree genome data, 18 <i>HbGASA</i> genes, designated <i>HbGASA1</i> to <i>HbGASA18</i>, were identified in <i>Hevea brasiliensis</i>. Comprehensive bioinformatics analyses were performed to characterize gene structures, chromosomal distributions, syntenic relationships, protein architectures, phylogenetic evolution, and expression profiles. The expression patterns of <i>HbGASA</i> genes under low-temperature stress were further validated by quantitative real-time polymerase chain reactions (qRT-PCR). The results demonstrated that the 18 <i>HbGASA</i> 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 <i>cis</i>-acting elements. Transcripts of the 18 <i>HbGASA</i> genes were detected in various tissues, and significant differences were observed in their expression levels. Under cold stress, qRT-PCR results showed that multiple <i>HbGASA</i> genes were significantly up-regulated. This study provides valuable insights into the structure, evolution, and functional diversification of <i>GASA</i> genes in the important tropical crop, <i>H. brasiliensis.</i>