<scp> <i>ClAPRT3</i> </scp> ‐Mediated Adenine Salvage Pathway Enhances Purine Metabolites to Sustain Seed Vigour During Selfing in <scp> <i>Cunninghamia lanceolata</i> </scp>

Selfing often causes inbreeding depression, especially during seed and seedling stages. However, some selfed progeny show low inbreeding depression with enhanced vigour, differing from inbred counterparts. This study investigates the molecular mechanisms maintaining seed vigour during selfing in Cunninghamia lanceolata. Evaluation showed that selfed seeds had medium vigour compared to other inbred and non-inbred seeds. Transcriptome analysis revealed similar gene expression patterns in the radicles and hypocotyls of inbred seeds. GO enrichment analysis identified adenine salvage as a key pathway related to seed vigour in selfed seeds. Purine metabolites (AMP, ADP, ATP) were higher in inbred seeds with better vigour, correlating with increased APRT enzyme activity. APRT inhibition by 6-diaminopurine had varying effects: high-vigour seeds were significantly inhibited, low-vigour seeds showed weaker inhibition, and selfed seeds exhibited an intermediate response. The addition of adenine and AMP partially restored seed vigour, further supporting the role of adenine salvage in vigour maintenance. A significant positive correlation (r > 0.922, p < 0.0001) between ClAPRT3 expression and APRT activity suggests that ClAPRT3 reflects APRT activity. Consistently, ClAPRT3 overexpression in Arabidopsis thaliana significantly enhanced radicle and hypocotyl length. Although ClMYB23 negatively regulates ClAPRT3 expression, no mutation was detected in the MYB binding motif among inbred progeny. Instead, variations in the ClAPRT3 coding sequence led to differences in binding energy with its ligand, which may partially explain the observed differences in APRT activity. These findings provide insights into the transcriptional and metabolic regulation of adenine salvage in maintaining seed vigour under inbreeding.