The Trihelix Genes in Gardenia jasminoides Evolution, Expression Profiles, and Potential Regulatory Functions in Growth, Development, and Multiple Stress Responses

Trihelix is a class of transcription factors unique to plants that play a major role in abiotic and biotic stress responses, seed isolate development, floral organ morphogenesis, and plant photomorphogenesis. Nevertheless, the Trihelix transcription factor family in Gardenia jasminoides (G. jasminoides) has not been systematically characterized. In this study, 11 GjTrihelix genes were identified from the G. jasminoides genome, unevenly distributed across five chromosomes, and can be classified into four subfamilies: GT-1, GT-2, SIP and SH4. Gene structure and functional motif analyses revealed high conservation within the same subfamily. Cis-acting element analysis showed that these genes are closely related to hormone responses, stress responses, and growth and development processes. Intraspecific synteny analysis showed a segmental duplication between GjTrihelix-3 and GjTrihelix-10. Interspecific collinearity analysis revealed that G. jasminoides shared 21 collinear gene pairs with soybean, compared with five pairs with Arabidopsis and 13 with Populus, indicating greater syntenic block conservation between G. jasminoides and soybean. Transcriptome data analysis demonstrated distinct spatiotemporal expression specificity of this gene family. Several genes were constitutively expressed in fruits; GjTrihelix-1 and GjTrihelix-3 were predominantly expressed in green fruits, while GjTrihelix-11 was highly expressed in red fruits. Under melatonin treatment, five GjTrihelix genes showed significant up-regulation and obvious transcriptional suppression of another five genes. Following infection by Botryosphaeria dothidea, GjTrihelix-5 and GjTrihelix-7 were progressively induced and peaked at 72 h. qRT-PCR results indicated that most GjTrihelix genes were highly expressed in leaves, while GjTrihelix-11 was highly expressed in flowers. Most GjTrihelix genes were significantly down-regulated under NaCl, ABA, GA3 and IAA stresses. This study provides new insights into the potential association of the Trihelix transcription factor family in G. jasminoides growth, development, and stress adaptation, offering theoretical references for stress-resistant G. jasminoides breeding.