Deciphering the genetic basis of flower opening in Lagerstroemia indica: transcriptomic and functional insights into expansin-mediated petal expansion

Lagerstroemia indica is popular for its bright flower colors and long bloom period. However, although L. indica has a long flowering period, the flowering time of a single flower is short, lasting only 1−2 d. Petal expansion is a key process that affects the length and ornamental quality of the flowering period. However, the molecular mechanism of petal expansion in L. indica remains unclear. The molecular mechanisms underlying flower opening in L. indica were investigated through transcriptome sequencing of flower buds and blooms at four developmental stages. Analysis of differentially expressed genes (DEGs) indicated enrichment in cellular processes, metabolic regulation, and biological signaling pathways. KEGG pathway analysis revealed significant roles for carbohydrate, lipid, and amino acid metabolism in the flowering process. Additional pathway analysis identified key genes and processes related to carbohydrate utilization, hormone signaling, water transport, and cell wall expansion that contribute to petal opening regulation. A comprehensive examination of the expansin gene family proteins, known for promoting cell wall loosening and extension, identified 27 expansin genes in L. indica, which were categorized into four subfamilies with conserved structures and motifs. Of these, LiEXPA10, LiEXPA19, LiEXLA1, and LiEXLA2 showed heightened expression in the later stages of flowering (S3−S4), suggesting a central role in petal expansion. Functional validation in Arabidopsis thaliana demonstrated that LiEXLA1 and LiEXLA2 promote accelerated flowering and enhanced petal expansion in transgenic lines. These findings offer new insights into the genetic and molecular basis of flower opening in L. indica and provide a foundation for breeding strategies aimed at improving ornamental traits.