GhNTF2.1 facilitates cotton fiber elongation by regulating sucrose metabolism through interacting with GhABI5

Cotton fiber length is a critical determinant of textile quality, influencing yarn strength and spinning efficiency. Understanding the molecular mechanisms underlying fiber elongation is therefore essential for genetic improvement. In this study, the principal component analysis (PCA) of transcriptome data (0-25 days post-anthesis) from four Gossypium hirsutum cultivars, including two long-staple and two short-staple varieties, showed that PC1 (49.86 %) and PC2 (28.82 %) together explained 78.68 % of the total variance, clearly separating samples by developmental stage and fiber length genotype. Based on the weighted gene co-expression network analysis, brown module which was strongly correlated with the rapid elongation stage (5-10 days post-anthesis), was also significantly associated with fiber length. Gene significance and module membership analyses pinpointed GhNTF2.1, belonging to nuclear transport factor 2 gene family in cotton, as a central hub gene. Overexpressing GhNTF2.1 in cotton significantly increased fiber length compared to WT (WT: 28.01 ± 1.06 mm; OE: 30.18 ± 0.85 mm; p < 0.01). However, silencing GhNTF2.1 significantly reduced cotton fiber length via virus-induced gene silencing technology. Mechanistically, GhNTF2.1 interacted with GhABI5 to facilitate the nuclear import of GhABI5, thereby promoting transcription of GhCWINV, a key enzyme in sucrose metabolism. Targeted metabolomic profiling revealed that overexpression of GhNTF2.1 promoted the accumulation of sucrose-derived metabolites, amino acids, and other secondary metabolites. Our study uncovers a previously uncharacterized regulatory module, GhNTF2.1-GhABI5-GhCWINV, which facilitates cotton fiber elongation and provides valuable genetic targets for fiber quality improvement.