Genome-Wide Identification and Expression Analysis of the SPL Gene Family in Three Orchids

SPL transcription factors regulate important processes such as plant growth and development, metabolic regulation, and abiotic stress. They play crucial roles in the development of flower organs. However, little is known about the characteristics and functions of the SPLs in the Orchidaceae. In this study, Cymbidium goeringii Rchb. f., Dendrobium chrysotoxum Lindl., and Gastrodia elata BI. were used as research objects. The SPL gene family of these orchids was analyzed on a genome-wide scale, and their physicochemical properties, phylogenetic relationships, gene structures, and expression patterns were studied. Transcriptome and qRT-PCR methods were combined to investigate the regulatory effect of SPLs on the development of flower organs during the flowering process (bud, initial bloom, and full bloom). This study identifies a total of 43 SPLs from C. goeringii (16), D. chrysotoxum (17), and G. elata (10) and divides them into eight subfamilies according to the phylogenetic tree. Most SPL proteins contained conserved SBP domains and complex gene structures; half of the genes had introns longer than 10 kb. The largest number and variety of cis-acting elements associated with light reactions were enriched, accounting for about 45% of the total (444/985); 13/43 SPLs contain response elements of miRNA156. GO enrichment analysis showed that the functions of most SPLs were mainly enriched in the development of plant flower organs and stems. In addition, expression patterns and qRT-PCR analysis suggested the involvement of SPL genes in the regulation of flower organ development in orchids. There was little change in the expression of the CgoSPL in C. goeringii, but DchSPL9 and GelSPL2 showed significant expression during the flowering process of D. chrysotoxum and G. elata, respectively. In summary, this paper provides a reference for exploring the regulation of the SPL gene family in orchids.