Cytobiological and molecular mechanisms underlying hybridization fertility differences among albino tea cultivars (Camellia sinensis)

Camellia sinensis is a perennial economic crop, and albino cultivars ('Baiye No.1' (BY), 'Huangjinya' (HA), 'Huangjinye' (HE)) are valuable for hybrid breeding but exhibit distinct hybridization seed set rates. This study explored these differences via three consecutive years of artificial cross-pollination (male parent: 'Longjing 43' (LJ)), combined with cytological observations, multi-omics analysis, molecular interaction assays and heterologous validation. Results showed HE had a significantly higher three-year average seed set rate (74.33%) than HA (21.00%) and BY (24.00%). Cytologically, HA and BY displayed abnormal pollen tube growth (delayed elongation, stalling near micropyle) and defective ovule development at 72 HAP, while HE developed normally. Multi-omics analysis linked HE's high fertility to coordinated carbohydrate metabolism, amino acid biosynthesis and reproductive-related transcriptional programs in pistils-responses absent in HA and BY. Molecular studies identified CsIMB3b interacted with CsRPL27a, and its heterologous expression partially rescued embryonic development defects in Arabidopsis thaliana imb3 mutants. In conclusion, hybrid seed set variation among these albino tea cultivars correlates with pollen tube/ovule development abnormalities and metabolic/transcriptional dysregulation. CsIMB3b serves as a candidate gene associated with fertility. These findings provide a cytological and molecular basis for understanding fertility differences and guiding targeted tea hybrid breeding, with practical applications pending further tea-specific validation.