Genome-wide identification and expression profiling of the SWEET gene family reveals its roles in somatic embryogenesis and stress responses in Cunninghamia lanceolata

Cunninghamia lanceolata is a major fast-growing timber species in China, yet the SWEET sugar transporter family remains largely unexplored in gymnosperms. We performed a genome-wide survey and identified 31 ClSWEET genes grouped into four clades. Conserved domain and motif analyses revealed strong intra-clade conservation: all genes carried at least one MtN3_slv domain, most contained two, and one uniquely possessed a third. Promoter profiling showed enrichment of cis-acting elements responsive to abscisic acid (ABA), methyl jasmonate (MeJA), jasmonic acid (JA), drought, and low temperature, implicating hormonal and stress regulation. Transcriptome analyses linked these features to function. During somatic embryogenesis, CULA01G01040.1 peaked at the mid-stage (day 15), whereas CULA02G72230.1 remained constitutively high. Under heat stress, eight ClSWEET genes were differentially expressed, and these expression patterns were validated by qRT-PCR. Under additional stress conditions, CULA01G01040.1 was strongly upregulated in stems in response to drought, cold stress, and anthracnose infection, whereas CULA04G40820.1 and CULA07G53650.1 were specifically induced in roots under cold stress. This study provides the first comprehensive catalog of SWEET genes in Cunninghamia lanceolata and shows that expansion of this gene family was predominantly associated with segmental duplication. Candidate genes such as CULA01G01040.1 exhibited dynamic, context-dependent expression across developmental stages and multiple stress conditions, suggesting potential roles in developmental regulation and stress responses. These findings provide a valuable resource for future functional studies and identify candidate genes for investigating the molecular basis of stress responses in Cunninghamia lanceolata .